ELECTROCHEMICAL AND CHEMICAL GENERATION OF A MIXED-VALENT ORGANORHENIUM OXIDE AND ITS SUBSEQUENT AGGREGATION

Electrochemical one-electron reduction of the dinuclear d1-d1 organorhenium oxides Me4Re2O4 (1) and (c-Pr)4Re2O4 (2) reversibly yields the mono-anions 1- and 2-. Further electrochemical reduction is irreversible. The observed mechanisms upon electrochemical reduction and the involved electrode kinetics are discussed in the light of the electrochemical data. Chemical reduction by cobaltocene leads quantitatively to the same dinuclear radical complexes 1- and 2-, the EPR spectra of which support the formulation as Re(V)Re(VI) mixed-valence dimers. Reoxidation can be achieved with ferricinium hexafluorophosphate. Upon controlled exposure to oxygen the extraordinarily air-sensitive anion 1- forms the unprecedented linear trinuclear rhenium cluster [Cp2Co][Me6Re3O6] (4). The mechanism of this aggregation reaction involving disproportionation is discussed. The crystal and molecular structure of the anion 4 has been determined, the trimeric anion has almost C2v symmetry, and the Re-Re-Re angle is nearly linear (177.83(2)-degrees).