Synthesis, structure, and electrochemical studies of μ₃-η²,η²,η²-C ₆₀ triosmium complexes

Two μ₃-η²,η²,η²-C ₆₀ complexes, Os₃(CO)₈(PPh₃)(μ₃-η ²,η²,η²-C₆₀) (8) and Os₃(CO)₇(PMe₃)₂(μ ₃-η²,η²,η²-C ₆₀) (9), have been prepared by decarbonylation of Os₃(CO)₉(μ₃-η²,η ²,η²-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)(μ₃-η ²,η²,η²-C₆₀) (7) show 11 sp² and 1 sp³ carbon resonances and 29 sp² and 3 sp³ carbon resonances, respectively, which are consistent with C_3v and C_s 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 μ₃-η²,η²,η²-C ₆₀ 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.