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

The electrocatalytic hydrogenation (ECH) in aqueous electrolytes of cy clohexanone, 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) o r L(3)) or a 1,10-phenanthroline (L=L(4)) substituted with pyrrole gro ups. The efficiency and the stability of these electrocatalytic materi als, tested through the hydrogenation of millimolar amounts of substra tes, depend on the nature of the linkage between the metal complex and the polymer skeleton. Turnovers around 5000 were reached with polymer ic 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 cat alytic activity. In contrast, L(3)-based materials appeared markedly l ess stable. This behaviour was attributed to the loss of complex molec ules from the polymer film, due to hydrolysis of the carboxy-ester lin kage. Regio- and stereoselectivity changes have been noted, according to the composition of the polymerized catalyst.