(Pentamethylcyclopentadienyl) (polypyridyl) rhodium and iridium complexes as electrocatalysts for the reduction of protons to dihydrogen and the hydrogenation of organics

The ability of [(eta(5)-Me-5)M-III(L)Cl](+) complexes (M = Rh and Ir, L = 2,2'-bipyridine and 1,10-phenanthroline) to act as electrocatalysts for the hydrogenation of unsaturated organic substrates has been examined in homogeneous acetonitrile solution, using formic acid as a proton source, as well as in aqueous electrolytes with electrodes modified by oxidative electropolymerization of pyrrole-substituted Rh(III) and Zr(III) complexes. The hydrogenation process involves the formation of an electrogenerated hydride complex, followed by the insertion of the substrate in the metal-hydride bond, It appears that rhodium complexes are better catalysts than the iridium ones, and that their immobilization onto an electrode surface decreases their catalytic activity. (C) 1997 Elsevier Science S.A.