Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of CC and CO bonds

Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)2(OAc)2(PnBu3)[P(p-XC6H4)3] (OAc = acetate, X = CH3O, CH3, H, F or Cl), containing different phosphine ligands trans to PnBu3, have been employed as catalyst precursors for the hydrogenation of 1-hexene, acetophenone, 2-butanone and benzylideneacetone. For comparative purposes, analogous reactions have been performed using the homodiphosphine precursors Ru(CO)2(OAc)2(PnBu3)2 and Ru(CO)2(OAc)2(PPh3)2. The catalytic activity of the heterodiphosphine complexes depends on the basicity of the triarylphosphine trans to PnBu3 as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)2(H)(OAc)(PnBu3)[P(p-XC6H4)3], or dihydride, Ru(CO)2(H)2(PnBu3)[(p-XC6H4)3], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the CC double bond is best accomplished by homodiphosphine dihydride catalysts, while heterodiphosphine monohydrides are more efficient catalysts than the homo- and heterodiphosphine dihydrides for the reduction of the keto CO bond.

Bis(acetate) ruthenium(II) complexes Ru(CO)2(OAc)2(PnBu3)[P(p-XC6H4)3], containing different phosphine ligands trans to PnBu3, have been employed as catalyst precursors for the hydrogenation of alkenes, ketones and α,β-unsaturated ketones.The heterodiphosphine monohydride catalysts show an excellent selectivity in the hydrogenation of trans-4-phenyl-3-buten-2-one to the corresponding allylic alcohol, trans-4-phenyl-3-buten-2-ol (>90%).Figure optionsDownload as PowerPoint slide