Efficient catalytic reduction of ketones with formic acid and ruthenium complexes

The ruthenium complex (eta(5)-C(4)Ph(4)COHOC(4)Ph(4)-eta(5))(mu-H)(CO)(4)Ru-2 and its phenyl ring-substituted derivatives were found to act as efficient catalysts in reduction reactions of aldehydes and ketones to alcohols, using formic acid as H source. Excess formic acid accelerates the reaction, and the corresponding formate esters were isolated as sole products. Turnover numbers of up to 8000 (alcohols) and 11000 (formate esters) were attained, with yields in the order of 90%. Alkenes are not reactive, however, double bonds conjugated to a carbonyl group are selectively reduced under the reaction conditions, The reaction is compatible with a variety of ketones, but with aliphatic aldehydes the reaction is not selective, inasmuch as aldol condensation products are formed.