Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands
Identifieur interne : 001377 ( Istex/Corpus ); précédent : 001376; suivant : 001378Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands
Auteurs : Stephen M. Pugh ; Alexander J. Blake ; Lutz H. Gade ; Philip MountfordSource :
- Inorganic Chemistry [ 0020-1669 ] ; 2001.
Abstract
Reaction of the vanadium(V) imide [V(NAr)Cl3(THF)] (Ar = 2,6-C6H3iPr2) with the diamino-pyridine derivative MeC(2-C5H4N)(CH2NHSiMe2tBu)2 (abbreviated as H2N‘2Npy) gave modest yields of the vanadium(IV) species [V(NAr)(H3N‘N‘ ‘Npy)Cl2] (1 where H3N‘N‘ ‘Npy = MeC(2- C5H4N)(CH2NH2)(CH2NHSiMe2tBu) in which the original H2N‘2Npy has effectively lost SiMe2tBu (as ClSiMe2tBu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl3(py)2] (M = Nb or Ta, R = tBu or Ar) and the dilithium salt Li2[N2Npy] (where H2N2Npy = MeC(2-C5H4N)(CH2NHSiMe3)2), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = tBu 2; M = Ta, R = tBu 3 or Ar 4). The compounds 2−4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2Npy)]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(NtBu)Cl(N2Npy)] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported.
New Group 5 imido complexes derived from the diamido-pyridine ligand MeC(2-C5H4N)(CH2CH2NSiMe3)2 (N2Npy) are described. Among those reported are products of the reactions of Li2[N2Npy] with [M(NR)Cl3(py)2] (M = Nb, Ta; R = tBu, Ar) which gave compounds of the type shown. The X-ray structures and solution dynamics of the new compounds are described.
Url:
DOI: 10.1021/ic0102541
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Blake</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> University of Nottingham.</mods:affiliation></affiliation></author><author><name sortKey="Gade, Lutz H" sort="Gade, Lutz H" uniqKey="Gade L" first="Lutz H." last="Gade">Lutz H. Gade</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> Université Louis Pasteur.</mods:affiliation></affiliation><affiliation><mods:affiliation> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</mods:affiliation></affiliation></author><author><name sortKey="Mountford, Philip" sort="Mountford, Philip" uniqKey="Mountford P" first="Philip" last="Mountford">Philip Mountford</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> University of Oxford.</mods:affiliation></affiliation><affiliation><mods:affiliation> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. 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Pugh</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> University of Oxford.</mods:affiliation></affiliation></author><author><name sortKey="Blake, Alexander J" sort="Blake, Alexander J" uniqKey="Blake A" first="Alexander J." last="Blake">Alexander J. Blake</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> University of Nottingham.</mods:affiliation></affiliation></author><author><name sortKey="Gade, Lutz H" sort="Gade, Lutz H" uniqKey="Gade L" first="Lutz H." last="Gade">Lutz H. Gade</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> Université Louis Pasteur.</mods:affiliation></affiliation><affiliation><mods:affiliation> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</mods:affiliation></affiliation></author><author><name sortKey="Mountford, Philip" sort="Mountford, Philip" uniqKey="Mountford P" first="Philip" last="Mountford">Philip Mountford</name><affiliation><mods:affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</mods:affiliation></affiliation><affiliation><mods:affiliation> University of Oxford.</mods:affiliation></affiliation><affiliation><mods:affiliation> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j" type="main">Inorganic Chemistry</title><title level="j" type="abbrev">Inorg. Chem.</title><idno type="ISSN">0020-1669</idno><idno type="eISSN">1520-510X</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2001-06-30">2001</date><date when="2001-07-30">2001</date><biblScope unit="vol">40</biblScope><biblScope unit="issue">16</biblScope><biblScope unit="page" from="3992">3992</biblScope><biblScope unit="page" to="4001">4001</biblScope></imprint><idno type="ISSN">0020-1669</idno></series></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0020-1669</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract">Reaction of the vanadium(V) imide [V(NAr)Cl3(THF)] (Ar = 2,6-C6H3iPr2) with the diamino-pyridine derivative MeC(2-C5H4N)(CH2NHSiMe2tBu)2 (abbreviated as H2N‘2Npy) gave modest yields of the vanadium(IV) species [V(NAr)(H3N‘N‘ ‘Npy)Cl2] (1 where H3N‘N‘ ‘Npy = MeC(2- C5H4N)(CH2NH2)(CH2NHSiMe2tBu) in which the original H2N‘2Npy has effectively lost SiMe2tBu (as ClSiMe2tBu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl3(py)2] (M = Nb or Ta, R = tBu or Ar) and the dilithium salt Li2[N2Npy] (where H2N2Npy = MeC(2-C5H4N)(CH2NHSiMe3)2), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = tBu 2; M = Ta, R = tBu 3 or Ar 4). The compounds 2−4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2Npy)]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(NtBu)Cl(N2Npy)] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported.</div><div type="abstract">New Group 5 imido complexes derived from the diamido-pyridine ligand MeC(2-C5H4N)(CH2CH2NSiMe3)2 (N2Npy) are described. Among those reported are products of the reactions of Li2[N2Npy] with [M(NR)Cl3(py)2] (M = Nb, Ta; R = tBu, Ar) which gave compounds of the type shown. 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Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</json:string><json:string>University of Oxford.</json:string></affiliations></json:item><json:item><name>BLAKE Alexander J.</name><affiliations><json:string>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</json:string><json:string>University of Nottingham.</json:string></affiliations></json:item><json:item><name>GADE Lutz H.</name><affiliations><json:string>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</json:string><json:string>Université Louis Pasteur.</json:string><json:string>To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</json:string></affiliations></json:item><json:item><name>MOUNTFORD Philip</name><affiliations><json:string>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</json:string><json:string>University of Oxford.</json:string><json:string>To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</json:string></affiliations></json:item></author><arkIstex>ark:/67375/TPS-BHD9X61C-B</arkIstex><language><json:string>unknown</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>Reaction of the vanadium(V) imide [V(NAr)Cl3(THF)] (Ar = 2,6-C6H3iPr2) with the diamino-pyridine derivative MeC(2-C5H4N)(CH2NHSiMe2tBu)2 (abbreviated as H2N‘2Npy) gave modest yields of the vanadium(IV) species [V(NAr)(H3N‘N‘ ‘Npy)Cl2] (1 where H3N‘N‘ ‘Npy = MeC(2- C5H4N)(CH2NH2)(CH2NHSiMe2tBu) in which the original H2N‘2Npy has effectively lost SiMe2tBu (as ClSiMe2tBu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl3(py)2] (M = Nb or Ta, R = tBu or Ar) and the dilithium salt Li2[N2Npy] (where H2N2Npy = MeC(2-C5H4N)(CH2NHSiMe3)2), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = tBu 2; M = Ta, R = tBu 3 or Ar 4). The compounds 2−4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2Npy)]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(NtBu)Cl(N2Npy)] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported.</abstract><qualityIndicators><score>8.944</score><pdfWordCount>7405</pdfWordCount><pdfCharCount>42191</pdfCharCount><pdfVersion>1.2</pdfVersion><pdfPageCount>10</pdfPageCount><pdfPageSize>612 x 792 pts (letter)</pdfPageSize><pdfWordsPerPage>741</pdfWordsPerPage><pdfText>true</pdfText><refBibsNative>true</refBibsNative><abstractWordCount>162</abstractWordCount><abstractCharCount>1113</abstractCharCount><keywordCount>0</keywordCount></qualityIndicators><title>Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands</title><genre><json:string>research-article</json:string></genre><host><title>Inorganic Chemistry</title><language><json:string>unknown</json:string></language><issn><json:string>0020-1669</json:string></issn><eissn><json:string>1520-510X</json:string></eissn><volume>40</volume><issue>16</issue><pages><first>3992</first><last>4001</last></pages><genre><json:string>journal</json:string></genre></host><ark><json:string>ark:/67375/TPS-BHD9X61C-B</json:string></ark><categories><wos><json:string>1 - science</json:string><json:string>2 - chemistry, inorganic & nuclear</json:string></wos><scienceMetrix><json:string>1 - natural sciences</json:string><json:string>2 - chemistry</json:string><json:string>3 - inorganic & nuclear chemistry</json:string></scienceMetrix><scopus><json:string>1 - Physical Sciences</json:string><json:string>2 - Chemistry</json:string><json:string>3 - Inorganic Chemistry</json:string><json:string>1 - Physical Sciences</json:string><json:string>2 - Chemistry</json:string><json:string>3 - Physical and Theoretical Chemistry</json:string></scopus><inist><json:string>1 - sciences appliquees, technologies et medecines</json:string><json:string>2 - sciences biologiques et medicales</json:string><json:string>3 - sciences biologiques fondamentales et appliquees. psychologie</json:string><json:string>4 - genetique des eucaryotes. evolution biologique et moleculaire</json:string></inist></categories><publicationDate>2001</publicationDate><copyrightDate>2001</copyrightDate><doi><json:string>10.1021/ic0102541</json:string></doi><id>D6A7FC5D2E9DFB03A59535075204206D6A350B5F</id><score>1</score><fulltext><json:item><extension>pdf</extension><original>true</original><mimetype>application/pdf</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-BHD9X61C-B/fulltext.pdf</uri></json:item><json:item><extension>zip</extension><original>false</original><mimetype>application/zip</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-BHD9X61C-B/bundle.zip</uri></json:item><json:item><extension>txt</extension><original>false</original><mimetype>text/plain</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-BHD9X61C-B/fulltext.txt</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/ark:/67375/TPS-BHD9X61C-B/fulltext.tei"><teiHeader><fileDesc><titleStmt><title level="a" type="main">Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>American Chemical Society</publisher><availability><licence>Copyright © 2001 American Chemical Society</licence><p>American Chemical Society</p></availability><date type="e-published" when="2001-06-30">2001</date><date when="2001-07-30">2001</date><date type="Copyright" when="2001">2001</date></publicationStmt><notesStmt><note type="content-type" source="research-article" scheme="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</note><note type="publication-type" scheme="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</note></notesStmt><sourceDesc><biblStruct type="article"><analytic><title level="a" type="main" xml:lang="en">Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands</title><author xml:id="author-0000"><persName><surname>Pugh</surname><forename type="first">Stephen M.</forename></persName><affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,
School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,
and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,
Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
</affiliation><note place="foot"><ref>†</ref><p>
University of Oxford.</p></note></author><author xml:id="author-0001"><persName><surname>Blake</surname><forename type="first">Alexander J.</forename></persName><affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,
School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,
and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,
Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
</affiliation><note place="foot"><ref>‡</ref><p>
University of Nottingham.</p></note></author><author xml:id="author-0002" role="corresp"><persName><surname>Gade</surname><forename type="first">Lutz H.</forename></persName><affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,
School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,
and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,
Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
</affiliation><note place="foot"><ref>§</ref><p>
Université Louis Pasteur.</p></note><affiliation role="corresp"> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@ chemistry.oxford.ac.uk. Fax: +44 1865 272690</affiliation></author><author xml:id="author-0003" role="corresp"><persName><surname>Mountford</surname><forename type="first">Philip</forename></persName><affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,
School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,
and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,
Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
</affiliation><note place="foot"><ref>†</ref><p>
University of Oxford.</p></note><affiliation role="corresp"> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@ chemistry.oxford.ac.uk. Fax: +44 1865 272690</affiliation></author><idno type="istex">D6A7FC5D2E9DFB03A59535075204206D6A350B5F</idno><idno type="ark">ark:/67375/TPS-BHD9X61C-B</idno><idno type="DOI">10.1021/ic0102541</idno></analytic><monogr><title level="j" type="main">Inorganic Chemistry</title><title level="j" type="abbrev">Inorg. Chem.</title><idno type="acspubs">ic</idno><idno type="coden">inocaj</idno><idno type="pISSN">0020-1669</idno><idno type="eISSN">1520-510X</idno><imprint><publisher>American Chemical Society</publisher><date type="e-published" when="2001-06-30">2001</date><date when="2001-07-30">2001</date><biblScope unit="vol">40</biblScope><biblScope unit="issue">16</biblScope><biblScope unit="page" from="3992">3992</biblScope><biblScope unit="page" to="4001">4001</biblScope></imprint></monogr></biblStruct></sourceDesc></fileDesc><profileDesc><abstract><graphic url="ic0102541n00001.tif"></graphic><p>Reaction of the vanadium(V) imide [V(NAr)Cl<hi rend="subscript">3</hi>(THF)] (Ar = 2,6-C<hi rend="subscript">6</hi>H<hi rend="subscript">3</hi><hi rend="italic"><hi rend="superscript">i</hi></hi>Pr<hi rend="subscript">2</hi>) with the diamino-pyridine derivative
MeC(2-C<hi rend="subscript">5</hi>H<hi rend="subscript">4</hi>N)(CH<hi rend="subscript">2</hi>NHSiMe<hi rend="subscript">2</hi><hi rend="italic"><hi rend="superscript">t</hi></hi>Bu)<hi rend="subscript">2</hi> (abbreviated as H<hi rend="subscript">2</hi>N‘<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>) gave modest yields of the vanadium(IV) species
[V(NAr)(H<hi rend="subscript">3</hi>N‘N‘ ‘N<hi rend="subscript">py</hi>)Cl<hi rend="subscript">2</hi>] (<hi rend="bold">1</hi> where H<hi rend="subscript">3</hi>N‘N‘ ‘N<hi rend="subscript">py</hi> = MeC(2- C<hi rend="subscript">5</hi>H<hi rend="subscript">4</hi>N)(CH<hi rend="subscript">2</hi>NH<hi rend="subscript">2</hi>)(CH<hi rend="subscript">2</hi>NHSiMe<hi rend="subscript">2</hi><hi rend="italic"><hi rend="superscript">t</hi></hi>Bu) in which the
original H<hi rend="subscript">2</hi>N‘<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi> has effectively lost SiMe<hi rend="subscript">2</hi><hi rend="italic"><hi rend="superscript">t</hi></hi>Bu (as ClSiMe<hi rend="subscript">2</hi><hi rend="italic"><hi rend="superscript">t</hi></hi>Bu) and gained an H atom. Better behaved reactions
were found between the heavier Group 5 metal complexes [M(NR)Cl<hi rend="subscript">3</hi>(py)<hi rend="subscript">2</hi>] (M = Nb or Ta, R = <hi rend="italic"><hi rend="superscript">t</hi></hi>Bu or Ar) and
the dilithium salt Li<hi rend="subscript">2</hi>[N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>] (where H<hi rend="subscript">2</hi>N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi> = MeC(2-C<hi rend="subscript">5</hi>H<hi rend="subscript">4</hi>N)(CH<hi rend="subscript">2</hi>NHSiMe<hi rend="subscript">3</hi>)<hi rend="subscript">2</hi>), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>)(py)] (M = Nb, R = <hi rend="italic"><hi rend="superscript">t</hi></hi>Bu <hi rend="bold">2</hi>; M = Ta, R = <hi rend="italic"><hi rend="superscript">t</hi></hi>Bu <hi rend="bold">3</hi> or Ar <hi rend="bold">4</hi>). The
compounds <hi rend="bold">2</hi>−<hi rend="bold">4</hi> are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>)]. Activation parameters are reported for the complexes <hi rend="bold">2</hi> and <hi rend="bold">3</hi>. In the
case of <hi rend="bold">2</hi>, high vacuum tube sublimation afforded modest quantities of [Nb(N<hi rend="italic"><hi rend="superscript">t</hi></hi>Bu)Cl(N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>)] (<hi rend="bold">5</hi>). The X-ray
crystal structures of the four compounds <hi rend="bold">1</hi>, <hi rend="bold">2</hi>, <hi rend="bold">3</hi>, and <hi rend="bold">4</hi> are reported.
