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 PPh 3 -substituted hydroxycyclopentadienyl ruthenium hydride [2,5-Ph 2 -3,4-Tol 2 (η 5 -C 4 COH)]Ru(CO)(PPh 3 )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 1 at elevated temperatures and pressures. 1 shows high chemoselectivity for catalytic hydrogenation of aldehydes over ketones, while 2 is much less selective.