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 ' N=CHtol (Ar ' = 2,6-Me2C6H3, tol = 4-MeC6H4), and depending on the reaction conditions, results in isolation of [Me2N=CHR '][B(C6F5)(4)] (1) or (Me2N)(2)CHtol, as well as the asymmetric titanium dimer [(Me2N)(2)(HNMe2)Ti(mu(2)-N[2,6-Me2C6H3])(2)Ti(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-(Pr2C6H3)-Pr-i] results in formation of the imido salts [CpTi(=N[2,6-(Pr2C6H3)-Pr-i])(NHMe2)(2)][B(C6F5)(4)] (5) (58% yield) or [Cp*Ti(=N[2,6-(Pr2C6H3)-Pr-i])(NHMe2)(2)][B(C6F5)(4)] (6). When Ti(NMe2)(4) is treated with [Et3Si][B(C6F5)(4)], the salt [Ti(NMe2)(3)(N[SiEt3]Me-2)][B(C6F5)(4)] (7) is obtained, and treatment of the latter with [2,6-(Pr2C6H3)-Pr-i]N = CHtol produces the imine adduct [Ti(NMe2)(3)(kappa(1)-[2,6-(Pr2C6H3)-Pr-i]N=CHtol)][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. (C) 2010 Elsevier B.V. All rights reserved.