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

A range of chloride metathesis reactions of the monomeric titanium N,N‘-bis(trimethylsilyl)benzamidinato−imido complexes [Ti(NBu^t){(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(NBu^t){(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(NBu^t){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(NBu^t)(ηC₅Me₅)(CH₂SiMe₃)(py)] (7) was prepared from LiCH₂SiMe₃ and [Ti(NBu^t)(η-C₅Me₅)Cl(py)]. Reaction of 1 with LiBH₄ gave the η³-borohydride derivative [Ti(NBu^t){PhC(NSiMe₃)₂}(η³-BH₄)(py)] (8), while treatment of 1 with LiN(SiMe₃)₂, LiO-2,6-C₆H₃R₂ (R = Me or Bu^t), or LiPhC(NSiMe₃)₂ gave the corresponding aryloxide, amide, or bis(benzamidinate) titanium imido complexes [Ti(NBu^t){PhC(NSiMe₃)₂}{N(SiMe₃)₂}(py)] (9), [Ti(NBu^t){PhC(NSiMe₃)₂}(O-2,6-C₆H₃R₂)(py)] (R = Me (10) or Bu^t (11)), or [Ti(NBu^t){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.