Redox isomerization of allylic alcohols in aqueous–organic biphasic systems catalyzed by water-soluble Ru(II)-N-heterocyclic carbene complexes

Allyl alcohols were isomerized to ketones or aldehydes in aqueous–organic biphasic systems using a water-soluble N-heterocyclic carbene complex [RuCl2L(η6-p-cymene)] (L = 1-butyl-3-methyl-imidazolin-2-ylidene, p-cymene = p-isopropyltoluene) for the first time. Hydrogen is needed to initiate the reaction and isomerization is accompanied by hydrogenation to the saturated alcohol. Initial turnover frequencies up to 65 mol product/mol catalyst · h were observed in neutral solutions at 80 °C. The reactions were strongly influenced by the pH of the aqueous phase. Addition of NaCl improved the total conversions and favoured isomerization on the expense of hydrogenation. The catalyst could be recycled in the aqueous phase for at least four times without a significant change in activity and selectivity.