Molecular Dihydrogen Activation by (C 5 Me 5 )M/N (M=Rh, Ir) Transition Metal Frustrated Lewis Pairs: Reversible Proton Migration to, and Proton Abstraction from, the C 5 Me 5 Ligand.

The masked transition-metal frustrated Lewis pairs [Cp*M(κ 3 N,N',N''-L)][SbF 6 ] (Cp*=η 5 -C 5 Me 5 ; M=Ir, 1, Rh, 2; HL=pyridinyl-amidine ligand) reversibly activate H 2 under mild conditions rendering the hydrido derivatives [Cp*MH(κ 2 N,N'-HL)][SbF 6 ] 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(κ 2 N,N'-HL)][SbF 6 ] (5 a-d) is obtained by reductive elimination of Cp*H from 4. The formation of 5 a-d was elucidated by means of DFT calculations. Finally, when 2 reacts with D 2 , the Cp* and Cp*H ligands of the resulting rhodium complexes 4 and 5, respectively, are deuterated as a result of a reversible hydrogen abstraction from the Cp* ligand and D 2 activation at rhodium.