Nucleophilic Attack toward Group 4 Metal Complexes Bearing Reactive 1-Aza-1,3-butadienyl and Imido Moieties

Unique (1-aza-2-butenyl)titanium complexes bearing a phosphonium ylide moiety [TiNTbt{C(Me)(PR3)CHC(Me)N(Mes)}Cl] (3−5, Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes = 2,4,6-trimethylphenyl) were formed by the
nucleophilic attack of PMe3, P(n-Bu)3, and 1,2-bis(dimethylphosphino)ethane (dmpe) toward the corresponding (1-aza-1,3-butadienyl)titanium complex, [TiNTbt{C(Me)CHC(Me)N(Mes)}(μ-Cl)2Li(tmeda)] (2a). The reaction of a
lithium β-diketiminate, [Li{N(Tbt)C(Me)CHC(Me)N(Mes)}] (1) with [TiIICl2(dmpe)2] also resulted in the formation of
the same complex 5. Density functional theory calculation indicated that the negative charge of the model molecule
of 3 was slightly delocalized to the C3N plane. In addition, the calculation of the model molecule of 2a suggested
the electrophilicity of 2a at the carbon atom connecting to the titanium atom. Interestingly, the reaction of zirconium
and hafnium analogues (2b and 2c) with PMe3 and dmpe did not proceed. In contrast to the cases of phosphine
reagents, pyridine which was found to undergo the nucleophilic attack toward the titanium center of 2a gave the
pyridine-coordinated titanium-imide [TiNTbt{C(Me)CHC(Me)N(Mes)}Cl(py)] (7).