Redox behavior of the molybdenum and tungsten metallafullerenes M(η2-C60)(CO)2(phen)(dbm) (phen = 1,10-phenanthroline; dbm = dibutyl maleate):: (spectro)electrochemistry and theoretical considerations

Electrochemistry of M(eta(2)-C-60)(CO)(2)(phen)(dbm) (M = W 1, Mo 2; phen = 1,10-phenanthroline; dbm = dibutyl maleate) shows that the complexes undergo four sequential reduction processes. As with foe C-60, the first three electrons add reversibly (even if the relevant potentials are shifted ca. 0.15 V toward negative values), whereas the fourth reduction features chemical irreversibility. Cyclic voltammetry gives evidence that, as a consequence of the latter process, the metal fragment decomplexes and [C-60](3-) is released. In good agreement with this picture, a qualitative MO approach shows four close LUMOs for the ground state structure of the uncharged complexes. The first three levels are delocalized over C-60 (somewhat extended to the dmb pi system), while the fourth one is metal-fullerene antibonding (back donation d(n) --> pi* C-60) and its occupation causes fulleride dissociation. The EPR spectra of the electrogenerated [1](-) and [2](-) monoanions are significantly different from that of [C-60](-) and seem suggestive of metal character for these radical species. At present, this result is unexpected in that the unpaired electron in the anions [1](-) and [2](-) should be intuitively centered on the coordinated fullerene.