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-trisbis(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)}(mu-Cl)2Li(tmeda)] (2a). The reaction of a lithium beta-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).