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Synthesis of a Base-Free Titanium Imido and a Transient Alkylidene from a Titanocene Dinitrogen Complex. Studies on TiNR Hydrogenation, Nitrene Group Transfer, and Comparison of 1,2-Addition Rates

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Tamara E. Hanna, Ivan Keresztes, Emil Lobkovsky, Wesley H. Bernskoetter, and Paul J. Chirik*

Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853

Organometallics, 2004, 23 (14), pp 3448–3458

DOI: 10.1021/om049817h

Publication Date (Web): June 8, 2004

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Abstract

The synthesis and reactivity of the end-on bound dinitrogen complex [(η⁵-C₅H₃-1,3-(SiMe₃)₂)₂Ti]₂(μ₂,η¹,η¹-N₂) is described. The solid state structure of the dinitrogen compound reveals a weakly activated end-on bound N₂ ligand with an N−N bond length of 1.164(5) Å. Displacement of the N₂ ligand by organic azides has been used to prepare monomeric, base-free titanocene imido complexes, (η⁵-C₅H₃-1,3-(SiMe₃)₂)₂TiNR (R = SiMe₃, 2,4,6-Me₃-C₆H₂). While unreactive toward C−H bonds, the Ti−N linkage is readily hydrogenated and participates in group transfer reactions with unsaturated organic molecules such as carbon monoxide and benzophenone. Reaction of the N₂ complex with Ph₂CN₂ allowed isolation of (η⁵-C₅H₃-1,3-(SiMe₃)₂)₂Ti(N₂CPh₂), which exists as a mixture of interconverting η² and η¹ isomers in solution. The diazoalkane complex also participates in “imido-like” reactivity, producing (η⁵-C₅H₃-1,3-(SiMe₃)₂)₂Ti(NHNCPh₂)H upon addition of H₂. Changing the diazoalkane to Me₃SiCHN₂ resulted in isolation of the double cyclometalated titanocene (η⁵-C₅H₃-η¹-1-SiMe₂CH₂-3-SiMe₃)₂Ti, arising from facile intramolecular C−H activation of the cyclopentadienyl substituent by a transient titanocene alkylidene.

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Published In Issue July 05, 2004
Received March 12, 2004

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Article

Synthesis of a Base-Free Titanium Imido and a Transient Alkylidene from a Titanocene Dinitrogen Complex. Studies on TiNR Hydrogenation, Nitrene Group Transfer, and Comparison of 1,2-Addition Rates