ORGANOMETALLIC CATALYSIS IN AQUEOUS-SOLUTIONS - THE BIPHASIC TRANSFER HYDROGENATION OF ALDEHYDES CATALYZED BY WATER-SOLUBLE PHOSPHINE COMPLEXES OF RUTHENIUM, RHODIUM AND IRIDIUM

Aromatic and aliphatic aldehydes can be reduced to the corresponding alcohols by hydrogen transfer from formate using, as catalysts, water-soluble complexes of Ru(II), Rh(I) and Ir(I) with monosulphonated triphenylphosphine (mSPφ)2, in aqueous/organic biphasic systems without phase transfer catalysts. HRu(O2CH)(mSPφ)2)3 was identified as the key intermediate in the processes catalyzed by RuCl2(mSPφ2)2 in an excess of phosphine. Olefinic double bonds (including those in α,β-unsaturated aldehydes), as well as substitutents of the aromatic ring, are not affected. Attempted catalysis of the transfer of benzaldehyde from the organic to the aqueous phase by β-cyclodextrin resulted in inhibition of the metal complex-catalyzed transfer hydrogenation. © 1990.