Cyanohydrin Hydration with [Ru(η6-p-cymene)Cl2PR3] Complexes

The catalytic hydration of cyanohydrins to their corresponding alpha-hydroxyamides provides a route to industrially useful alpha-hydroxy amides, alpha-hydroxy esters, alpha-hydroxy carboxylic acids, and their acrylic derivatives. However, until now, no homogeneous nitrile hydration catalyst has been capable of complete conversion of cyanohydrins to their corresponding amides because cyanohydrins degrade to produce cyanide, which poisons the catalyst. Because the cyanohydrin degradation is an equilibrium process, it was hypothesized that a faster nitrile hydration catalyst would be capable of hydrating the cyanohydrin before degradation occurs. Secondary coordination sphere effects were used to develop a faster catalyst based on the [Ru(eta(6)-arene)Cl-2(PR3)] scaffold. A series of [Ru(eta(6)-p-cymene)Cl-2(PR3)] complexes, where R = NMe2, OMe, Et, was synthesized, and their activity toward cyanohydrin hydration was determined. The complex [Ru(eta(6)-p-cymene)Cl-2(P(NMe2)(3))] is an excellent catalyst, and the unprecedented complete conversion of a cyanohydrin to its corresponding amide using a homogeneous catalyst was achieved with glycolonitrile and lactonitrile.