Functional phosphines XII. Heterolytic H2 cleavage and homogeneous CO hydrogenation catalyzed by platinum metal β-aminophosphine complexes

Acetophenone was enantioselectively reduced to 1-phenylethanol (21–71% e.e.) by the use of base-modified Ir and Rh catalysts derived from optically active β-aminophosphines, [{(1R,2S)-, (1R,2R)-, (1S,2S)-Ph2PCH(Ph)CH(Me)N(H)R}M(COD)]BF4–KOH (R=H, Me, i-Pr, CH2Ph), in methanol under H2 (10 bar). The isolation of an equally active amidoiridium catalyst, [(Ph2PCH2CMe2NH)Ir(COD)], its ability to oxidatively add dihydrogen, and the observation of both H2/D+ and H2/D2 exchange reactions during catalysis, which crucially depends on the use of protic solvents, provided evidence for a mechanism involving hydride and proton transfer as well as heterolytic H2 cleavage on dihydrogen–hydrido–amido and dihydrido–amine tautomers, [{‘P∩NR’}Ir(H2)H]+ and [{‘P∩N(H)R’}IrH2]+, respectively.