</p></abstract><abstract><p>New Group 5 imido complexes derived from the diamido-pyridine ligand MeC(2-C<hi rend="subscript">5</hi>H<hi rend="subscript">4</hi>N)(CH<hi rend="subscript">2</hi>CH<hi rend="subscript">2</hi>NSiMe<hi rend="subscript">3</hi>)<hi rend="subscript">2</hi> (N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>) are described. Among those reported are products of the reactions of Li<hi rend="subscript">2</hi>[N<hi rend="subscript">2</hi>N<hi rend="subscript">py</hi>] with [M(NR)Cl<hi rend="subscript">3</hi>(py)<hi rend="subscript">2</hi>] (M = Nb, Ta; R = <hi rend="italic"><hi rend="superscript">t</hi></hi>Bu, Ar) which gave compounds of the type shown. The X-ray structures and solution dynamics of the new compounds are described.</p></abstract><textClass ana="subject"><keywords scheme="document-type-name"><term>Article</term></keywords></textClass><langUsage><language ident="zxx"></language></langUsage></profileDesc></teiHeader></istex:fulltextTEI></fulltext><metadata><istex:metadataXml wicri:clean="corpus acs not found" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="UTF-8"</istex:xmlDeclaration><istex:document><article article-type="research-article" specific-use="acs2jats-1.1.23" dtd-version="1.1d1"><front><journal-meta><journal-id journal-id-type="acspubs">ic</journal-id><journal-id journal-id-type="coden">inocaj</journal-id><journal-title-group><journal-title>Inorganic Chemistry</journal-title><abbrev-journal-title>Inorg. Chem.</abbrev-journal-title></journal-title-group><issn pub-type="ppub">0020-1669</issn><issn pub-type="epub">1520-510X</issn><publisher><publisher-name>American Chemical Society</publisher-name></publisher><self-uri>pubs.acs.org/IC</self-uri></journal-meta><article-meta><article-id pub-id-type="doi">10.1021/ic0102541</article-id><article-categories><subj-group subj-group-type="document-type-name"><subject>Article</subject></subj-group></article-categories><title-group><article-title>Group 5 Imido Complexes Derived from Diamido-Pyridine Ligands</article-title></title-group><contrib-group><contrib contrib-type="author"><name name-style="western"><surname>Pugh</surname><given-names>Stephen M.</given-names></name><xref rid="ic0102541AF2"><sup>†</sup></xref></contrib><contrib contrib-type="author"><name name-style="western"><surname>Blake</surname><given-names>Alexander J.</given-names></name><xref rid="ic0102541AF3"><sup>‡</sup></xref></contrib><contrib contrib-type="author" corresp="yes"><name name-style="western"><surname>Gade</surname><given-names>Lutz H.</given-names></name><xref rid="ic0102541AF1">*</xref><xref rid="ic0102541AF4"><sup>§</sup></xref></contrib><contrib contrib-type="author" corresp="yes"><name name-style="western"><surname>Mountford</surname><given-names>Philip</given-names></name><xref rid="ic0102541AF1">*</xref><xref rid="ic0102541AF2"><sup>†</sup></xref></contrib><aff>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,
School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,
and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,
Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
</aff></contrib-group><author-notes><fn id="ic0102541AF2"><label>†</label><p>
University of Oxford.</p></fn><fn id="ic0102541AF3"><label>‡</label><p>
University of Nottingham.</p></fn><corresp id="ic0102541AF1">
To whom correspondence should be addressed. Lutz H. Gade e-mail:
gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@
chemistry.oxford.ac.uk. Fax: +44 1865 272690</corresp><fn id="ic0102541AF4"><label>§</label><p>
Université Louis Pasteur.</p></fn></author-notes><pub-date pub-type="epub"><day>30</day><month>06</month><year>2001</year></pub-date><pub-date pub-type="ppub"><day>30</day><month>07</month><year>2001</year></pub-date><volume>40</volume><issue>16</issue><fpage>3992</fpage><lpage>4001</lpage><supplementary-material xlink:href="ic0102541.cif" orientation="portrait" position="float"></supplementary-material><history><date date-type="received"><day>06</day><month>03</month><year>2001</year></date><date date-type="asap"><day>30</day><month>06</month><year>2001</year></date><date date-type="issue-pub"><day>30</day><month>07</month><year>2001</year></date></history><permissions><copyright-statement>Copyright © 2001 American Chemical Society</copyright-statement><copyright-year>2001</copyright-year><copyright-holder>American Chemical Society</copyright-holder></permissions><abstract><graphic content-type="abstract-graphic" xlink:href="ic0102541n00001.tif" orientation="portrait" position="float"></graphic><p>Reaction of the vanadium(V) imide [V(NAr)Cl<sub>3</sub>(THF)] (Ar = 2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>) with the diamino-pyridine derivative
MeC(2-C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>NHSiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)<sub>2</sub> (abbreviated as H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub>) gave modest yields of the vanadium(IV) species
[V(NAr)(H<sub>3</sub>N‘N‘ ‘N<sub>py</sub>)Cl<sub>2</sub>] (<bold>1</bold> where H<sub>3</sub>N‘N‘ ‘N<sub>py</sub> = MeC(2- C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>NH<sub>2</sub>)(CH<sub>2</sub>NHSiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu) in which the
original H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub> has effectively lost SiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu (as ClSiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu) and gained an H atom. Better behaved reactions
were found between the heavier Group 5 metal complexes [M(NR)Cl<sub>3</sub>(py)<sub>2</sub>] (M = Nb or Ta, R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu or Ar) and
the dilithium salt Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>] (where H<sub>2</sub>N<sub>2</sub>N<sub>py</sub> = MeC(2-C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>NHSiMe<sub>3</sub>)<sub>2</sub>), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (M = Nb, R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu <bold>2</bold>; M = Ta, R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu <bold>3</bold> or Ar <bold>4</bold>). The
compounds <bold>2</bold>−<bold>4</bold> are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)]. Activation parameters are reported for the complexes <bold>2</bold> and <bold>3</bold>. In the
case of <bold>2</bold>, high vacuum tube sublimation afforded modest quantities of [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)] (<bold>5</bold>). The X-ray
crystal structures of the four compounds <bold>1</bold>, <bold>2</bold>, <bold>3</bold>, and <bold>4</bold> are reported.
</p></abstract><abstract abstract-type="short"><p>New Group 5 imido complexes derived from the diamido-pyridine ligand MeC(2-C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub> (N<sub>2</sub>N<sub>py</sub>) are described. Among those reported are products of the reactions of Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>] with [M(NR)Cl<sub>3</sub>(py)<sub>2</sub>] (M = Nb, Ta; R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu, Ar) which gave compounds of the type shown. The X-ray structures and solution dynamics of the new compounds are described.</p></abstract><custom-meta-group><custom-meta><meta-name>document-id-old-9</meta-name><meta-value>ic0102541</meta-value></custom-meta></custom-meta-group></article-meta></front><body><sec id="d7e427"><title>Introduction</title><p>The chemistry of transition metal imido complexes (containing the NR ligand, where R is typically a hydrocarbyl group)
has continued to attract considerable attention, particularly over
the last 15 years.<named-content content-type="bibref-group"><xref rid="ic0102541b00001" ref-type="bibr"></xref>−<xref rid="ic0102541b00002" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00003" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00004" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00005" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00006" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00007" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00008" ref-type="bibr"></xref></named-content> The syntheses, reactivity, and bonding of
such complexes in a wide variety of supporting ligand environments continues to be explored. In our groups we have recently
been interested in using the diamido-pyridine and diamido-amine
ligands MeC(2-C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>NSiMe<sub>2</sub>R)<sub>2</sub> (abbreviated as N<sub>2</sub>N<sub>py</sub>
for R = Me or N‘<sub>2</sub>N<sub>py</sub> for R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)<named-content content-type="bibref-group"><xref rid="ic0102541b00009" ref-type="bibr"></xref>,<xref rid="ic0102541b00010" ref-type="bibr"></xref> </named-content>and Me<sub>3</sub>SiN(CH<sub>2</sub>CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub> (abbreviated as N<sub>2</sub>N<sub>am</sub>)<named-content content-type="bibref-group"><xref rid="ic0102541b00011" ref-type="bibr"></xref>,<xref rid="ic0102541b00012" ref-type="bibr"></xref></named-content> as flexible and versatile
supporting environments in imido chemistry.<xref rid="ic0102541b00008" ref-type="bibr"></xref> Employing these
hemi-labile ligands we have reported on the synthesis and
structures of a family of Group 4 complexes of the types <bold>I</bold>, <bold>II</bold>,
and <bold>III</bold> as shown in Chart <xref rid="ic0102541c00001"></xref>.<named-content content-type="bibref-group"><xref rid="ic0102541b00013" ref-type="bibr"></xref>−<xref rid="ic0102541b00014" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00015" ref-type="bibr"></xref></named-content> These have reactive MNR
linkages which undergo a wide range of coupling reactions with
many unsaturated organic substrates including the following:
RNC, MeCN, <italic toggle="yes"><sup>t</sup></italic><sup></sup>BuCP, ArNCO, RC<sub>2</sub>Me, and RCHCCH<sub>2</sub>.<named-content content-type="bibref-group"><xref rid="ic0102541b00013" ref-type="bibr"></xref>,<xref rid="ic0102541b00016" ref-type="bibr"></xref>−<xref rid="ic0102541b00017" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00018" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00019" ref-type="bibr"></xref></named-content>
Many of these transformations were the first, or among the first,
of their type in transition metal imido chemistry.
<fig id="ic0102541c00001" position="float" fig-type="chart" orientation="portrait"><label>1</label><graphic xlink:href="ic0102541c00001.tif" position="float" orientation="portrait"></graphic></fig></p><p>To develop this successful area of work, we recently described
attempts to use the diamido-amine ligand N<sub>2</sub>N<sub>am</sub> in Group 5
imido chemistry,<xref rid="ic0102541b00015" ref-type="bibr"></xref> but in our efforts to prepare Group 5
analogues of the compounds <bold>III</bold> (Chart <xref rid="ic0102541c00001"></xref>), we obtained mixtures
of ill-behaved oils and ligand decomposition products (<bold>IV</bold> and
<bold>V</bold>). In a more recently initiated project we found that well-defined Group 5 imides could be obtained using a chelating
diamido-amine-pyridine ligand as shown in <bold>VI</bold>.<xref rid="ic0102541b00020" ref-type="bibr"></xref> Here we report
the synthesis of Group 5 imido complexes of the diamido-pyridine ligand N<sub>2</sub>N<sub>py</sub> and its <italic toggle="yes">tert</italic>-butyl homologue N‘<sub>2</sub>N<sub>py</sub>.
</p></sec><sec id="d7e585"><title>Experimental Section</title><p><bold>General Methods and Instrumentation.</bold> All manipulations were
carried out using standard Schlenk line or drybox techniques under an
atmosphere of argon or of dinitrogen. Solvents were predried over
activated 4A molecular sieves and were refluxed over appropriate drying
agents under a dinitrogen atmosphere and collected by distillation.
Deuterated solvents were dried over potassium (C<sub>6</sub>D<sub>6</sub>) or calcium
hydride (CD<sub>2</sub>Cl<sub>2</sub>), distilled under reduced pressure, and stored under
dinitrogen in Teflon valve ampules. NMR samples were prepared under
dinitrogen in 5 mm Wilmad 507-PP tubes fitted with J. Young Teflon
valves. <sup>1</sup>H, <sup>13</sup>C-{<sup>1</sup>H}, and <sup>13</sup>C NMR spectra were recorded on Bruker
AM 300 and DPX 300 and Varian Unity Plus 500 spectrometers. <sup>1</sup>H
and <sup>13</sup>C assignments were confirmed when necessary with the use of
DEPT-135, DEPT-90, and two-dimensional <sup>1</sup>H-<sup>1</sup>H and <sup>13</sup>C-<sup>1</sup>H NMR
experiments. All spectra were referenced internally to residual protio-solvent (<sup>1</sup>H) or solvent (<sup>13</sup>C) resonances and are reported relative to
tetramethylsilane (<italic toggle="yes">δ</italic> = 0 ppm). Chemical shifts are quoted in δ (ppm)
and coupling constants in Hertz. Infrared spectra were prepared as Nujol
mulls between CsBr or NaCl plates and were recorded on Perkin-Elmer
1600 and 1710 series, Nicolet Avatar 360, or Mattson Polaris FTIR
spectrometers. Infrared data are quoted in wavenumbers (cm<sup>-1</sup>). EPR
spectra were recorded at room temperature on a Bruker EMX 6/1 RES
EPR spectrometer. Mass spectra were recorded on an AEI MS902 mass
spectrometer. Elemental analyses were carried out by the analysis
laboratories of these departments. NMR assignments for <bold>2</bold>−<bold>5 </bold>assume
the following numbering scheme for the pyridyl group of N<sub>2</sub>N<sub>py</sub>:
<fig id="ic0102541f1" position="float" orientation="portrait"><label></label><graphic xlink:href="ic0102541f1.tif" position="float" orientation="portrait"></graphic></fig></p><p><bold>Literature Preparations. </bold>H<sub>2</sub>N<sub>2</sub>N<sub>py</sub>,<xref rid="ic0102541b00009" ref-type="bibr"></xref> H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub>,<xref rid="ic0102541b00010" ref-type="bibr"></xref> Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>],<xref rid="ic0102541b00010" ref-type="bibr"></xref> [M(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl<sub>3</sub>(py)<sub>2</sub>] (M = Nb, Ta),<xref rid="ic0102541b00021" ref-type="bibr"></xref> [Ta(NAr)Cl<sub>3</sub>(py)<sub>2</sub>],<xref rid="ic0102541b00022" ref-type="bibr"></xref> and [V(NAr)Cl<sub>3</sub>(thf)]<xref rid="ic0102541b00023" ref-type="bibr"></xref> were prepared according to literature methods.
