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Cyclohexadienyl niobium complexes and arene hydrogenation catalysis

TitleCyclohexadienyl niobium complexes and arene hydrogenation catalysis
Publication TypeJournal Article
Year of Publication2002
AuthorsFryzuk, MD, Kozak, CM, Bowdridge, MR, Patrick, BO
JournalOrganometallics
Volume21
Pagination5047-5054
Date PublishedNov
Type of ArticleArticle
ISBN Number0276-7333
KeywordsAROMATIC-HYDROCARBONS, BOND, CHEMISTRY, CRYSTAL-STRUCTURE, HOMOGENEOUS HYDROGENATION, LIGANDS, TANTALUM DIHYDRIDE
Abstract

Hydrogenolysis of (R)[P2N2]NbCH2SiMe3 (where (R)[P2N2] = RP(CH2SiMe2NSiMe2CH2)(2)PR; R = cyclohexyl, Cy, or phenyl, Ph) in benzene or toluene causes hydride addition to the aromatic solvent resulting in the formation of the pi-bonded complexes (R)[P2N2]Nb(eta(5)-C6H7) (R = Cy, 1; R = Ph, 2) and (R)[P2N2]Nb(eta(5)-C7H9) (R = Cy, 3; R = Ph, 4) in benzene and toluene, respectively. Performing the hydrogenation at a higher pressure of 29 atm at room temperature causes the catalytic hydrogenation of benzene to cyclohexane as determined by NMR spectroscopy and GC-MS analysis. The hydrogenation of toluene to methylcyclohexane can also be performed, but the turnover frequency is considerably lower. Examination of the solid residues from the high-pressure hydrogenations indicates the formation of the pi-bonded complexes 1 and 2. The additionof 29 atm of H-2 to these cyclohexadienyl derivatives in benzene or toluene, however, shows no hydrogenation products, indicating these species are not catalytically active.

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