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

The ability of (η⁵-C₅Me₅)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 Ir(III) complexes. The hydrogenation process involves the formation of an electrogenerated hydrido 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.