</p><p><bold>[V(NAr)Cl</bold><bold><sub>2</sub></bold><bold>(H</bold><bold><sub>3</sub></bold><bold>N</bold>‘<bold>N</bold>‘ ‘<bold>N</bold><bold><sub>py</sub></bold><bold>)] (1). </bold>A solution of H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub> (0.296 g, 0.75
mmol) and Et<sub>3</sub>N (0.196 g, 1.94 mmol) in diethyl ether (3 mL) was
added to a solution of [V(N-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>)Cl<sub>3</sub>(thf)] (0.304 g, 0.75 mmol)
in diethyl ether (10 mL) at −45 °C. The resulting brown solution was
allowed to warm slowly to room temperature and was stirred for 5 h.
It was then filtered and the residues were washed with diethyl ether (3
× 10 mL), the washings being added to the reaction solution. After
standing at room temperature for 48 h, red-brown X-ray diffraction
quality crystals of [V(NAr)Cl<sub>2</sub>(HN‘N‘ ‘N<sub>py</sub>)] (<bold>1</bold>) formed from the
solution. These were filtered off and dried under reduced pressure.
Yield: 0.050 g (12%). EPR: <italic toggle="yes">g</italic>-factor = 1.982, hyperfine coupling =
90.9091 G (thf, 298 K). EI mass spectrum: <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic> = 177 [M<sup>+</sup> − V(N-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>)Cl<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>Me<sub>2</sub>], <italic toggle="yes">m</italic>/<italic toggle="yes">z</italic> = 162 [M<sup>+</sup> − V(N-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>)Cl<sub>2</sub>CH<sub>2</sub>NH<sub>2</sub>Me<sub>3</sub>]. IR (CsBr plates, Nujol, cm<sup>-1</sup>): 3349 (w), 3236 (m), 3158
(w), 1731 (w), 1603 (s), 1572 (w), 1323 (w), 1257 (s), 1096 (m), 1035
(s), 934 (w), 860 (m), 829 (s), 798 (w), 780 (m), 754 (s), 712 (m), 660
(w), 635 (w), 610 (w), 552 (w), 465 (w), 436 (w), 417 (w) cm<sup>-1</sup>. Anal.
Found (calculated for C<sub>27</sub>H<sub>46</sub>Cl<sub>2</sub>N<sub>4</sub>SiV): C 56.1 (56.2), H 8.4 (8.0), N
9.5 (9.7)%.
</p><p><bold>[Nb(N</bold><bold><italic toggle="yes"><sup>t</sup></italic></bold><sup></sup><bold>Bu)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)] (2). </bold>To a mixture of solid [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl<sub>3</sub>(py)<sub>2</sub>] (1.568 g, 3.66 mmol) and solid Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>] (1.176 g, 3.66 mmol)
was added cold (7 °C) benzene (30 mL). The resulting brown solution
was stirred at room temperature for 4 h before being filtered. The
insolubles were dried under reduced pressure and extracted into
dichloromethane (2 × 20 mL) to provide a red-brown solution. This
was filtered and the volatiles removed under reduced pressure leaving
a yellow-brown solid. The solid was washed with diethyl ether (3 × 5
mL) and dried under reduced pressure to provide [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>2</bold>) as a yellow powder. Yield: 1.328 g (62%). Yellow crystals
of <bold>2 </bold>suitable for X-ray diffraction were prepared by slow cooling of a
saturated solution of <bold>2 </bold>in toluene from 100 °C to room temperature
over 10 h. <sup>1</sup>H NMR (CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 298 K): 8.77 (2 H, dt, <sup>3</sup>J
(<italic toggle="yes">o</italic>-H<italic toggle="yes">m</italic>-H) = 4.8 Hz, <sup>4</sup>J (<italic toggle="yes">o</italic>-H<italic toggle="yes">p</italic>-H) = 1.8 Hz, <italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 8.18 (1 H, dd,
<sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.7 Hz, <sup>4</sup>J (H<sup>6</sup>H<sup>4</sup>) = 1.5 Hz, H<sup>6</sup>), 7.74 (2 × 1 H, 2 ×
overlapping m, H<sup>4</sup>, and <italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.47 (1 H, dt, <sup>3</sup>J (H<sup>3</sup>H<sup>4</sup>) = 8.1 Hz,
<sup>4</sup>J (H<sup>3</sup>H<sup>5</sup>) = 0.9 Hz, H<sup>3</sup>), 7.21 (2 H, apparent t, apparent <italic toggle="yes">J</italic> = 5.0 Hz,
<italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 6.92 (1 H, apparent t, apparent <italic toggle="yes">J</italic> = 6.9 Hz, H<sup>5</sup>), 3.62 (2 H,
d, <sup>2</sup><italic toggle="yes">J</italic> = 12.7 Hz, CH<sub>2</sub>), 3.45 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.7 Hz, CH<sub>2</sub>), 1.52 (3 H,
s, Me of N<sub>2</sub>N<sub>py</sub>), 1.45 (9 H, s, <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu), 0.12 (18 H, s, SiMe<sub>3</sub>. <sup>1</sup>H NMR:
(CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 218 K): 8.06 (1 H, dd, <sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.7 Hz, <sup>4</sup>J
(H<sup>6</sup>H<sup>4</sup>) = 1.5 Hz, H<sup>6</sup>), 7.73 (2 × 1 H, 2 × overlapping m, H<sup>4</sup> and
<italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.46 (1 H, d, <sup>3</sup>J (H<sup>3</sup>H<sup>4</sup>) = 8.1 Hz, H<sup>3</sup>), 7.21 (2 H, broad s,
<italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 6.91 (1 H, apparent t, apparent <italic toggle="yes">J</italic> = 6.5 Hz, H<sup>5</sup>), 3.57 (1 H,
d, <sup>2</sup><italic toggle="yes">J</italic> = 13.2 Hz, CH<sub>2</sub>), 3.54 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 13.4 Hz, CH<sub>2</sub>), 3.42 (1 H,
d, <sup>2</sup><italic toggle="yes">J</italic> = 13.2 Hz, CH<sub>2</sub>), 3.36 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 13.2 Hz, CH<sub>2</sub>), 1.48 (3 H,
s, Me of N<sub>2</sub>N<sub>py</sub>), 1.39 9 H, s, <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu), 0.21 (9 H, s, SiMe<sub>3</sub>), −0.09 (9 H,
s, SiMe<sub>3</sub>), not observed: <italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>. <sup>13</sup>C-{<sup>1</sup>H} NMR (CD<sub>2</sub>Cl<sub>2</sub>, 75.5 MHz,
218 K): 163.6 (C<sup>2</sup>), 153.3 (<italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 149.4 (C<sup>6</sup>), 139.0 (C<sup>4</sup>), 138.3
(<italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 123.3 (<italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 121.1 (C<sup>5</sup>), 119.4 (C<sup>3</sup>), 66.9 (N<italic toggle="yes">C</italic>Me<sub>3</sub>),
62.7 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 62.5 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 50.0 (<italic toggle="yes">C</italic>(CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub>), 32.0
(NC<italic toggle="yes">Me</italic><sub>3</sub>), 24.6 (Me of N<sub>2</sub>N<sub>py</sub>), 1.8 (Si<italic toggle="yes">Me</italic><sub>3</sub>), 1.6 (Si<italic toggle="yes">Me</italic><sub>3</sub>). IR (CsBr plates,
Nujol, cm<sup>-1</sup>): 1601 (s), 1571 (w), 1483 (m), 1398 (w), 1294 (w), 1243
(s), 1216 (m), 1163 (w), 1161 (w), 1137 (w), 1116 (m), 1089 (m),
1075 (w), 1061 (m), 1046 (s), 1015 (m), 1008 (w), 961 (m), 910 (s),
841 (s), 809 (s), 785 (s), 756 (s), 704 (m), 641 (w), 628 (w), 599 (m),
558 (w), 535 (w), 486 (m), 446 (w), 430 (w) cm<sup>-1</sup>. Anal. Found
(calculated for C<sub>24</sub>H<sub>43</sub>ClN<sub>5</sub>NbSi<sub>2</sub>): C 49.0 (49.2), H 7.7 (7.4), N 12.4
(12.0)%.
</p><p><bold>[Ta(N</bold><bold><italic toggle="yes"><sup>t</sup></italic></bold><sup></sup><bold>Bu)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)] (3). </bold>To a mixture of solid [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl<sub>3</sub>(py)<sub>2</sub>] (0.500 g, 0.96 mmol) and solid Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>] (0.310 g, 0.96 mmol)
was added cold (7 °C) benzene (25 mL). The resulting brown solution
was stirred at room temperature for 5 h before being filtered. The
insolubles were dried under reduced pressure and extracted into
dichloromethane (2 × 15 mL) to provide a pale yellow solution. This
was filtered and the volatiles removed under reduced pressure leaving
a pale orange solid. The solid was washed with diethyl ether (2 × 3
mL) and dried under reduced pressure to provide <bold>3</bold> as a white powder.
Yield: 0.215 g (33%). Pale yellow crystals of <bold>3 </bold>suitable for X-ray
diffraction were prepared by slow cooling of a saturated solution of <bold>3</bold>
in toluene from 120 °C to room temperature over 72 h. <sup>1</sup>H NMR (CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 298 K): 8.84 (2 H, d, <sup>3</sup>J (<italic toggle="yes">o</italic>-H<italic toggle="yes">m</italic>-H) = 5.0 Hz,
<italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 8.26 (1 H, dd, <sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.7 Hz, <sup>4</sup>J (H<sup>6</sup>H<sup>4</sup>) = 1.8 Hz, H<sup>6</sup>),
7.77 (2 × 1 H, 2 × overlapping m, H<sup>4</sup> and <italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.48 (1 H, dt, <sup>3</sup>J
(H<sup>3</sup>H<sup>4</sup>) = 7.9 Hz, <sup>4</sup>J (H<sup>3</sup>H<sup>5</sup>) = 1.1 Hz, H<sup>3</sup>), 7.24 (2 H, apparent t,
apparent <italic toggle="yes">J</italic> = 5.0 Hz, <italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 6.94 (1 H, apparent t, apparent <italic toggle="yes">J</italic> =
6.0 Hz, H<sup>5</sup>), 3.70 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.1 Hz, CH<sub>2</sub>), 3.59 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5
Hz, CH<sub>2</sub>), 1.47 (3 H, s, Me of N<sub>2</sub>N<sub>py</sub>), 1.39 (9 H, s, <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu), 0.07 (18 H,
broad s, SiMe<sub>3</sub>). <sup>1</sup>H NMR (CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 223 K): 8.17 (1 H, d,
<sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.5 Hz, H<sup>6</sup>), 7.77 (1 H, overlapping m, H<sup>4</sup>), 7.77 (1 H,
overlapping m, <italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.48 (1 H, d, <sup>3</sup>J (H<sup>3</sup>H<sup>4</sup>) = 8.1 Hz, H<sup>3</sup>), 7.25
(2 H, broad s, <italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 6.96 (1 H, apparent t, apparent <italic toggle="yes">J</italic> = 6.2 Hz,
H<sup>5</sup>), 3.67 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5 Hz, CH<sub>2</sub>), 3.64 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.3 Hz,
CH<sub>2</sub>), 3.55 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.9 Hz, CH<sub>2</sub>), 3.50 (1 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.7 Hz,
CH<sub>2</sub>), 1.44 (3 H, s, Me of N<sub>2</sub>N<sub>py</sub>), 1.34 (9 H, s, <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu), 0.21 (9 H, s,
SiMe<sub>3</sub>), −0.11 (9 H, s, SiMe<sub>3</sub>), not observed: <italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>. <sup>13</sup>C-{<sup>1</sup>H} NMR
(CD<sub>2</sub>Cl<sub>2</sub>, 75.5 MHz, 223 K): 164.2 (C<sup>2</sup>), 154.0 (<italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 149.7 (C<sup>6</sup>),
139.3 (C<sup>4</sup>), 138.6 (<italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 123.6 (<italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 121.5 (C<sup>5</sup>), 119.5 (C<sup>3</sup>),
65.0 (N<italic toggle="yes">C</italic>Me<sub>3</sub>), 61.8 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 61.7 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 49.8 (<italic toggle="yes">C</italic>(CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub>), 33.4 (NC<italic toggle="yes">Me</italic><sub>3</sub>), 24.3 (Me of N<sub>2</sub>N<sub>py</sub>), 1.9 (SiMe<sub>3</sub>), 1.8 (SiMe<sub>3</sub>).
IR: (CsBr plates, Nujol, cm<sup>-1</sup>): 1603 (s), 1571 (w), 1483 (m), 1385
(w), 1295 (w), 1253 (s), 1217 (m), 1160 (w), 1155 (w), 1134 (w), 1091
(w), 1076 (w), 1062 (w), 1047 (s), 1016 (m), 1009 (w), 962 (m), 918
(s), 848 (s), 782 (m), 757 (m), 703 (m), 642 (w), 630 (w), 599 (m),
560 (w), 532 (w), 488 (m), 445 (w), 431 (w) cm<sup>-1</sup>. Anal. Found
(calculated for C<sub>24</sub>H<sub>43</sub>ClN<sub>5</sub>Si<sub>2</sub>Ta): C 42.3 (42.8), H 7.0 (6.4), N 9.4
(10.4)%.
