Cationic Methyl- and Chlorotitanium Phosphinimide Complexes

A variety of donor-stabilized cationic complexes of the form [Cp(NPt-Bu3)TiMe(L)][MeB(C6F5)3] and [Cp(NPt-Bu3)TiMe(L)][B(C6F5)4] (L = Py, 4-EtPy, 4-t-BuPy, NC5H4NMe2, PMe3, Pn-Bu3, PPh3, P(p-MeC6H4)3)have been prepared and characterized. Prolonged storage in CH2Cl2 solution resulted in chloride for methyl exchange to afford species of the form [CpTi(NPt-Bu3)Cl(L)][B(C6F5)4], [{CpTi(NPt-Bu3)Me}2(μ-Cl)][B(C6F5)4], and [CpTi(NPt-Bu3)(μ-Cl)]2[MeB(C6F5)3]2. The byproduct salt [(o-MeC6H4)3PCH2Cl][B(C6F5)4] was obtained from reactions employing the sterically demanding donor phosphine P(o-MeC6H4)3, suggesting transient generation of the cation [CpTi(NPt-Bu3)Cl(CH2Cl2)]+. Analogous reactivity was not seen in C6H5Cl, although the species [{CpTi(NPt-Bu3)Me}2(μ-Me)][B(C6F5)4] could be formed in this solvent. The isolated zwitterionic complex TiCp(NPt-Bu3)Me(μ-MeB(C6F5)3) readily performs insertion chemistry into the Ti−methyl bonds with diisopropylcarbodiimide and diphenylacetylene substrates to afford the cationic species [CpTi(NPt-Bu3)((Ni-Pr)2CMe)][MeB(C6F5)3], [TiCp(NPt-Bu3)(PhCCPh(Me))][MeB(C6F5)3], and [TiCp(NPt-Bu3)(PhCCPh(Me))(PMe3)][MeB(C6F5)3]. The implications of this chemistry are considered.