Synthesis, Structure, and Electrochemical Studies of μ3222-C60 Triosmium Complexes

Two μ3222-C60 complexes, Os3(CO)8(PPh3)(μ3222-C60) (8) and Os3(CO)7(PMe3)23222-C60) (9), have been prepared by decarbonylation of Os3(CO)93222-C60) (6) with Me3NO/MeCN in the presence of phosphine ligands. The molecular structure of 8 has been determined by a single-crystal X-ray diffraction study. The structure of 8 is derived from that of Os3(CO)11(PPh3) by replacing three axial carbonyl ligands with a μ3-face-capping C6 ring of C60. The 13C NMR spectra (C60 region) of 6 and Os3(CO)8(PMe3)(μ3222-C60) (7) show 11 sp2 and 1 sp3 carbon resonances and 29 sp2 and 3 sp3 carbon resonances, respectively, which are consistent with C3v and Cs symmetric nature of the two complexes in solution. Electrochemical properties of 6, 7, and 9 have been studied by cyclic voltammetry (CV) in 1,2-dichlorobenzene (DCB) solutions. The general features of CV curves have revealed four reversible redox couples for 6 and 7 and three for 9 in the DCB potential window. The μ3222-C60 complexes, 6, 7, and 9, show a remarkable electrochemical stability compared to the known η2-C60 triosmium carbonyl complexes. The CV results suggest that a C60-mediated electron transfer to the triosmium center takes place in 6 and 7, but three successive C60-localized reductions occur in 9.