</p><p><bold>[Ta(NAr)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)] (4). </bold>To a mixture of solid [Ta(N-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>)Cl<sub>3</sub>(py)<sub>2</sub>] (0.414 g, 0.67 mmol) and solid Li<sub>2</sub>[N<sub>2</sub>N<sub>py</sub>] (0.220 g, 0.68
mmol) was added cold (7 °C) benzene (30 mL). The resulting yellow-brown solution was stirred at room temperature for 2 h, becoming dark
green during this time. The solution was filtered and the volatiles
removed under reduced pressure to leave a green-brown solid. The solid
was dissolved in diethyl ether (5 mL) and recrystallized at room
temperature over 4 days to provide yellow crystals of <bold>4</bold>. Yield: 0.235
g (45%). Pale yellow crystals of <bold>4 </bold>suitable for X-ray diffraction were
prepared by recrystallization from a 1:1 hexane/toluene solution at −25
°C over 2 weeks. <sup>1</sup>H NMR (CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 298 K): 8.84 (2 H,
dt, <sup>3</sup>J (<italic toggle="yes">o</italic>-H<italic toggle="yes">m</italic>-H) = 5.0 Hz, <sup>4</sup>J (<italic toggle="yes">o</italic>-H<italic toggle="yes">p</italic>-H) = 1.5 Hz, <italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 8.51 (1
H, d, <sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.7 Hz, H<sup>6</sup>), 7.85 (2 × 1 H, 2 × overlapping m, H<sup>4</sup>
and <italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.58 (1 H, d, <sup>3</sup>J (H<sup>3</sup>H<sup>4</sup>) = 8.1 Hz, H<sup>3</sup>), 7.32 (H, apparent
t, apparent <italic toggle="yes">J</italic> = 5.0 Hz, <italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 7.08 (H, apparent t, apparent <italic toggle="yes">J</italic> =
6.0 Hz, H<sup>5</sup>), 7.06 (2 H, d, <sup>3</sup><italic toggle="yes">J</italic> = 7.5 Hz, <italic toggle="yes">m</italic>-C<sub>6</sub><italic toggle="yes">H</italic><sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 6.69 (1 H, t, <sup>3</sup><italic toggle="yes">J</italic> =
7.5 Hz, <italic toggle="yes">p</italic>-C<sub>6</sub><italic toggle="yes">H</italic><sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 4.50 (H, broad s, C<italic toggle="yes">H</italic>Me<sub>2</sub>), 3.84 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5
Hz, CH<sub>2</sub>), 3.71 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5 Hz, CH<sub>2</sub>), 1.58 (H, s, Me of N<sub>2</sub>N<sub>py</sub>),
1.28 (12 H, d, <sup>3</sup><italic toggle="yes">J</italic> = 6.8 Hz, CH<italic toggle="yes">Me</italic><sub>2</sub>), −0.10 (18 H, s, SiMe<sub>3</sub>). <sup>1</sup>H NMR
(CD<sub>2</sub>Cl<sub>2</sub>, 300.1 MHz, 223 K): 8.69 (2 H, broad s, <italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 8.42 (1
H, dd, <sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.7 Hz, <sup>4</sup>J (H<sup>6</sup>H<sup>4</sup>) = 1.5 Hz, H<sup>6</sup>), 7.87 (1 H,
overlapping m, H<sup>4</sup>), 7.83 (1 H, overlapping t, <sup>3</sup><italic toggle="yes">J</italic> = 7.7 Hz, <italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>),
7.58 (1 H, d, <sup>3</sup>J (H<sup>3</sup>H<sup>4</sup>) = 8.1 Hz, H<sup>3</sup>), 7.31 (2 H, broad s, <italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>),
7.10 (1 H, apparent t, apparent <italic toggle="yes">J</italic> = 6.0 Hz, H<sup>5</sup>), 7.03 (2 H, d, <sup>3</sup><italic toggle="yes">J</italic> = 5.7
Hz, <italic toggle="yes">m</italic>-C<sub>6</sub><italic toggle="yes">H</italic><sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 6.68 (1 H, t, <sup>3</sup><italic toggle="yes">J</italic> = 7.7 Hz, <italic toggle="yes">p</italic>-C<sub>6</sub><italic toggle="yes">H</italic><sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 4.96 (1 H,
broad septet, <sup>3</sup><italic toggle="yes">J</italic> = 6.7 Hz, C<italic toggle="yes">H</italic>Me<sub>2</sub>), 4.01 (1 H, broad septet, <sup>3</sup><italic toggle="yes">J</italic> = 6.6
Hz, C<italic toggle="yes">H</italic>Me<sub>2</sub>), 3.74 (4 H, 4 x overlapping d, 2 x CH<sub>2</sub>), 1.55 (3 H, s, Me
of N<sub>2</sub>N<sub>py</sub>), 1.30 (6 H, 2 x broad overlapping d, CH<italic toggle="yes">Me</italic><sub>2</sub>), 1.20 (3 H, d,
<sup>3</sup><italic toggle="yes">J</italic> = 6.6 Hz, CH<italic toggle="yes">Me</italic><sub>2</sub>), 1.13 (3 H, d, <sup>3</sup><italic toggle="yes">J</italic> = 6.8 Hz, CH<italic toggle="yes">Me</italic><sub>2</sub>), −0.12 (9 H,
s, Si<italic toggle="yes">Me</italic><sub>3</sub>), −0.21 (9 H, s, SiMe<sub>3</sub>). <sup>13</sup>C-{<sup>1</sup>H} NMR (CD<sub>2</sub>Cl<sub>2</sub>, 75.5 MHz,
223 K): 164.2 (C<sup>2</sup>), 153.6 (<italic toggle="yes">o</italic>-NC<sub>5</sub>H<sub>5</sub>), 153.0 (<italic toggle="yes">ipso</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 150.0
(C<sup>6</sup>), 145.5 (<italic toggle="yes">o</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 142.8 (<italic toggle="yes">o</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 139.3 (C<sup>4</sup>), 139.3
(<italic toggle="yes">p</italic>-NC<sub>5</sub>H<sub>5</sub>), 124.4 (<italic toggle="yes">m</italic>-NC<sub>5</sub>H<sub>5</sub>), 123.2 (<italic toggle="yes">m</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 122.3 (<italic toggle="yes">m</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 121.6 (C<sup>5</sup>), 120.3 (<italic toggle="yes">p</italic>-2,6-C<sub>6</sub>H<sub>3</sub><italic toggle="yes"><sup>i</sup></italic><sup></sup>Pr<sub>2</sub>), 119.4 (C<sup>3</sup>), 62.4 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 61.0 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 50.7 (<italic toggle="yes">C</italic>(CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub>, 27.2 (<italic toggle="yes">C</italic>HMe<sub>2</sub>),
26.3 (<italic toggle="yes">C</italic>HMe<sub>2</sub>), 26.3 (CH<italic toggle="yes">Me</italic><italic toggle="yes"><sub>2</sub></italic>), 26.1 (CH<italic toggle="yes">Me</italic><italic toggle="yes"><sub>2</sub></italic>), 25.1 (CH<italic toggle="yes">Me</italic><italic toggle="yes"><sub>2</sub></italic>), 24.0 (Me
of N<sub>2</sub>N<sub>py</sub>), 23.7 (CH<italic toggle="yes">Me</italic><italic toggle="yes"><sub>2</sub></italic>), 0.6 (SiMe<sub>3</sub>), 0.3 (SiMe<sub>3</sub>). IR (CsBr plates,
Nujol, cm<sup>-1</sup>): 1615 (m), 1604 (m), 1590 (m), 1574 (w), 1295 (m),
1246 (s), 1156 (w), 1042 (m), 1016 (m), 960 (m), 922 (s), 841 (s), 787
(m), 752 (m), 701 (w), 429 (w), 410 (w) cm<sup>-1</sup>. Anal. Found (calculated
for C<sub>32</sub>H<sub>51</sub>ClN<sub>5</sub>Si<sub>2</sub>Ta): C 48.8 (49.4), H 7.0 (6.6), N 8.8 (9.0)%.
</p><p><bold>[Nb(N</bold><bold><italic toggle="yes"><sup>t</sup></italic></bold><sup></sup><bold>Bu)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)] (5). </bold>[Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>2</bold>) (0.310 g,
0.53 mmol) was sublimed at 125 °C and 9 × 10<sup>-6</sup> mbar over 6 h to
provide analytically pure [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)] (<bold>5</bold>) as a pale yellow
solid. Yield: 0.078 g (25%). <sup>1</sup>H NMR (C<sub>6</sub>D<sub>6</sub>, 500.0 MHz, 298 K):
8.92 (1 H, dd, <sup>3</sup>J (H<sup>6</sup>H<sup>5</sup>) = 5.5 Hz, <sup>4</sup>J (H<sup>6</sup>H<sup>4</sup>) = 1.0 Hz, H<sup>6</sup>), 7.08 (1 H,
dd, <sup>3</sup>J (H<sup>4</sup>H<sup>5</sup>) = 8.0 Hz, <sup>3</sup>J (H<sup>4</sup>H<sup>3</sup>) = 8.0 Hz, H<sup>4</sup>), 6.71 (1 H, d, <sup>3</sup>J
(H<sup>3</sup>H<sup>4</sup>) = 8.0 Hz, H<sup>3</sup>), 6.51 (1 H, apparent t, apparent <italic toggle="yes">J</italic> = 6.7 Hz, H<sup>5</sup>),
4.13 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5 Hz, CH<sub>2</sub>), 3.23 (2 H, d, <sup>2</sup><italic toggle="yes">J</italic> = 12.5, CH<sub>2</sub>), 1.59
(9 H, s, <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu), 0.91 (3 H, s, Me of N<sub>2</sub>N<sub>py</sub>), 0.07 (18 H, s, SiMe<sub>3</sub>). <sup>13</sup>C-{<sup>1</sup>H} NMR (C<sub>6</sub>D<sub>6</sub>, 125.7 MHz, 298 K): 159.8 (C<sup>2</sup>), 149.1 (C<sup>6</sup>), 138.2
(C<sup>4</sup>), 121.2 (C<sup>5</sup>), 120.7 (C<sup>3</sup>), 63.1 (<italic toggle="yes">C</italic>H<sub>2</sub>NSiMe<sub>3</sub>), 46.8 (<italic toggle="yes">C</italic>(CH<sub>2</sub>NSiMe<sub>3</sub>)<sub>2</sub>),
33.3 (NC<italic toggle="yes">Me</italic><sub>3</sub>), 23.8 (Me of N<sub>2</sub>N<sub>py</sub>), 0.5 (SiMe<sub>3</sub>), not observed: N<italic toggle="yes">C</italic>Me<sub>3</sub>.
IR (NaCl plates, Nujol, cm<sup>-1</sup>): 1600 (s), 1572 (w), 1358 (s), 1341
(m), 1281 (m), 1245 (s), 1233 (s), 1213 (s), 1157 (w), 1142 (m), 1132
(m), 1116 (m), 1084 (w), 1052 (s), 1048 (s), 1033 (s), 1001 (m), 951
(m), 899 (s), 874 (s), 838 (s), 800 (m), 778 (s), 725 (w), 686 (w), 599
(m), 520 (w), 493 (w), 439 (w) cm<sup>-1</sup>. Anal. Found (calculated for
C<sub>19</sub>H<sub>38</sub>ClN<sub>4</sub>NbSi<sub>2</sub>): C 45.0 (45.0), H 7.6 (7.6), N 11.1 (11.1)%.
</p><p><bold>Crystal structure determination of V(NAr)Cl</bold><bold><sub>2</sub></bold><bold>(H</bold><bold><sub>3</sub></bold><bold>N</bold>‘<bold>N</bold>‘ ‘<bold>N</bold><bold><sub>py</sub></bold><bold>)] (1),
[Nb(N</bold><bold><italic toggle="yes"><sup>t</sup></italic></bold><sup></sup><bold>Bu)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)] </bold><bold>(2), [Ta(N</bold><bold><italic toggle="yes"><sup>t</sup></italic></bold><sup></sup><bold>Bu)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)]</bold><bold></bold><bold>(3), and [Ta(NAr)Cl(N</bold><bold><sub>2</sub></bold><bold>N</bold><bold><sub>py</sub></bold><bold>)(py)] </bold><bold></bold><bold>(4). </bold>Crystal data collection and processing
parameters are given in Table <xref rid="ic0102541t00001"></xref>. Crystals were mounted in a film of
RS3000 perfluoropolyether oil (Hoechst) on a glass fiber and transferred
to a Stoë Stadi-4 four-circle diffractometer equipped with an Oxford
Cryosystems low-temperature device.<xref rid="ic0102541b00024" ref-type="bibr"></xref> Data were collected using ω−θ
scans with Mo Kα radiation (<italic toggle="yes">λ</italic> = 0.71073 Å), and absorption and decay
corrections were applied to the data as appropriate. Data for <bold>3</bold> were
collected on two individual crystals and were scaled and combined.
Equivalent reflections were merged, and the structures were solved by
direct methods (SIR92<xref rid="ic0102541b00025" ref-type="bibr"></xref> or SHELXS-96<xref rid="ic0102541b00026" ref-type="bibr"></xref>). Subsequent difference
Fourier syntheses revealed the positions of all other non-hydrogen
atoms. Structures were refined against <italic toggle="yes">F</italic> or <italic toggle="yes">F</italic><sup>2</sup> using a weighting scheme
where appropriate. Corrections for secondary extinction effects were
made as necessary.
