Molecular Dihydrogen Activation by (CMe)M/N (M=Rh, Ir) Transition Metal Frustrated Lewis Pairs: Reversible Proton Migration to, and Proton Abstraction from, the CMe Ligand.

The masked transition-metal frustrated Lewis pairs [Cp*M(κN,N',N''-L)][SbF] (Cp*=η-CMe; M=Ir, 1, Rh, 2; HL=pyridinyl-amidine ligand) reversibly activate H under mild conditions rendering the hydrido derivatives [Cp*MH(κN,N'-HL)][SbF] observed as a mixture of the E and Z isomers at the amidine C=N bond (M=Ir, 3Z, 3E; M=Rh, 4Z, 4E). DFT calculations indicate that the formation of the E isomers follows a Grotthuss type mechanism in the presence of water. A mixture of Rh(I) isomers of formula [(Cp*H)Rh(κN,N'-HL)][SbF] (5 a-d) is obtained by reductive elimination of Cp*H from 4.