Functional phosphines XII. Heterolytic H2 cleavage and homogeneous 2 bonds on the lefthand side signC=O hydrogenation catalyzed by platinum metal β-aminophosphine complexes

Article abstract of DOI:10.1016/S1387-7003(03)00009-1

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.