The C-60-triosmium carbonyl complexes Os-3(CO)(11-n)(PPh3)(n)(eta(2)-C-60) [n = 0 (1), n = 1 (2), n = 2 (3)] have been studied by both cyclic voltammetric and IR spectroelectrochemical methods in a dichloromethane-toluene (4:1) solution. Both results suggest that a C-60-mediated electron transfer to the triosmium metal center takes place in these complexes. This is further confirmed by the synthesis and characterization of [NiCp2’](+)1(-) (Cp’ = eta(5)-C5Me5). The three sequential one-electron reduction potentials of 1-3 are in the order of 1 > 2 > 3, respectively, due to the donor effect of the PPh3 ligand. Reduction is accompanied by loss of the C-60 moiety.