Selective Hydrogenation of α, β-Unsaturated Carbonyl Compounds and Nitriles Catalyzed by Polymer-supported Rhodium Carbonyl Complexes

Abstract

The hydrogenation of α, β-unsaturated carbonyl compounds and nitrile with carbon monoxide and water was investigated by using rhodium carbonyl cluster catalysts supported on resin beads containing polymer-bound amine moieties. The hydrogenation proceeded heterogeneously in dioxane-hexane (3:7) and no reaction took place in the solution after separation of the catalyst beads. However, rhodium species partially migrated during the reaction from the resin beads to the solution in tetrahydrofuran.
Amberlite IRA-93 and Amberlyst A-21, macrore cticular beads having N, N-dimethylbenzylamine moieties, were found to be the most excellent supports among the ion-exchange resins examined in terms of high activity and easy handling. Results of the hydrogenation with the catalyst supported on Amberlyst A-21 are shown in Table 1.
The carbon-carbon double bonds of α, β-unsaturated carbonyl compounds and nitrile were selectively hydrogenated and adjacent carbonyl and cyano groups were intact, although formyl group was hydrogenated to the corresponding alcohol. Simple aldehydes such as benzaldehyde and butyraldehyde were also hydrogenated to alcohols under these conditions.
The resin-supported catalysts were stable under nitrogen or carb on monoxide atmosphere and could be reused without any appreciable loss in catalytic activity and selectivity, as shown in Table 2. The effect of substitution with bulky groups or the number of substituents on the hydrogenation rates of olefins was more pronounced in the heterogeneous system than in homogeneous system (Table 3). The rates with the resin-supported catalysts were generally greater than those with the homogeneous catalyst (Table 4). Although the active species could not yet be identified, rhodium carbonyl cluster anions were detected in the reaction. It is believed that the first step probably involves the formation of a cluster anion from Rh₄(CO)₁₂ and the anion is bound to the resin to form heterogeneous catalyst.