ELECTROCHEMICAL REDUCTION OF THE BIS(CYCLO-OCTADIENE)RHODIUM MONOCATION - GENERATION AND FATE OF THE 17-ELECTRON RADICAL

The electrochemical reduction of the monocation of bis-(cyclo-octadien e)Rh[(CODRh+] has been studied in chlorinated hydrocarbons and d(6)-ac etone by cyclic voltammetry, chronoamperometry and exhaustive coulomet ry. Successive one-electron reductions are observed for the couples (C ODRh+/(COD)(2)Rh and (COD)(2)Rh/(CODRh- at -1.34 V vs. Fc and -1.93 V vs. Fc respectively. The 17-electron Rh(0) radical (COD)(2)Rh abstract s a Cl atom from CH2Cl2 to give the dinuclear complex [(COD)Rh(mu-Cl)] (2) in high yield at 298 K. At subambient temperatures this reaction i s suppressed and the dominant decomposition product is apparently (COD )Rh(C8H13), formed by H atom abstraction by (COD)(2)Rh from solvent an d/or adventitious water. Electrolysis products were characterized by e lectron spin resonance (ESR), nuclear magnetic resonance (NMR) and mas s spectrometry. The reactivity of the radical is rationalized by a bon ding model in which the lowest unoccupied molecular orbital (LUMO) is d(x2-y2) with some diolefin mixing. ESR measurements are consistent wi th this model and suggest that the COD ligands form a ligand field aro und Rh which is closer to square planar than to tetrahedral.