Abstract
The electrochemical reduction of the monocation of bis-(cyclo-octadiene)Rh[(COD)2Rh+] has been studied in chlorinated hydrocarbons and d6-acetone by cyclic voltammetry, chronoamperometry and exhaustive coulometry. Successive one-electron reductions are observed for the couples (COD)2Rh+/(COD)2Rh and (COD)2Rh/(COD)2Rh− at -1.34 V vs. Fc and -1.93 V vs. Fc respectively. The 17-electron Rh(0) radical (COD)2Rh abstracts a Cl atom from CH2Cl2 to give the dinuclear complex [(COD)Rh(μ-Cl)]2 in high yield at 298 K. At subambient temperatures this reaction is suppressed and the dominant decomposition product is apparently (COD)Rh(C8H13), formed by H atom abstraction by (COD)2Rh from solvent and/or adventitious water. Electrolysis products were characterized by electron spin resonance (ESR), nuclear magnetic resonance (NMR) and mass spectrometry. The reactivity of the radical is rationalized by a bonding model in which the lowest unoccupied molecular orbital (LUMO) is dx2−y2 with some diolefin mixing. ESR measurements are consistent with this model and suggest that the COD ligands form a ligand field around Rh which is closer to square planar than to tetrahedral.
Published Version
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