ELECTROCHEMICAL OXIDATION OF RHENIUM ALKYL COMPLEXES OF THE TYPE [RE(ETA-C5H5)(NO)(PPH3)R] - IMPLICATIONS FOR THE MECHANISM OF HYDRIDE ABSTRACTION BY PH3C+PF6-
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abstract
Electrochemical oxidation of 12 rhenium alkyls of the type [Re(-C5H5)(PPh3)(NO)R] has been examined as part of an investigation into the possibility that hydride abstraction from these substrates by Ph3C+PF6- involves an electron-transfer mechanism. Cyclic voltammograms of each complex exhibit a single oxidation between +300 and +500 mV (vs. SCE) that is partially reversible chemically. Substituent effects for this oxidation suggest that the complexes fall into two categories which have different base potentials while potentials within each group follow the expected inductive trends. Controlled potential coulometry establishes that exhaustive oxidation of both types is a two-electron process, but differences in the observed Ep values suggest that type I and type II complexes are undergoing ECE and EEC processes, respectively. This is confirmed by comparison of the current functions observed for oxidation of the complexes. Most of the complexes are slightly harder to oxidize in CH2Cl2 than the trityl radical, implying that it would not be feasible to trap thermally any odd-electron intermediates formed during hydride abstraction from these substrates. No correlation is observed between the potentials at which the complexes oxidize and the selectivity for - or -hydride abstraction from type I complexes. 1985 American Chemical Society.
