Understanding the role of an easy-to-prepare aldimine–alkyne carboamination catalyst, [Ti(NMe2)3(NHMe2)][B(C6F5)4]

A series of reactivity studies of the carboamination pre-catalyst [Ti(NMe2)3(NHMe2)][B(C6F5)4] as well as the preparation of other catalysts are reported in this work. Treatment of [Ti(NMe2)3(NHMe2)][B(C6F5)4] with the aldimines Ar′Ndouble bond; length as m-dashCHtol (Ar′ = 2,6-Me2C6H3, tol = 4-MeC6H4), and depending on the reaction conditions, results in isolation of [Me2Ndouble bond; length as m-dashCHR′][B(C6F5)4] (1) or (Me2N)2CHtol, as well as the asymmetric titanium dimer [(Me2N)2(HNMe2)Ti(μ2-N[2,6-Me2C6H3])2Ti(NHMe2)(NMe2)][B(C6F5)4] (2). Protonation of CpTi(NMe2)3 and Cp∗Ti(NMe2)3 results in isolation of the salts, [CpTi(NMe2)2(NHMe2)][B(C6F5)4] (3) and [Cp∗Ti(NMe2)2(NHMe2)][B(C6F5)4] (4), respectively. Treatment of compounds 3 or 4 with H2N[2,6-iPr2C6H3] results in formation of the imido salts [CpTi(double bond; length as m-dashN[2,6-iPr2C6H3])(NHMe2)2][B(C6F5)4] (5) (58% yield) or [Cp∗Ti(double bond; length as m-dashN[2,6-iPr2C6H3])(NHMe2)2][B(C6F5)4] (6). When Ti(NMe2)4 is treated with [Et3Si][B(C6F5)4], the salt [Ti(NMe2)3(N[SiEt3]Me2)][B(C6F5)4] (7) is obtained, and treatment of the latter with [2,6-iPr2C6H3]Ndouble bond; length as m-dashCHtol produces the imine adduct [Ti(NMe2)3(κ1-[2,6-iPr2C6H3]Ndouble bond; length as m-dashCHtol)][B(C6F5)4] (8). The carboamination catalytic activity of complexes 2–7 was investigated and compared to [Ti(NMe2)3(NHMe2)][B(C6F5)4]. Likewise, a proposed mechanism to the active carboamination catalyst stemming from [Ti(NMe2)3(NHMe2)][B(C6F5)4] is described.