TRANSFER HYDROGENOLYSIS OF ARYL HALIDES AND OTHER HYDROGEN ACCEPTORS BY FORMATE SALTS IN THE PRESENCE OF PD/C CATALYST

The Pd/C-catalyzed transfer hydrogenolysis of aryl halides by formate salts in a triphase system requires the absorption of all three substrates, the aryl halide acceptor, the formate anion, and the water, to a single site on the catalyst surface in a specific order. This unique mechanism necessitates delicate optimization of reaction conditions. The affinity of various hydrogen acceptors to the catalyst was determined by competitive kinetic experiments to be in the decreasing order: iodobenzene > phenylacetylene > styrene > bromobenzene > nitrobenzene > chlorobenzene > fluorobenzene. The rate-determining step in the overall transfer-hydrogenation process is the adsorption of the donors to the catalyst.