Mononuclear ruthenium complexes containing two different phosphines in trans position: II. Catalytic hydrogenation of C=C and C=O bonds

Bis(acetate) ruthenium(II) complexes of the general formula Ru(CO)(2)(OAc)(2)((PBu3)-Bu-n)[P(P-XC6H4)(3)] (OAc = acetate, X = CH3O, CH3, H, F or Cl), containing different phosphine ligands trans to (PBu3)-Bu-n, 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)((PBu3)-Bu-n)(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 (PBu3)-Bu-n as this factor controls, inter alia, the rate of formation of hydride(acetate), Ru(CO)(2)(H)(OAc)((PBu3)-Bu-n)[P(p-XC6H4)(3)], or dihydride, Ru(CO)(2)(H)2((PBu3)-Bu-n)[(p-XC6H4)(3)], complexes, by hydrogenation of the bis(OAc) precursors. The catalytic hydrogenation of the C=C 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 C=O bond. (c) 2006 Elsevier B.V. All rights reserved.