Chemoselective hydrogenation of alpha-beta-insaturated ketones to allylic alcohols, catalyzed by a mononuclearruthenium complex containing trans PnBu3 and PPh3 ligands

The ruthenium(II) bis(acetate) complex Ru(CO)2(OAc)2(PnBu3)(PPh3) (OAc = acetate) containing two different trans phosphine ligands, has been employed as pre-catalyst for the chemoselective hydrogenation of a,b-unsaturated ketones to allylic alcohols. Analogous catalytic reactions with the homodiphosphine pre-catalysts Ru(CO)2(OAc)2(PnBu3)2 and Ru(CO)2(OAc)2(PPh3)2 gave lower conversions and selectivities. Batch catalytic reactions and operando high-pressure NMR experiments have contributed to establish that the hydrogenation of the C@O group is performed by the heterodiphosphine monohydride RuH(CO)2(OAc)(PnBu3)(PPh3) generated in situ by hydrogenation of the bis(OAc) precursor. PPh3 unfastening from this monohydride complex is an essential condition for the occurrence of catalytic activity.