ELECTRON-TRANSFER AND CHLORIDE LIGAND DISSOCIATION IN COMPLEXES [(C(5)ME(5))CLM(BPY)](+) [(C(5)ME(5))M(BPY)](N) (M=CO, RH, IR, N=2+,+,0,-) - A COMBINED ELECTROCHEMICAL AND SPECTROSCOPIC INVESTIGATION/

In contrast to the rapid and chemically reversible two-electron ECE' r eductive elimination reaction [(C(5)Me(5))ClM(bpy)](+) + 2e(-) --> (C( 5)Me(5))M(bpy) + Cl-, M = Rh or Ir, the analogous cobalt system exhibi ts two separate one-electron steps (EC + E' process) with a persistent , EPR-spectroscopically characterized cobalt(II) intermediate [(C(5)Me (5))Co(bpy)](+). Within the series of coordinatively unsaturated homol ogous species (C,Me,)M(bpy), the cobalt derivative exhibits the smalle st and the iridium homologue the largest metal(I)-to-bpy electron tran sfer in the ground state, as evident from electrochemical potentials a nd long-wavelength absorption data. A comparison within that homologou s series indicates why the rhodium system, with its intermediate posit ion, is most suitable for hydride transfer catalysis.