<table-wrap id="ic0102541t00001" position="float" orientation="portrait"><label>1</label><caption><p>X-ray Data Collection and Processing Parameters for [V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>P</sub><sub>y</sub>) (<bold>1</bold>), [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>2</bold>),
[Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>3</bold>), and [Ta(NAr)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>4</bold>)</p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="5"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:colspec colnum="5" colname="5"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry namest="1" nameend="1"></oasis:entry><oasis:entry namest="2" nameend="2"><bold>1</bold></oasis:entry><oasis:entry namest="3" nameend="3"><bold>2</bold></oasis:entry><oasis:entry namest="4" nameend="4"><bold>3</bold></oasis:entry><oasis:entry namest="5" nameend="5"><bold>4</bold></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">empirical formula
</oasis:entry><oasis:entry colname="2">C<sub>27</sub>H<sub>46</sub>Cl<sub>2</sub>N<sub>4</sub>SiV
</oasis:entry><oasis:entry colname="3">C<sub>24</sub>H<sub>43</sub>ClN<sub>5</sub>NbSi<sub>2</sub></oasis:entry><oasis:entry colname="4">C<sub>24</sub>H<sub>43</sub>ClN<sub>5</sub>Si<sub>2</sub>Ta
</oasis:entry><oasis:entry colname="5">C<sub>32</sub>H<sub>51</sub>ClN<sub>5</sub>Si<sub>2</sub>Ta
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">fw
</oasis:entry><oasis:entry colname="2">576.63
</oasis:entry><oasis:entry colname="3">586.17
</oasis:entry><oasis:entry colname="4">674.21
</oasis:entry><oasis:entry colname="5">778.37
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">temp/°C
</oasis:entry><oasis:entry colname="2">−123(2)
</oasis:entry><oasis:entry colname="3">−123(2)
</oasis:entry><oasis:entry colname="4">−123(2)
</oasis:entry><oasis:entry colname="5">−123(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">wavelength/Å
</oasis:entry><oasis:entry colname="2">0.71073
</oasis:entry><oasis:entry colname="3">0.71073
</oasis:entry><oasis:entry colname="4">0.71073
</oasis:entry><oasis:entry colname="5">0.71073
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">space group
</oasis:entry><oasis:entry colname="2"><italic toggle="yes">Pbca</italic>
</oasis:entry><oasis:entry colname="3"><italic toggle="yes">Pbca</italic></oasis:entry><oasis:entry colname="4"><italic toggle="yes">Pbca</italic></oasis:entry><oasis:entry colname="5">P1̄
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">a</italic>/Å
</oasis:entry><oasis:entry colname="2">14.90(2)
</oasis:entry><oasis:entry colname="3">15.586(4)
</oasis:entry><oasis:entry colname="4">15.560(5)
</oasis:entry><oasis:entry colname="5">10.631(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">b</italic>/Å
</oasis:entry><oasis:entry colname="2">16.834(9)
</oasis:entry><oasis:entry colname="3">16.593(4)
</oasis:entry><oasis:entry colname="4">16.571(4)
</oasis:entry><oasis:entry colname="5">10.968(3)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">c</italic>/Å
</oasis:entry><oasis:entry colname="2">24.025(13)
</oasis:entry><oasis:entry colname="3">22.303(7)
</oasis:entry><oasis:entry colname="4">22.319(6)
</oasis:entry><oasis:entry colname="5">16.225(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">α/deg
</oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry colname="3"></oasis:entry><oasis:entry colname="4"></oasis:entry><oasis:entry colname="5">94.62(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">β/deg
</oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry colname="3"></oasis:entry><oasis:entry colname="4"></oasis:entry><oasis:entry colname="5">96.77(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">γ/deg
</oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry colname="3"></oasis:entry><oasis:entry colname="4"></oasis:entry><oasis:entry colname="5">106.06(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">V</italic>/Å<sup>3</sup></oasis:entry><oasis:entry colname="2">6026(1)
</oasis:entry><oasis:entry colname="3">5768(2)
</oasis:entry><oasis:entry colname="4">5755(3)
</oasis:entry><oasis:entry colname="5">1792.6(5)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">Z</italic></oasis:entry><oasis:entry colname="2">2
</oasis:entry><oasis:entry colname="3">8
</oasis:entry><oasis:entry colname="4">8
</oasis:entry><oasis:entry colname="5">2
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"><italic toggle="yes">d</italic> (calcd)/Mg·m<sup>-3</sup></oasis:entry><oasis:entry colname="2">1.27
</oasis:entry><oasis:entry colname="3">1.350
</oasis:entry><oasis:entry colname="4">1.556
</oasis:entry><oasis:entry colname="5">1.44
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">abs coeff/mm<sup>-</sup></oasis:entry><oasis:entry colname="2">0.56
</oasis:entry><oasis:entry colname="3">0.61
</oasis:entry><oasis:entry colname="4">4.017
</oasis:entry><oasis:entry colname="5">3.240
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">R indices [<italic toggle="yes">I </italic>> 2σ(<italic toggle="yes">I</italic>)]<italic toggle="yes"><sup>a</sup></italic><sup></sup></oasis:entry><oasis:entry colname="2"><italic toggle="yes">R</italic><sub>1</sub> = 0.099,
</oasis:entry><oasis:entry colname="3"><italic toggle="yes">R</italic><sub>1</sub> = 0.0605,
</oasis:entry><oasis:entry colname="4"><italic toggle="yes">R</italic><sub>1</sub> = 0.0526,
</oasis:entry><oasis:entry colname="5"><italic toggle="yes">R</italic><sub>1</sub> = 0.0426,
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"><italic toggle="yes">wR</italic><sub>2</sub> = 0.125
</oasis:entry><oasis:entry colname="3"><italic toggle="yes">Rw</italic> = 0.0654
</oasis:entry><oasis:entry colname="4"><italic toggle="yes">wR</italic><sub>2</sub> = 0.1215
</oasis:entry><oasis:entry colname="5"><italic toggle="yes">Rw</italic> = 0.0500
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">R indices (all data − for</oasis:entry><oasis:entry colname="2"><italic toggle="yes">R</italic><sub>1</sub> = 0.151,
</oasis:entry><oasis:entry colname="3"></oasis:entry><oasis:entry colname="4"><italic toggle="yes">R</italic><sub>1</sub> = 0.0734,
</oasis:entry><oasis:entry colname="5"></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">refinement on <italic toggle="yes">F</italic><sup>2</sup> only)<italic toggle="yes"><sup>a</sup></italic><sup></sup></oasis:entry><oasis:entry colname="2"><italic toggle="yes">wR</italic><sub>2</sub> = 0.161
</oasis:entry><oasis:entry colname="3"></oasis:entry><oasis:entry colname="4"><italic toggle="yes">wR</italic><sub>2</sub> = 0.1446
</oasis:entry><oasis:entry colname="5"></oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table><table-wrap-foot><p><italic toggle="yes"><sup>a</sup></italic><sup></sup> <italic toggle="yes">R</italic><sub>1</sub> = ∑||<italic toggle="yes">F</italic><sub>o</sub>| − |<italic toggle="yes">F</italic><sub>c</sub>||/∑|<italic toggle="yes">F</italic><sub>o</sub>|; <italic toggle="yes">wR</italic><sub>2</sub> = √{∑<italic toggle="yes">w </italic>(<italic toggle="yes">F</italic><sub>o</sub><sup>2</sup> − <italic toggle="yes">F</italic><sub>c</sub><sup>2</sup>)<sup>2</sup>/∑(<italic toggle="yes">w</italic>(<italic toggle="yes">F</italic><sub>o</sub><sup>2</sup>)<sup>2</sup>}; <italic toggle="yes">R</italic><sub>w</sub> = √{∑<italic toggle="yes">w </italic>(|<italic toggle="yes">F</italic><sub>o</sub>| − |<italic toggle="yes">F</italic><sub>c</sub>|)<sup>2</sup>/∑(<italic toggle="yes">w</italic>|<italic toggle="yes">F</italic><sub>o</sub>|<sup>2</sup>}.</p></table-wrap-foot></table-wrap></p><p>The crystal of <bold>1 </bold>was a very weak diffractor with mean <italic toggle="yes">I</italic>/σ = 4.79,
and hence data were collected only to θ<sub>max</sub> = 22.5°. The refinement
proceeded satisfactorily on 3467 data with (<italic toggle="yes">I</italic>/σ) > 0 subject to similarity
restraints on the C(quaternary)−C(methyl) distances for the <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu group
C(24)−C(28) and general vibrational restraints on the displacement
parameters of the non-H atoms. For all four structures, H atoms bound
to carbon were placed in calculated positions and refined in riding
models. For <bold>1</bold> the H atoms attached to N(2) and N(4) were located
from difference maps and were positionally refined subject to similarity
restraints on the N−H distances. The largest peaks and holes in the
final Fourier difference syntheses of the tantalum structures <bold>3</bold> and <bold>4
</bold>lie less than ca. 1 Å from Ta(1); for <bold>1</bold> the largest peaks were located
at 1.54 and 1.40 Å from V(1) and Cl(1), respectively. In all three
structures these final peaks and holes are attibuted to residual absorption
artifacts.
</p><p>Crystallographic calculations were performed using SIR92,<xref rid="ic0102541b00025" ref-type="bibr"></xref> SHELXS-96,<xref rid="ic0102541b00026" ref-type="bibr"></xref> SHELXL-96,<xref rid="ic0102541b00027" ref-type="bibr"></xref> or CRYSTALS.<xref rid="ic0102541b00028" ref-type="bibr"></xref> A full listing of atomic
coordinates, bond lengths and angles, and displacement parameters for
<bold>1</bold>−<bold>4</bold> have been deposited at the Cambridge Crystallographic Data
Center. See Notice to Authors, Issue No. 1.
</p></sec><sec id="d7e3457"><title>Results and Discussion</title><p>Initial efforts focused on attempts to prepare vanadium(V)
complexes of diamido-pyridine ligands N<sub>2</sub>N<sub>py</sub> or N‘<sub>2</sub>N<sub>py</sub> by
reaction of the previously described arylimido complex [V(NAr)Cl<sub>3</sub>(THF)]<sup>23</sup> with M<sub>2</sub>N<sub>2</sub>N<sub>py</sub> or M<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub> (M = H or Li).
Reactions with dilithium derivatives of the diamido-pyridines
gave uncharacterized mixtures, and only the reaction of
[V(NAr)Cl<sub>3</sub>(THF)] with the ligand precursor H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub> in cold
Et<sub>2</sub>O in the presence of Et<sub>3</sub>N gave any isolable product at all
(eq 1). Under these conditions the vanadium(IV) compound
[V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>py</sub>)] [<bold>1</bold>, H<sub>3</sub>N‘N‘ ‘N<sub>py</sub> = MeC(2-C<sub>5</sub>H<sub>4</sub>N)(CH<sub>2</sub>NHSiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)(CH<sub>2</sub>NH<sub>2</sub>)] can be isolated in 12% yield. Attempts
to identify any other metal-containing products of this reaction
were unsuccessful. Nonetheless, the compound <bold>1</bold> was reproducibly generated, either as red-brown crystals or as a red-brown
powder, in similar yields.
<fig id="ic0102541f2" position="float" orientation="portrait"><label></label><graphic xlink:href="ic0102541f2.tif" position="float" orientation="portrait"></graphic></fig></p><p>The solid-state X-ray structure of [V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>py</sub>)]
(<bold>1</bold>) is shown in Figures <xref rid="ic0102541f00001"></xref>a and <xref rid="ic0102541f00001"></xref>b; selected bond lengths and
angles are presented in Table <xref rid="ic0102541t00002"></xref>. The crystal of <bold>1 </bold>was a very
weak diffractor but nonethless a full anisotropic refinement of
all non-H atoms was possible (subject to vibrational restraints).
The H atoms bound the amino nitrogens N(2) and N(4) were
located from Fourier difference syntheses and positionally
refined.
<fig id="ic0102541f00001" position="float" orientation="portrait"><label>1</label><caption><p>Molecular structure plots of [V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>py</sub>)] (<bold>1</bold>)
with carbon-bound H atoms omitted: (a) view of the monomeric unit
with displacement ellipsoids drawn at the 40% probability level and
N-bound H atoms drawn as spheres of an arbitary radius; (b) ball-and-stick plot of the hydrogen-bonded dimer in which atoms carrying the
suffix “A” are related to their counterparts by the symmetry operator
[−<italic toggle="yes">x</italic> + 1, −<italic toggle="yes">y</italic>, −<italic toggle="yes">z</italic> + 2].</p></caption><graphic xlink:href="ic0102541f00001.tif" position="float" orientation="portrait"></graphic></fig><table-wrap id="ic0102541t00002" position="float" orientation="portrait"><label>2</label><caption><p>Selected Bond Lengths (Å) and Angles (deg) for [V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>P</sub><sub>y</sub>)] (<bold>1</bold>)<italic toggle="yes"><sup>a</sup></italic><sup></sup></p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="4"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry namest="1" nameend="1">distances</oasis:entry><oasis:entry namest="2" nameend="2"></oasis:entry><oasis:entry namest="3" nameend="3">angles</oasis:entry><oasis:entry namest="4" nameend="4"></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−N(1)
</oasis:entry><oasis:entry colname="2">1.685(8)
</oasis:entry><oasis:entry colname="3">V(1)−N(1)−C(1)
</oasis:entry><oasis:entry colname="4">173.2(8)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−N(2)
</oasis:entry><oasis:entry colname="2">2.143(9)
</oasis:entry><oasis:entry colname="3">N(1)−V(1)−N(2)
</oasis:entry><oasis:entry colname="4">93.3(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−N(3)
</oasis:entry><oasis:entry colname="2">2.136(9)
</oasis:entry><oasis:entry colname="3">N(1)−V(1)−N(3)
</oasis:entry><oasis:entry colname="4">96.9(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−N(4)
</oasis:entry><oasis:entry colname="2">2.475(9)
</oasis:entry><oasis:entry colname="3">N(1)−V(1)−N(4)
</oasis:entry><oasis:entry colname="4">168.7(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−Cl(1)
</oasis:entry><oasis:entry colname="2">2.374(4)
</oasis:entry><oasis:entry colname="3">N(1)−V(1)−Cl(2)
</oasis:entry><oasis:entry colname="4">97.9(3)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">V(1)−Cl(2)
</oasis:entry><oasis:entry colname="2">2.416(4)
</oasis:entry><oasis:entry colname="3">N(1)−V(1)−Cl(2)
</oasis:entry><oasis:entry colname="4">99.3(3)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−C(1)
</oasis:entry><oasis:entry colname="2">1.38(1)
</oasis:entry><oasis:entry colname="3">N(2)−V(1)-N(3)
</oasis:entry><oasis:entry colname="4">88.8(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">Cl(2)···H(2A)
</oasis:entry><oasis:entry colname="2">2.31(3)
</oasis:entry><oasis:entry colname="3">Cl(1)−V(1)−Cl(2)
</oasis:entry><oasis:entry colname="4">93.5(1)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry colname="3">V(1)−Cl(2) ···H(2A)
</oasis:entry><oasis:entry colname="4">132(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"></oasis:entry><oasis:entry colname="3">N(2)−H(2)···Cl(2A)
</oasis:entry><oasis:entry colname="4">169(7)</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table><table-wrap-foot><p><italic toggle="yes"><sup>a</sup></italic><sup></sup> Atoms carrying the suffix “A” are related to their counterparts by
the symmetry operator [−<italic toggle="yes">x</italic> + 1, −<italic toggle="yes">y</italic>, −<italic toggle="yes">z</italic> + 2].</p></table-wrap-foot></table-wrap></p><p>The X-ray structure of the monomeric unit of <bold>1</bold> (Figure <xref rid="ic0102541f00001"></xref>a)
confirms how the H<sub>2</sub>N‘<sub>2</sub>N<sub>py</sub> ligand has been substantially altered,
with one “arm” still bearing a SiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu substituent but with
the other having lost this group which has been formally
replaced by a hydrogen atom. Together with the presence of a
V(IV) center in <bold>1</bold>, this feature is probably indicative of redox
reactions taking place during the reaction. The remaining three
coordination sites about vanadium are occupied by the arylimido
ligand and by a pair of mutually cis disposed chloride ligands.
The VN<sub>(imide)</sub> distance of 1.685(8) Å is typical for terminal
vanadium arylimides (seven examples with VN distances
ranging from 1.615 to 1.730 Å, average 1.693 Å),<xref rid="ic0102541b00029" ref-type="bibr"></xref> although it
is slightly shorter than the typical range for specifically V(IV)N<sub>(imide)</sub> bonds (1.707−1.730 Å for three examples). The V−Cl
bond distances are unremarkable.
