PPh3-substituted [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)(PPh3)H exhibits slower stoichiometric reduction, faster catalytic hydrogenation, and higher chemoselectivity for hydrogenation of aldehydes over ketones than the dicarbonyl Shvo catalyst

The PPh3-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-Ph-2-3,4-Tol(2)(eta(5)-C4COH]Ru(CO)(PPh3)H (1) stoichiometrically reduces aldehydes and ketones in the presence of a pyridine trap to produce alcohols and the ruthenium pyridine complex 5, with a rate law that is dependent only on [aldehyde] and [1]. The observation of deuterium kinetic isotope effects on substitution of the acidic and hydridic protons of 1 are consistent with concerted transfer of hydrogen to aldehydes during reduction. 1 catalytically hydrogenates aldehydes under mild temperature and pressure conditions. While the Shvo catalyst 2 shows little activity under these conditions, it surpasses I at elevated temperatures and pressures. 1 shows high chemoselectivity for catalytic hydrogenation of aldehydes over ketones, while 2 is much less selective.