Ruthenium xantphos complexes in hydrogen transfer processes: reactivity and mechanistic studies

The in situ combination of [Ru(PPh3)(3)(CO)H-2] with xantphos is catalytically active for the alkylation of alcohols with the ketonitrile (BuC)-Bu-t(O)CH2CN in a model oxidation-Knoevenagel-reduction process. The precursor complex [Ru(xantphos)(PPh3)(CO)H-2] was isolated and reacted with stoichiometric amounts of PhCH2OH and PhCHO. Under these conditions, the alcohol is decarbonylated to afford [Ru(xantphos)(CO)(2)H-2] and finally [Ru(xantphos)(CO)(3)], both of which prove to be less active for catalysis than the starting complex. The reactivity of the xantphos system contrasts with that of [Ru(dppp)(PPh3)(CO)H-2], which is catalytically inactive for the Knoevenagel reaction and fails to show any stoichiometric reactivity with alcohols.