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

Electrochemical one-electron reduction of the dinuclear d1-d1 organorh enium oxides Me4Re2O4 (1) and (c-Pr)4Re2O4 (2) reversibly yields the m ono-anions 1- and 2-. Further electrochemical reduction is irreversibl e. The observed mechanisms upon electrochemical reduction and the invo lved electrode kinetics are discussed in the light of the electrochemi cal data. Chemical reduction by cobaltocene leads quantitatively to th e same dinuclear radical complexes 1- and 2-, the EPR spectra of which support the formulation as Re(V)Re(VI) mixed-valence dimers. Reoxidat ion can be achieved with ferricinium hexafluorophosphate. Upon control led exposure to oxygen the extraordinarily air-sensitive anion 1- form s the unprecedented linear trinuclear rhenium cluster [Cp2Co][Me6Re3O6 ] (4). The mechanism of this aggregation reaction involving disproport ionation is discussed. The crystal and molecular structure of the anio n 4 has been determined, the trimeric anion has almost C2v symmetry, a nd the Re-Re-Re angle is nearly linear (177.83(2)-degrees).