ORGANOMETALLIC MIXED-VALENT IONS WITH D(7)D(8) AND D(8)D(9) ELECTRONIC CONFIGURATIONS DERIVED FROM (FULVALENEDIYL)CO-2(COD)(2)

The dinuclear complex (fulvalenediyl)Co-2(1,5-C8H12)(2) (FvCo(2)(COD)( 2)), 5, has four one-electron redox reactions in the potential range 1.0 to -3.1 V vs ferrocene, three of which are chemically reversible. Two oxidations are observed with formal potentials of -0.300 and -0.07 2 V, the E degrees separation of 228 mV being diagnostic of a moderate M-M interaction. ESR spectra of the d(7)d(8) mixed-valent monocation 5(+) show that it is valence trapped. The reduction 5/5(-) has a forma l potential of -2.86 V. The d(8)d(9) monoanion 5(-) produced by Na/K r eduction of 5 in THF is also valence trapped according to ESR spectros copy. The series 5(+)/5/5(-) is the first one in which two different m ixed-valent states are characterized for a single fulvalenediyl-bridge d complex.