The mechanism of hydrogenation of activated olefins, including prochiral ones, using trans-chlorohydridobis(diop)ruthenium(II)

Abstract

Solutions of the title complex trans-HRuCl(diop)₂, where diop is an optically active chelating ditertiary, hydrogenate under mild conditions activated olefinic substrates, including prochiral ones in high optical yields. Kinetic and spectroscopic studies on hydrogenation of acrylamide and β-phenylacrylic acid indicate an 'unsaturate' mechanism involving rapid coordination of the substrate to give an alkyl intermediate, that subsequently reacts with H₂ in a rate-determining step to yield the saturated product and the starting monohydride complex. A diop ligand dissociates to provide necessary coordination sites at the metal. The α-phenylacrylic acid coordinates more strongly than acrylamide, but hydrogenates more slowly.