Coordination of a Bifunctional Ligand to a Rhodium(III) Dimethyl Complex: Lewis Acidity Enhancement by Chelation

Abstract

The addition of the ambiphilic compound (Me2PCH2AlMe2)2 (1) to Cp*RhMe2(DMSO) (DMSO = dimethylsulfoxide) (2) gives Cp*RhMe2(PMe2CH2AlMe2·DMSO) (3·DMSO). The addition of Lewis acids (LA) such as La(dbm)3 (dbm = dibenzoylmethane) and AlMe3 to a solution of complex 3·DMSO gives a competition reaction that results in the formation of LA·DMSO and Cp*RhMe2(PMe2CH2AlMe2) (3). When heated to 40 °C, complex 3 ionizes to a putative zwitterionic species, Cp*Rh+Me(PMe2CH2AlMe3-) (3‘), which is converted to [Cp*Rh(Me)(μ2-η2-Me2PCH2)]2 (4) irreversibly. Spin saturation transfer experiments demonstrated that the rate of the methyl abstraction by the alane moiety was 0.76 ± 0.09 s-1, while the rate of abstraction of the methyl in Cp*RhMe2(PMe3) by AlMe3 was 0.10 ± 0.02 s-1. The zwitterionic species 3‘ could be trapped in solution by addition of PMe3 to afford both Cp*Rh+Me(PMe3)(Me2PCH2AlMe3-) (5) and [Cp*Rh+Me(PMe3)(Me2PCH2AlMe2)]AlMe4- (6). When compound 1 was added to complex 3‘, the formation of the zwitterionic comp...