The use of several tertiary-phosphine–ruthenium complexes in the catalytic hydroformylation of alkenes is described. For mononuclear complexes the conversions into aldehyde, as well as the ratios of straight- to branched-chain aldehyde are essentially constant; the ruthenium complex recovered from the reactions is invariably tricarbonylbis(triphenylphosphine) ruthenium(0), Ru(CO)₃(PPh₃)₂. The dependence of conversion and aldehyde ratios on catalyst concentration, temperature, partial and total pressures, nature of the substrate, and addition of excess of triphenylphosphine and other ligands in hydroformylation with Ru(CO)₃(PPh₃)₂ is also described. Based on these results, a mechanism involving Ru(H)₂(CO)₂(PPh₃) as the principal active catalytic species is suggested.

The compound Ru(CO)₃(PPh₃)₂ is also active for the hydrogenation of alkenes and aldehydes and mechanisms for these reactions are suggested.

Complexes formed by addition of various ligands to dodecacarbonyltriruthenium, Ru₃(CO)₁₂, are shown to be less active for hydroformylation than mononuclear complexes.