ELECTROCATALYTIC HYDROGENATION ON POLY[RH-III(L)(2)(CL)(2)](+) (L=PYRROLE-SUBSTITUTED 2,2'-BIPYRIDINE OR 1,10-PHENANTHROLINE) FILMS ELECTRODES

The electrocatalytic hydrogenation (ECH) in aqueous electrolytes of cyclohexanone, substituted cyclohexanones, cryptone, dihydrocarvone and carvone has been performed on carbon felt electropolymerization of [Rh(L)(2)(Cl)(2)](+) complexes, in which L is a 2,2'-bipyridine (L=L(1) or L(3)) or a 1,10-phenanthroline (L=L(4)) substituted with pyrrole groups. The efficiency and the stability of these electrocatalytic materials, tested through the hydrogenation of millimolar amounts of substrates, depend on the nature of the linkage between the metal complex and the polymer skeleton. Turnovers around 5000 were reached with polymeric materials in which the complex is attached by an alkyl chain to the polypyrrolic matrix (L=L(1) or L(4)), without appreciable loss of catalytic activity. In contrast, L(3)-based materials appeared markedly less stable. This behaviour was attributed to the loss of complex molecules from the polymer film, due to hydrolysis of the carboxy-ester linkage. Regio- and stereoselectivity changes have been noted, according to the composition of the polymerized catalyst.