The PPh₃-Substituted Hydroxycyclopentadienyl Ruthenium Hydride [2,5-Ph₂-3,4-Tol₂(η⁵-C₄COH)]Ru(CO)(PPh₃)H Is a More Efficient Catalyst for Hydrogenation of Aldehydes

The phosphine-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)(PPh3)H (8) displayed behavior significantly different from that of the dicarbonyl analogue, including the failure to form an unreactive diruthenium complex analogous to the Shvo catalyst 5. Complex 8 shows no apparent reduction of aldehydes in the absence of a trap but exchanges deuterium between the hydride of 8-RuDOD and the aldehydic hydrogen of p-tolualdehyde. This provides evidence that aldehyde reduction by 8 occurs but is reversible. 8 catalyzes the hydrogenation of benzaldehyde under mild temperature and pressure conditions. A rate law of −d[RCHO]/dt = k[RCHO][8][H2]0 was obtained.