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

Abstract

The in situ combination of [Ru(PPh₃)₃(CO)H₂] with xantphos is catalytically active for the alkylation of alcohols with the ketonitrile^tBuC(O)CH₂CN in a model oxidation–Knoevenagel–reduction process. The precursor complex [Ru(xantphos)(PPh₃)(CO)H₂] was isolated and reacted with stoichiometric amounts of PhCH₂OH and PhCHO. Under these conditions, the alcohol is decarbonylated to afford [Ru(xantphos)(CO)₂H₂] 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)H₂], which is catalytically inactive for the Knoevenagel reaction and fails to show any stoichiometric reactivity with alcohols.