Mechanism and product characterization from the electroreduction of heterodinuclear complexes [(C5Me5)ClM(μ-L)Re(CO)3X](PF6),M=Rh or Ir, L-2,2′-azobispyridine or 2,2′-azobis(5-chloropyrimidine), X = halide

The title compounds are easily reduced to paramagnetic neutral species [(C5Me5)ClM(mu-L)Re(CO)(3)X](.) which were characterized as complexes of L.-. On further electron addition the M-bound chloride is dissociated slowly to yield [(C5Me5)M(mu-L)Re(CO)(3)X], distinguished by intense low-energy charge transfer bands. Addition of a third electron causes this band to shift and diminish in intensity. Cyclic voltammetry, UV-Vis-NIR and IR spectroelectrochemistry as well as EPR at 9.5 and 285 GHz were used to establish the (E, EC, E) process sequence of electroreduction and to identify the products. The significance of these results for potential applications in catalysis is discussed. (C) 2004 Elsevier B.V. All rights reserved.