</p><p>As mentioned, the hydrogen atoms of the amine donors were
located from Fourier difference maps. The V−N(2) bond
distance of 2.143(9) Å is typical of V−N<sub>(amine)</sub> linkages, while
the V−N(4) distance of 2.475(9) Å is unusually long, probably
due to the strong <italic toggle="yes">trans</italic>-influence of the imido ligand and the
large steric bulk of the dimethyl-<italic toggle="yes">tert</italic>-butylsilyl substituent.
Interestingly, molecules of <bold>1</bold> form centrosymmetric, hydrogen-bonded dimers in the solid state, in the manner shown in Figure
<xref rid="ic0102541f00001"></xref>b. The hydrogen bonds occur between Cl(2) and H(2A) and
between H(2) and Cl(2A). Recent work by Brammer, Orpen,
and co-workers has highlighted the widespread occurrence of
such M-Cl···H−N bonds in the solid state,<xref rid="ic0102541b00030" ref-type="bibr"></xref> and the Cl(2)···
H(2A) distance of 2.31(3) Å is very close to the median value
found for such contacts. It was not possible to establish if
molecules of <bold>1</bold> possess a hydrogen-bonded structure in the
solution state too since <bold>1</bold> is soluble only in donor solvents such
as Et<sub>2</sub>O and thf, which would be expected to disrupt any weakly
N−H···Cl bonded dimeric structure.
</p><p>The solid-state structure found by X-ray crystallography is
supported by elemental combustion analysis, IR, EPR and NMR
spectroscopy, and mass spectromtery. In accordance with the
d<sup>1</sup> metal center in <bold>1</bold>, no signals for the complex itself were
visible in the <sup>1</sup>H NMR spectrum in the range +30 to −30 ppm.
<sup>1</sup>H NMR studies of the reaction mixture nonetheless proved
useful, showing signals assigned to ClSiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu, consistent with
the loss of a SiMe<sub>2</sub><italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu substituent from H<sub>2</sub>N<sub>2</sub>‘N<sub>py</sub> and of a
chloride ligand from vanadium. The IR spectrum of <bold>1</bold> as a Nujol
mull revealed three sharp peaks at 3349, 3236, and 3158 cm<sup>-1</sup>.
Similar absorptions have not been observed in any other metal
compound of the N<sub>2</sub>N<sub>py</sub> or N‘<sub>2</sub>N<sub>py</sub> ligands. These bands lie in
the expected region for N−H stretches and are attributed to the
amine hydrogen atoms. The room-temperature EPR spectrum
of <bold>1</bold> in thf solution exhibits the expected eight (2<italic toggle="yes">I</italic> + 1) peaks
consistent with a metal-based electron coupling to a quadrupolar
vanadium nucleus of nuclear spin <italic toggle="yes">I</italic> = <sup>7</sup>/<sub>2</sub>. With values of <italic toggle="yes">g </italic>=
1.982 and <italic toggle="yes">A </italic>= 90.9 G, the 298 K <italic toggle="yes">g</italic>-factor and hyperfine
coupling parameter are in good agreement with literature values
reported for other V(IV) compounds.<named-content content-type="bibref-group"><xref rid="ic0102541b00031" ref-type="bibr"></xref>−<xref rid="ic0102541b00032" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00033" ref-type="bibr"></xref></named-content></p><p>Because of the low yields and ligand degradation associated
with the formation of [V(NAr)Cl<sub>2</sub>(H<sub>3</sub>N‘N‘ ‘N<sub>py</sub>)] (<bold>1</bold>), we turned
our attention to the synthesis of N<sub>2</sub>N<sub>py</sub> derivatives of the heavier
Group 5 congeners. These metals are typically more resistant
to redox processes in their M(V) oxidation states than is
vanadium. High-yielding syntheses of Group 4 imido complexes
of the N<sub>2</sub>N<sub>py</sub> (<bold>I</bold> and <bold>II</bold>, Chart <xref rid="ic0102541c00001"></xref>) and N<sub>2</sub>N<sub>am</sub> (<bold>III</bold>, Chart <xref rid="ic0102541c00001"></xref>) ligands
were previously achieved from the reaction of metal imide-containing precursors and the dilithium compounds Li<sub>2</sub>N<sub>2</sub>N<sub>py</sub>
or Li<sub>2</sub>N<sub>2</sub>N<sub>am</sub>.<xref rid="ic0102541b00010" ref-type="bibr"></xref> Similar routes have been employed in the present
work starting from the known<sup>21,22</sup> imido-niobium and -tantalum
compounds [M(NR)Cl<sub>3</sub>(py)<sub>2</sub>] (M = Nb or Ta, R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu or Ar)
and Li<sub>2</sub>N<sub>2</sub>N<sub>py</sub> in cold benzene solution. The new compounds
[M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (M = Nb, R = <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu <bold>2</bold>; M = Ta, R =
N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu <bold>3</bold> or Ar <bold>4</bold>) were isolated in fair to good yields, and the
reactions are summarized in eq 2.
<fig id="ic0102541f3" position="float" orientation="portrait"><label></label><graphic xlink:href="ic0102541f3.tif" position="float" orientation="portrait"></graphic></fig></p><p>All three compounds <bold>2</bold>−<bold>4 </bold>have been crystallographically
characterized. For ease of comparison, views of the three
structures are collected together in Figures <xref rid="ic0102541f00002"></xref>a−c; selected bond
lengths and angles are compiled in Table <xref rid="ic0102541t00003"></xref>. We shall discussthe
three structures together as they form a closely linked series in
which the effects of changing the metal from Nb (in <bold>2</bold>) to Ta
(in <bold>3</bold>), and then changing the imide N-substituent from <italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu (in
<bold>3</bold>) to Ar (in <bold>4</bold>), can be specifically traced.
<fig id="ic0102541f00002" position="float" orientation="portrait"><label>2</label><caption><p>Displacement ellipsoid plots with hydrogen atoms are omitted and ellipsoids drawn at the 45% (<bold>2</bold>, <bold>3</bold>) or 35% (<bold>4</bold>) probability level: (a)
[Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>2</bold>); (b) [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>3</bold>); (c) [Ta(NAr)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>4</bold>).</p></caption><graphic xlink:href="ic0102541f00002.tif" position="float" orientation="portrait"></graphic></fig><table-wrap id="ic0102541t00003" position="float" orientation="portrait"><label>3</label><caption><p>Selected Bond Lengths (Å) and Angles (deg) for [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>2</bold>), [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>3</bold>), and
[Ta(NAr)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (<bold>4</bold>)</p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="4"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry namest="1" nameend="1">parameter</oasis:entry><oasis:entry namest="2" nameend="2"><bold>2</bold> (M = Nb)</oasis:entry><oasis:entry namest="3" nameend="3"><bold>3</bold> (M = Ta)</oasis:entry><oasis:entry namest="4" nameend="4"><bold>4</bold> (M = Ta)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(1)
</oasis:entry><oasis:entry colname="2">1.781(6)
</oasis:entry><oasis:entry colname="3">1.793(7)
</oasis:entry><oasis:entry colname="4">1.822(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(2)
</oasis:entry><oasis:entry colname="2">2.040(6)
</oasis:entry><oasis:entry colname="3">2.043(7)
</oasis:entry><oasis:entry colname="4">2.036(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(3)
</oasis:entry><oasis:entry colname="2">2.044(6)
</oasis:entry><oasis:entry colname="3">2.023(8)
</oasis:entry><oasis:entry colname="4">2.004(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(4)
</oasis:entry><oasis:entry colname="2">2.428(5)
</oasis:entry><oasis:entry colname="3">2.409(7)
</oasis:entry><oasis:entry colname="4">2.397(5)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(5)
</oasis:entry><oasis:entry colname="2">2.407(6)
</oasis:entry><oasis:entry colname="3">2.370(7)
</oasis:entry><oasis:entry colname="4">2.356(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−Cl(1)
</oasis:entry><oasis:entry colname="2">2.548(2)
</oasis:entry><oasis:entry colname="3">2.518(2)
</oasis:entry><oasis:entry colname="4">2.518(1)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−C(1)
</oasis:entry><oasis:entry colname="2">1.464(9)
</oasis:entry><oasis:entry colname="3">1.443(11)
</oasis:entry><oasis:entry colname="4">1.372(7)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">M(1)−N(1)−C(1)
</oasis:entry><oasis:entry colname="2">166.1(5)
</oasis:entry><oasis:entry colname="3">167.3(6)
</oasis:entry><oasis:entry colname="4">176.6(4)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−M(1)−N(2)
</oasis:entry><oasis:entry colname="2">104.2(2)
</oasis:entry><oasis:entry colname="3">104.2(3)
</oasis:entry><oasis:entry colname="4">103.6(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−M(1)−N(3)
</oasis:entry><oasis:entry colname="2">106.8(2)
</oasis:entry><oasis:entry colname="3">107.8(3)
</oasis:entry><oasis:entry colname="4">104.3(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−M(1)−N(4)
</oasis:entry><oasis:entry colname="2">166.4(2)
</oasis:entry><oasis:entry colname="3">166.3(3)
</oasis:entry><oasis:entry colname="4">171.1(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−M(1)−N(5)
</oasis:entry><oasis:entry colname="2">92.3(2)
</oasis:entry><oasis:entry colname="3">92.9(3)
</oasis:entry><oasis:entry colname="4">96.4(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(1)−M(1)−Cl(1)
</oasis:entry><oasis:entry colname="2">91.8(2)
</oasis:entry><oasis:entry colname="3">92.1(2)
</oasis:entry><oasis:entry colname="4">94.7(1)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(2)−M(1)−N(3)
</oasis:entry><oasis:entry colname="2">92.1(2)
</oasis:entry><oasis:entry colname="3">91.9(3)
</oasis:entry><oasis:entry colname="4">95.0(2)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">N(5)−M(1)−Cl(1)
</oasis:entry><oasis:entry colname="2">81.6(1)
</oasis:entry><oasis:entry colname="3">82.38(17)
</oasis:entry><oasis:entry colname="4">80.7(1)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">sum of the angles
subtended at N(3)
</oasis:entry><oasis:entry colname="2">358(1)
</oasis:entry><oasis:entry colname="3">359(1)
</oasis:entry><oasis:entry colname="4">360(1)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">sum of angles
subtended at N(3)
</oasis:entry><oasis:entry colname="2">355(1)
</oasis:entry><oasis:entry colname="3">354(2)
</oasis:entry><oasis:entry colname="4">359(1)</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table></table-wrap></p><p>The compounds <bold>2</bold>−<bold>4</bold> are the first crystallographically characterized examples of a terminal niobium or tantalum imides
supported by a diamide ligand, although monoamide-supported
examples such as [Nb(NAr)(NMe<sub>2</sub>)<sub>3</sub>]<sup>34</sup> and [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>]<sup>35</sup> are known. They all feature approximately
octahedral metal centers with a near-linear organoimido ligand
in one of the axial positions. The angles subtended at the imido
nitrogen [166.1(5) ≤ C(1)−N<sub>(imide)</sub>−M ≤ 176.6(4)°] show that
the imide can in principle act as four-electron donor.<named-content content-type="bibref-group"><xref rid="ic0102541b00003" ref-type="bibr"></xref>,<xref rid="ic0102541b00036" ref-type="bibr"></xref>,<xref rid="ic0102541b00037" ref-type="bibr"></xref></named-content> The
N<sub>2</sub>N<sub>py</sub> ligand adopts a fac-κ<sup>3</sup> coordination mode as found in
most of its transition metal imido complexes to date.<xref rid="ic0102541b00008" ref-type="bibr"></xref> The
pyridyl moiety of N<sub>2</sub>N<sub>py</sub> lies approximately trans to the imido
nitrogen, and the Cl and pyridine ligands occupy mutually cis,
equatorial positions trans to the amide donors of N<sub>2</sub>N<sub>py</sub>. The
angles subtended at the metal between the imido nitrogen N(1)
and the donor atoms of the equatorial groups are all in excess
of the theoretical 90° expected for a regular octahedral geometry.
This is a typical consequence of the trans influence of ligands
multiply bonded to transition metals, and the likely electronic
and steric driving forces for such features have been dealt with
in detail elsewhere.<xref rid="ic0102541b00037" ref-type="bibr"></xref></p><p>At 1.781(6) Å, the NbN<sub>(imide)</sub> bond length in <bold>2</bold> is at the
long end of the range for alkylimido linkages (range: 1.744(3)−1.789(4) Å for eight <italic toggle="yes">tert</italic>-butylimido complexes).<named-content content-type="bibref-group"><xref rid="ic0102541b00038" ref-type="bibr"></xref>−<xref rid="ic0102541b00039" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00040" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00041" ref-type="bibr"></xref></named-content> The
particularly long M=N<sub>(imide)</sub> bond in <bold>2</bold> (and also in <bold>3</bold> and <bold>4</bold>see below) is probably a result both of the steric pressure
between the imido <italic toggle="yes">tert</italic>-butyl group and the amido trimethylsilyl
substituents cis to it and of the presence of strong σ- and π-donor
amides in the equatorial positions. The Nb−Cl bond length of
2.548(2) Å is also unusually long, such bonds more commonly
lying in the range 2.35−2.45 Å.<xref rid="ic0102541b00029" ref-type="bibr"></xref> This presumably reflects a
mixture of steric crowding effects and the strong trans influence
of the strongly σ- and π-donating N<sub>2</sub>N<sub>py</sub> amide nitrogen donors.
