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New Titanium Complexes Containing an Amidinate−Imide Supporting Ligand Set:  Cyclopentadienyl, Alkyl, Borohydride, Aryloxide, and Amide Derivatives

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journal contribution
posted on 02.07.1998, 00:00 by Peter J. Stewart, Alexander J. Blake, Philip Mountford
A range of chloride metathesis reactions of the monomeric titanium N,N‘-bis(trimethylsilyl)benzamidinato−imido complexes [Ti(NBut){(4-C6H4R)C(NSiMe3)2}Cl(py)2] (R = H (1) or OMe (2)) are described. Thus, reaction of 1 or 2 with LiC5H5 gave the half-sandwich compounds [Ti(NBut){(4-C6H4R)C(NSiMe3)2}(η-C5H5)] (R = H (3) or OMe (4)). Reaction of 1 with LiCH2SiMe3 or LiCH(SiMe3)2 gave the 14-electron, first fully characterized group 4 imido−alkyl derivatives [Ti(NBut){PhC(NSiMe3)2}{CH(R)SiMe3}(py)] (R = H (5) or SiMe3 (6)). For comparative purposes, the 16-electron half-sandwich imido−alkyl complex [Ti(NBut)(ηC5Me5)(CH2SiMe3)(py)] (7) was prepared from LiCH2SiMe3 and [Ti(NBut)(η-C5Me5)Cl(py)]. Reaction of 1 with LiBH4 gave the η3-borohydride derivative [Ti(NBut){PhC(NSiMe3)2}(η3-BH4)(py)] (8), while treatment of 1 with LiN(SiMe3)2, LiO-2,6-C6H3R2 (R = Me or But), or LiPhC(NSiMe3)2 gave the corresponding aryloxide, amide, or bis(benzamidinate) titanium imido complexes [Ti(NBut){PhC(NSiMe3)2}{N(SiMe3)2}(py)] (9), [Ti(NBut){PhC(NSiMe3)2}(O-2,6-C6H3R2)(py)] (R = Me (10) or But (11)), or [Ti(NBut){PhC(NSiMe3)2}2(py)] (13). Activation parameters for the concerted, restricted rotation of the aryloxide and benzamidinate ligands in 11 are reported and point to a dissociatively activated mechanism. The X-ray structures of 5 and 7 have been determined.