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-Ph 2 -3,4-Tol 2 (η 5 -C 4 COH)]Ru(CO)(PPh 3 )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]/d t = k [RCH O][ 8 ][H 2 ] 0 was obtained.