Comparison of the Nb−N<sub>(pyridine)</sub> and Nb−N<sub>(pyridyl)</sub> bond lengths
indicates that the pyridine ligand is marginally more tightly
bound to the metal than the N<sub>2</sub>N<sub>py</sub> pyridyl group and, all other
factors aside, is consistent with the characteristic trans-bond
lengthening effect of imido ligands.<xref rid="ic0102541b00037" ref-type="bibr"></xref></p><p>Nearly all of the bond lengths and angles for complex <bold>3</bold> are
identical within experimental error to those of <bold>2</bold>, as would be
expected from the essentially idential atomic and ionic radii of
Nb and Ta.<xref rid="ic0102541b00042" ref-type="bibr"></xref> The most notable differences exist in the relative
bond lengths of M−N<sub>(pyridyl)</sub> [2.409(7) Å] and M−N<sub>(pyridine)</sub>
[2.370(7) Å], the pyridine ligand in this compound being
noticeably more tightly bound to the metal than the N<sub>2</sub>N<sub>py</sub>
pyridyl group. The long M−Cl bond distance of 2.548(2) Å in
<bold>2</bold> is shortened to 2.518(2) Å in <bold>3</bold>, although this still remains
very long for a terminal Ta−Cl bond, typical values lying nearer
to 2.40 Å.<xref rid="ic0102541b00029" ref-type="bibr"></xref> The TaN<sub>(imide)</sub> bond distance of 1.793(7) Å is
among the longest recorded for a tantalum terminal <italic toggle="yes">tert</italic>-butylimide, previous examples ranging from 1.61(3) Å to 1.78(2) Å.<named-content content-type="bibref-group"><xref rid="ic0102541b00035" ref-type="bibr"></xref>,<xref rid="ic0102541b00041" ref-type="bibr"></xref>,<xref rid="ic0102541b00043" ref-type="bibr"></xref>−<xref rid="ic0102541b00044" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00045" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00046" ref-type="bibr"></xref></named-content></p><p>The same structural motif as in compounds <bold>2</bold> and <bold>3</bold> appears
in [Ta(NAr)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>4</bold>). The TaN<sub>(imide)</sub> bond length of
1.822(4) Å is relatively long compared to those of many other
tantalum terminal arylimides, the TaN bond lengths of which
take values of less than 1.80 Å (1.769(5)-1.799(2) Å for nine
examples).<named-content content-type="bibref-group"><xref rid="ic0102541b00034" ref-type="bibr"></xref>,<xref rid="ic0102541b00038" ref-type="bibr"></xref>,<xref rid="ic0102541b00047" ref-type="bibr"></xref>−<xref rid="ic0102541b00048" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00049" specific-use="suppress-in-print" ref-type="bibr"></xref><xref rid="ic0102541b00050" ref-type="bibr"></xref></named-content> As in the tantalum <italic toggle="yes">tert</italic>-butylimido compound <bold>3</bold>, the pyridine ligand is more tightly bound to the metal
center than the N<sub>2</sub>N<sub>py</sub> pyridyl group. There is a lengthening of
the TaNAr bond in <bold>4</bold> compared to TaN<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu in <bold>3</bold>. With the
bulky <italic toggle="yes">iso</italic>-propyl ortho-substituents on Ar there is probably a
steric origin (at least in part) for this observation. However, a
recent comparison of homologous <italic toggle="yes">tert</italic>-butyl and aryl-imido
complexes have shown that the MN<sub>(imide)</sub> distances in the latter
group are, on average, significantly longer and the electronic
origins of this have been elucidated.<named-content content-type="bibref-group"><xref rid="ic0102541b00037" ref-type="bibr"></xref>,<xref rid="ic0102541b00051" ref-type="bibr"></xref></named-content> There is a general
shortening of the other Ta-ligand distances, consistent with the
reduced general labilizing effect of arylimides compared to <italic toggle="yes">tert</italic>-butylimides as previously recognized.<named-content content-type="bibref-group"><xref rid="ic0102541b00037" ref-type="bibr"></xref>,<xref rid="ic0102541b00051" ref-type="bibr"></xref></named-content></p><p>In the three compounds <bold>2</bold>−<bold>4</bold> the N<sub>2</sub>N<sub>py</sub> amide donor nitrogens
N(2) and N(3) are effectively planar [354(2) ≤ {sum of the
angles subtended at N(2,3)} ≤ 360(1)°] and so are presumably
sp<sup>2</sup> hybridized. Each amide nitrogen can therefore in principle
donate 3 electrons to the metal center, depending on the
orientation of the amide nitrogen 2p π-donor orbital and the
availability of the <italic toggle="yes">n</italic>d (<italic toggle="yes">n</italic> = 4 or 5) π-acceptor orbitals at metal.
For all the compounds the trigonal plane defined by the atoms
bonded to each amide nitrogen is twisted by between 46 and
61° out of coplanarity with the best-fit equatorial plane around
M as defined by the atoms {N(2), N(3), N(5), Cl(1)}. The effect
is to bring the SiMe<sub>3</sub> groups out of this equatorial plane and
“up” toward the imido ligands. By comparison, the equivalent
planes around the amide donors in the five-coordinate Group 4
complexes [M(NR)(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>I</bold>, Chart <xref rid="ic0102541c00001"></xref>) are much more
coplanar.<xref rid="ic0102541b00014" ref-type="bibr"></xref> Specifically for M = Zr and R = Ar the least squares
planes around the amide nitrogens are angled at only 22.4° and
27.5° from the least-squares equatorial plane around Zr.
</p><p>There are plausible steric and electronic reasons for the
orientation of the amido nitrogen substituents and lone pairs,
both operating in the same direction (i.e., that observed in the
three crystal structures). On steric grounds one might expect
the bulky SiMe<sub>3</sub> groups to move out of the equatorial plane to
minimize unfavorable interactions with the Cl and pyridine
ligands. Presumably there is a limit to how far the SiMe<sub>3</sub>
groups will be able to rotate before steric interactions with
the imido N-substituents inhibit further movemement. Indeed
the amido groups in <bold>4</bold> (with the bulkiest imido N-substituent)
are rotated by only 46° and 49° out of the equatorial plane
around Ta, as might be expected according to steric arguments.
</p><p>The electronic preferences for rotation of the amide groups
can be visualized with reference to Figure <xref rid="ic0102541f00003"></xref> which highlights
the various metal and nitrogen d<sub>π</sub> and p<sub>π</sub> acceptor/donor orbitals.
The complexes are taken as being (more or less) oriented with
the metal−ligand bonds along Cartesian coordinates and the
MN<sub>(imide)</sub> vector as being coincident with the <italic toggle="yes">z</italic> axis. In this
arrangement there are three σ nonbonding <italic toggle="yes">n</italic>d atomic orbitals at
the metal center available for d<sub>π</sub>−p<sub>π</sub> interactions (Figure <xref rid="ic0102541f00003"></xref>, <bold>E</bold>,
<bold>F</bold>, and <bold>G</bold>). These are the t<sub>2g</sub> set of orbitals in regular O<sub>h</sub>
symmetry, namely the <italic toggle="yes">n</italic>d(<italic toggle="yes">xz</italic>), <italic toggle="yes">n</italic>d(<italic toggle="yes">yz</italic>), and <italic toggle="yes">n</italic>d(<italic toggle="yes">xy</italic>) in the C<sub>1</sub>
symmetry of <bold>2</bold>−<bold>4</bold>. The metal <italic toggle="yes">n</italic>d(<italic toggle="yes">xz</italic>) and <italic toggle="yes">n</italic>d(<italic toggle="yes">yz</italic>) orbitals will be
used for interactions with the 2p(<italic toggle="yes">x</italic>) and 2p(<italic toggle="yes">y</italic>) π-donor orbitals
(<bold>C</bold> and <bold>D</bold> in Figure <xref rid="ic0102541f00003"></xref>) of the imido ligand (the shorter MN<sub>(imide)</sub> versus M−N<sub>(amide)</sub> bond length means that d<sub>π</sub>−p<sub>π</sub>
interactions of the former should take precedent on overlap
grounds<xref rid="ic0102541b00052" ref-type="bibr"></xref>). Therefore in the molecules <bold>2</bold>−<bold>4</bold> only the metal <italic toggle="yes">n</italic>d(<italic toggle="yes">xy</italic>) is available for N<sub>(amide)</sub>→M π-donation, and for this to occur
the appropriate amide p<sub>π</sub> lone pair donor orbital combination
(<bold>A</bold> in Figure <xref rid="ic0102541f00003"></xref>) clearly should lie in the <italic toggle="yes">x</italic><italic toggle="yes">−</italic><italic toggle="yes">y</italic> (equatorial) plane
(note that the anti-symmetric donor orbital linear combination
<bold>B</bold> has a node passing through M and so <bold>B</bold> will represent a
ligand-based nonbonding orbital). Rotating the amido groups
(i.e., the trigonal planes containing the amido nitrogens) out of
the equatorial plane will progressively bring the lone pairs into
alignment with the remaining <italic toggle="yes">n</italic>d(<italic toggle="yes">xy</italic>) π-acceptor orbital, thus
providing an electronic driving force for the features observed
in the crystal structures if <bold>2</bold>−<bold>4</bold>. It is clear from this description
that the amide nitrogens can act at best as only net 2 electron
donors (rather than as 3 electron donors which is in principle
possible according to their formal sp<sup>2</sup> hybridization) to the metal
center, which in turn possesses a formal valence electron count
of 18. A recent computational analysis of the metal−nitrogen
bonding in related ene-diamido d<sup>0</sup> metal complexes concurs with
the bonding scheme described here for <bold>2</bold>−<bold>4</bold>.<xref rid="ic0102541b00053" ref-type="bibr"></xref><fig id="ic0102541f00003" position="float" orientation="portrait"><label>3</label><caption><p>Linear combinations of amide 2p<sub>π</sub>-donor orbitals (<bold>A</bold>, <bold>B</bold>),
imide 2p<sub>π</sub>-donor orbitals (<bold>C</bold>, <bold>D</bold>) and metal based <italic toggle="yes">n</italic>d<sub>π</sub> (“t<sub>2g</sub>”) orbitals
(<bold>E</bold>, <bold>F</bold>, <bold>G</bold>) for [M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>2</bold>−<bold>4</bold>) with the orientation of the
amide 2p<sub>π</sub> donors idealized to lie in the equatorial plane.</p></caption><graphic xlink:href="ic0102541f00003.tif" position="float" orientation="portrait"></graphic></fig></p><p>The compounds <bold>2</bold>−<bold>4</bold> have been further characterized by
combustion elemental analysis and IR and NMR spectroscopy.
The low temperature (218−223 K) NMR spectra are consistent
with the solid-state structures shown in Figure <xref rid="ic0102541f00002"></xref>. In the <sup>1</sup>H NMR
spectra the SiMe<sub>3</sub> groups trans to Cl and pyridine, respectively,
appear as two individual singlets, while the CH<sub>2</sub> group protons
appear as two pairs of mutually coupled doublets. These features
are consistent with the absence of a molecular mirror plane in
the ground-state structures. The shifts for the ortho (H<sup>6</sup>) protons
of the N<sub>2</sub>N<sub>py</sub> pyridyl fragment are consistent with this group
being coordinated in solution. All three compounds are fluxional
at room temperature in solution. By way of example, the spectra
of only [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>2</bold>) will be specifically
discussed here.
</p><p>On warming an NMR sample of <bold>2</bold> in CD<sub>2</sub>Cl<sub>2</sub> from 218 to
268 K the two SiMe<sub>3</sub> group singlets initially broaden and
coalesce, and the two pairs of doublets (at 218 K) for the two
sets of diasterotopic CH<sub>2</sub> groups of N<sub>2</sub>N<sub>py</sub> broaden and give
rise to one pair of mutually coupled doublets (integrating as 2
× 2H). In the fast exchange limit the <sup>1</sup>H and <sup>13</sup>C NMR spectra
of <bold>2</bold> (and also of <bold>3</bold> and <bold>4</bold>) are consistent with the molecule
possessing effective <italic toggle="yes">C</italic><sub>s</sub> symmetry with a mirror plane (on the
NMR time scale) passing through the imido, M, and pyridyl
groups. A likely mechanism for the exchange process is shown
in eq 3. We propose that pyridine dissociates to form C<sub>s</sub>-symmetric [M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)] in which the SiMe<sub>3</sub> and CH<sub>2</sub>
groups can become equivalent; re-coordination of pyridine can
occur to give either the initial diasteromer or the mirror image
(at right in eq 3), the latter effecting the SiMe<sub>3</sub> and CH<sub>2</sub> group
exchange implied by the variable temperature NMR spectra.
The monomeric, trigonal bipyramidal structures assumed for
the intermediates [M(NR)Cl(N<sub>2</sub>N<sub>py</sub>)] (with the imido group in
the equatorial plane) are based on the known structures of the
isoelectronic Group 4 complexes <bold>I</bold> (Chart <xref rid="ic0102541c00001"></xref>) as well as for the
isolated intermediate [Nb(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)] (<bold>5</bold>see Equation 4).
However, the current results do not conclusively rule out an
alternative intermediate with the chloride ligand in the equatorial
plane and the imido group trans to pyridyl.
<fig id="ic0102541f4" position="float" orientation="portrait"><label></label><graphic xlink:href="ic0102541f4.tif" position="float" orientation="portrait"></graphic></fig></p><p>The compound <bold>5</bold> was obtained by careful high-vacuum (10<sup>-6</sup>
mbar) tube sublimation of <bold>2</bold>, and the orientation of the imido
group with respect to the other ligands was confirmed by nOe
(nuclear Overhauser effect) NMR experiments. Thus irradiation
of the <italic toggle="yes">tert</italic>-butyl resonance of <bold>5</bold> gave a strong enhancement of
the pyridyl group ortho-H (H<sup>6</sup>) resonance. This would only be
expected if the N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu group were positioned cis to this moiety.
The compound <bold>5</bold> is unstable in solution over 24 h, and we were
not able to obtain diffraction quality crystals. Addition of
pyridine to <bold>5</bold> reforms <bold>2</bold>, consistent with the former being a
possible intermediate in the dynamic NMR spectra of <bold>2</bold>. The
NMR spectra of <bold>5</bold> are fully consistent with the C<sub>s</sub> symmetric,
trigonal bipyramidal structure shown in eq 4.
<fig id="ic0102541f5" position="float" orientation="portrait"><label></label><graphic xlink:href="ic0102541f5.tif" position="float" orientation="portrait"></graphic></fig></p><p>To characterize fully the fluxional processes for [M(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (M = Nb <bold>2</bold> or Ta <bold>3</bold>) we have determined the
associated activation parameters from <sup>1</sup>H NMR line shape
analyses for <bold>3 </bold>(in the slow exchange limit) and coalesence
measurements (<bold>2</bold> and <bold>3</bold>) of the inequivalent SiMe<sub>3</sub> groups. The
closely overlapping nature of the relevant signals for the
arylimido analogue <bold>4</bold> prevented us from making a similar study
of this system. The results are summarized in Table <xref rid="ic0102541t00004"></xref>, and
Figure <xref rid="ic0102541f00004"></xref> shows an Eyring plot for SiMe<sub>3</sub> group exchange in <bold>3</bold>.
<fig id="ic0102541f00004" position="float" orientation="portrait"><label>4</label><caption><p>Eyring plot for for SiMe<sub>3</sub> group exchange in [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>3</bold>). Refer to the text and Table <xref rid="ic0102541t00004"></xref> for further details.</p></caption><graphic xlink:href="ic0102541f00004.tif" position="float" orientation="portrait"></graphic></fig><table-wrap id="ic0102541t00004" position="float" orientation="portrait"><label>4</label><caption><p>Rate Constants and Activation Parameters for SiMe<sub>3</sub> Group Exchange in [M(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>P</sub><sub>y</sub>)(py)] (M = Nb <bold>2</bold> or Ta <bold>3</bold>) (refer to the
text for further details)</p></caption><oasis:table colsep="2" rowsep="2"><oasis:tgroup cols="1"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry colname="1">(a) Results for <bold>3</bold> from <sup>1</sup>H NMR line shape analysis:</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup><oasis:tgroup cols="4"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:colspec colnum="3" colname="3"></oasis:colspec><oasis:colspec colnum="4" colname="4"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry namest="1" nameend="1">temperature (K)</oasis:entry><oasis:entry namest="2" nameend="2">avg corrected ν<sub>1/2</sub> (Hz)</oasis:entry><oasis:entry namest="3" nameend="3"><italic toggle="yes">k</italic><sub>obs</sub> (s<sup>-1</sup>)</oasis:entry><oasis:entry namest="4" nameend="4"><italic toggle="yes">k</italic><sub>exch </sub>(s<sup>-1</sup>)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">262
</oasis:entry><oasis:entry colname="2">0.48
</oasis:entry><oasis:entry colname="3">1.51
</oasis:entry><oasis:entry colname="4">3.02
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">267
</oasis:entry><oasis:entry colname="2">1.00
</oasis:entry><oasis:entry colname="3">3.14
</oasis:entry><oasis:entry colname="4">6.28
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">271
</oasis:entry><oasis:entry colname="2">2.08
</oasis:entry><oasis:entry colname="3">6.54
</oasis:entry><oasis:entry colname="4">13.1
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">275
</oasis:entry><oasis:entry colname="2">3.57
</oasis:entry><oasis:entry colname="3">11.2
</oasis:entry><oasis:entry colname="4">22.4
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">279
</oasis:entry><oasis:entry colname="2">6.30
</oasis:entry><oasis:entry colname="3">19.8
</oasis:entry><oasis:entry colname="4">39.6
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">283
</oasis:entry><oasis:entry colname="2">10.2
</oasis:entry><oasis:entry colname="3">32.0
</oasis:entry><oasis:entry colname="4">64.0
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">287
</oasis:entry><oasis:entry colname="2">17.0
</oasis:entry><oasis:entry colname="3">53.4
</oasis:entry><oasis:entry colname="4">107
</oasis:entry></oasis:row><oasis:row><oasis:entry namest="1" nameend="4">∴ Δ<italic toggle="yes">H</italic><sup>‡</sup> = 87.6 ± 2.3 kJ mol<sup>-1</sup>; Δ<italic toggle="yes">S</italic><sup>‡</sup> = 99 ± 10 J mol<sup>-1 </sup>K<sup>-1</sup></oasis:entry></oasis:row></oasis:tbody></oasis:tgroup><oasis:tgroup cols="1"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry colname="1">(b) Gibbs free energies of activation for <bold>2</bold> and <bold>3</bold> at 268 and 300 K:</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup><oasis:tgroup cols="2"><oasis:colspec colnum="1" colname="1"></oasis:colspec><oasis:colspec colnum="2" colname="2"></oasis:colspec><oasis:tbody><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2"></oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">For <bold>2</bold>:
</oasis:entry><oasis:entry colname="2">Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(268 K)</sub> = 53.7 ± 1.0 kJ.mol<sup>-1</sup> (from coalescence measurements)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1">For <bold>3</bold>:
</oasis:entry><oasis:entry colname="2">Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(268 K)</sub> = 61.1 ± 2.5 kJ mol<sup>-1</sup> (from Eyring plot Δ<italic toggle="yes">H</italic><sup>‡</sup> and Δ<italic toggle="yes">S</italic><sup>‡</sup> values)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2">Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(300 K)</sub> = 58.0 ± 2.5 kJ mol<sup>-1</sup> (from Eyring plot Δ<italic toggle="yes">H</italic><sup>‡</sup> and Δ<italic toggle="yes">S</italic><sup>‡</sup> values)
</oasis:entry></oasis:row><oasis:row><oasis:entry colname="1"></oasis:entry><oasis:entry colname="2">Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(300 K)</sub> = 61.1 ± 1.0 kJ mol<sup>-1</sup> (from coalescence measurements)</oasis:entry></oasis:row></oasis:tbody></oasis:tgroup></oasis:table></table-wrap></p><p>Activation parameters for SiMe<sub>3</sub> group exchange [Ta(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] (<bold>3</bold>) were obtained from <sup>1</sup>H NMR spectra of <bold>3</bold>
between 262 and 287 K in the slow exchange regime. Curve
fitting of the SiMe<sub>3</sub> resonances afforded ν<sub>1/2</sub> (bandwidth at half-height) values, from which were subtracted the natural line
widths as obtained at 218 K to give corrected ν<sub>1/2</sub> values. At
each temperature, the first-order <italic toggle="yes">k</italic><sub>obs</sub> value was calculated from
the average corrected ν<sub>1/2</sub> value (Table <xref rid="ic0102541t00004"></xref>) according to the expression <italic toggle="yes">k</italic><sub>obs</sub> = π·ν<sub>1/2</sub>. Taking chemical <italic toggle="yes">exchange</italic> rate constants
(<italic toggle="yes">k</italic><sub>exch</sub>) as 2·<italic toggle="yes">k</italic><sub>obs</sub><xref rid="ic0102541b00054" ref-type="bibr"></xref> we obtained the activation parameters listed
in Table <xref rid="ic0102541t00004"></xref> from the Eyring plot shown in Figure <xref rid="ic0102541f00004"></xref>. As a check
of the reliability of the Δ<italic toggle="yes">S</italic><sup>‡</sup> and Δ<italic toggle="yes">H</italic><sup>‡</sup> values obtained from the
line shape analysis, we extracted Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(300 K)</sub> (Table <xref rid="ic0102541t00004"></xref>) from <sup>1</sup>H
coalescence measurements for the SiMe<sub>3</sub> resonances (at 300 K)
using the standard procedures.<xref rid="ic0102541b00054" ref-type="bibr">54a</xref> The value of Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(300 K)</sub> from
coalescence measurements (61.1 ± 1.0 kJ mol<sup>-1</sup>) compares very
well with the value of Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(300 K)</sub> (58.0 ± 2.5 kJ.mol<sup>-1</sup>)
calculated from the Δ<italic toggle="yes">S</italic><sup>‡</sup> and Δ<italic toggle="yes">H</italic><sup>‡</sup> values from <sup>1</sup>H line shape
analysis. The sign and magnitude of these parameters are
consistent with the exchange mechanism shown in eq 4.<xref rid="ic0102541b00055" ref-type="bibr"></xref></p><p>Table <xref rid="ic0102541t00004"></xref> also gives the Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(268K)</sub> values for SiMe<sub>3</sub> group
exchange for the niobium congener <bold>2</bold>; the corresponding value
for <bold>3</bold> was calculated from the Δ<italic toggle="yes">H</italic><sup>‡</sup> and Δ<italic toggle="yes">S</italic><sup>‡</sup> data for comparison.
The data clearly show that the activation free energy for [M(N<italic toggle="yes"><sup>t</sup></italic><sup></sup>Bu)Cl(N<sub>2</sub>N<sub>py</sub>)(py)] with M = Ta (<bold>3</bold>, 61.1 ± 2.5 kJ mol<sup>-1</sup>) is
higher than that for Nb (<bold>2</bold>, 53.7 ± 1.0 kJ mol<sup>-1</sup>). Assuming
that the activation entropy <italic toggle="yes">Δ</italic><italic toggle="yes">S</italic><sup>‡</sup> is more or less the same for the
exchange processes in <bold>2</bold> and <bold>3</bold>, the differences in Δ<italic toggle="yes">G</italic><sup>‡</sup><sub>(268K)</sub>
values reflect differences in enthalpies of activation, Δ<italic toggle="yes">H</italic><sup>‡</sup>. The
increase in Δ<italic toggle="yes">H</italic><sup>‡</sup> from M = Nb to Ta is consistent with the well-known increase in metal−ligand bond strengths down a transition metal triad.<xref rid="ic0102541b00056" ref-type="bibr"></xref></p></sec><sec id="d7e5670"><title>Conclusions</title><p>The diamido-pyridine ligands employed in this study provided
the key to developing a new class of Group 5 imido complexes.
While the synthesis of vanadium complexes was hampered by
ligand degradation and redox side-reactions, a series of niobium
and tantalum imido complexes was prepared and structurally
characterized; the solution dynamics of the new complexes were
fully analyzed, and one potential intermediate in these processes
was isolated. Future studies on these systems will concentrate
on the reaction chemistry supported by the new diamido-pyridine-imide ligand sets.
</p></sec></body><back><ack><title>Acknowledgments</title><p>We thank Dr. P. A. Cooke for help with
the X-ray data collection. We also thank the Deutsche Forschungsgemeinschaft, the Engineering and Physical Sciences
Research Council, the Leverhulme Trust, the Fonds der Chemischen Industrie, the Royal Society, the DAAD, and the British
Council for financial support.
</p></ack><notes notes-type="si"><sec id="d7e5682"><title><ext-link xlink:href="/doi/suppl/10.1021%2Fic0102541">Supporting Information Available</ext-link></title><p>X-ray crystallographic files
in CIF format for the structure determinations of <bold>1</bold>, <bold>2</bold>, <bold>3</bold>, and <bold>4</bold>. This
material is available free of charge via the Internet at <uri xlink:href="http://pubs.acs.org">http://pubs.acs.org</uri>.
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Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal" displayLabel="corresp"><namePart type="family">MOUNTFORD</namePart><namePart type="given">Philip</namePart><affiliation>Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K.,School of Chemistry, University of Nottingham, Nottingham, NG7 2RD, U.K.,and Laboratoire de Chimie Organométallique et de Catalyse (CNRS UMR 7513), Institut Le Bel,Université Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France</affiliation><affiliation> University of Oxford.</affiliation><affiliation> To whom correspondence should be addressed. Lutz H. Gade e-mail: gade@chimie.u-strasbg.fr. Philip Mountford e-mail: philip.mountford@chemistry.oxford.ac.uk. Fax: +44 1865 272690</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article" authority="ISTEX" authorityURI="https://content-type.data.istex.fr" valueURI="https://content-type.data.istex.fr/ark:/67375/XTP-1JC4F85T-7">research-article</genre><originInfo><publisher>American Chemical Society</publisher><dateCreated encoding="w3cdtf">2001-06-30</dateCreated><dateIssued encoding="w3cdtf">2001-07-30</dateIssued><copyrightDate encoding="w3cdtf">2001</copyrightDate></originInfo><abstract>Reaction of the vanadium(V) imide [V(NAr)Cl3(THF)] (Ar = 2,6-C6H3iPr2) with the diamino-pyridine derivative MeC(2-C5H4N)(CH2NHSiMe2tBu)2 (abbreviated as H2N‘2Npy) gave modest yields of the vanadium(IV) species [V(NAr)(H3N‘N‘ ‘Npy)Cl2] (1 where H3N‘N‘ ‘Npy = MeC(2- C5H4N)(CH2NH2)(CH2NHSiMe2tBu) in which the original H2N‘2Npy has effectively lost SiMe2tBu (as ClSiMe2tBu) and gained an H atom. Better behaved reactions were found between the heavier Group 5 metal complexes [M(NR)Cl3(py)2] (M = Nb or Ta, R = tBu or Ar) and the dilithium salt Li2[N2Npy] (where H2N2Npy = MeC(2-C5H4N)(CH2NHSiMe3)2), and these yielded the six-coordinate M(V) complexes [M(NR)Cl(N2Npy)(py)] (M = Nb, R = tBu 2; M = Ta, R = tBu 3 or Ar 4). The compounds 2−4 are fluxional in solution and undergo dynamic exchange processes via the corresponding five-coordinate homologues [M(NR)Cl(N2Npy)]. Activation parameters are reported for the complexes 2 and 3. In the case of 2, high vacuum tube sublimation afforded modest quantities of [Nb(NtBu)Cl(N2Npy)] (5). The X-ray crystal structures of the four compounds 1, 2, 3, and 4 are reported.</abstract><abstract type="short">New Group 5 imido complexes derived from the diamido-pyridine ligand MeC(2-C5H4N)(CH2CH2NSiMe3)2 (N2Npy) are described. Among those reported are products of the reactions of Li2[N2Npy] with [M(NR)Cl3(py)2] (M = Nb, Ta; R = tBu, Ar) which gave compounds of the type shown. The X-ray structures and solution dynamics of the new compounds are described.</abstract><relatedItem type="host"><titleInfo><title>Inorganic Chemistry</title></titleInfo><titleInfo type="abbreviated"><title>Inorg. Chem.</title></titleInfo><genre type="journal" authority="ISTEX" authorityURI="https://publication-type.data.istex.fr" valueURI="https://publication-type.data.istex.fr/ark:/67375/JMC-0GLKJH51-B">journal</genre><identifier type="ISSN">0020-1669</identifier><identifier type="eISSN">1520-510X</identifier><identifier type="acspubs">ic</identifier><identifier type="coden">INOCAJ</identifier><identifier type="uri">pubs.acs.org/IC</identifier><part><date>2001</date><detail type="volume"><caption>vol.</caption><number>40</number></detail><detail type="issue"><caption>no.</caption><number>16</number></detail><extent unit="pages"><start>3992</start><end>4001</end></extent></part></relatedItem><identifier type="istex">D6A7FC5D2E9DFB03A59535075204206D6A350B5F</identifier><identifier type="ark">ark:/67375/TPS-BHD9X61C-B</identifier><identifier type="DOI">10.1021/ic0102541</identifier><accessCondition type="use and reproduction" contentType="restricted">Copyright © 2001 American Chemical Society</accessCondition><recordInfo><recordContentSource authority="ISTEX" authorityURI="https://loaded-corpus.data.istex.fr" valueURI="https://loaded-corpus.data.istex.fr/ark:/67375/XBH-X5HBJWF8-J">ACS</recordContentSource><recordOrigin>Copyright © 2001 American Chemical Society</recordOrigin></recordInfo></mods><json:item><extension>json</extension><original>false</original><mimetype>application/json</mimetype><uri>https://api.istex.fr/ark:/67375/TPS-BHD9X61C-B/record.json</uri></json:item></metadata><annexes><json:item><extension>tiff</extension><original>true</original><mimetype>image/tiff</mimetype><uri>https://api.istex.fr/document/D6A7FC5D2E9DFB03A59535075204206D6A350B5F/annexes/tiff</uri></json:item></annexes><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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