Synthesis, structure, and electrochemical studies of mu(3)-eta(2),eta(2),eta(2)-C-60 triosmium complexes

Abstract

Two mu(3)-eta(2),eta(2),eta(2)-C-60 complexes, Os-3(CO)(8)(PPh3)(mu(3)-eta(2),eta(2),eta(2)-C-60) (8) and Os-3(CO)(7)(PMe3)(2)(mu(3)-eta(2),eta(2),eta(2)-C-60) (9), have been prepared by decarbonylation of Os-3(CO)(9)(mu(3)-eta(2),eta(2),eta(2)-C-60) (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 Os-3(CO)(11)(PPh3) by replacing three axial carbonyl ligands with a mu(3)-face-capping C-6 ring of C-60. The C-13 NMR spectra (C-60 region) of 6 and Os-3(CO)(8)(PMe3)(mu(3)-eta(2),eta(2),eta(2)-C-60) (7) show 11 sp(2) and 1 sp(3) carbon resonances and 29 sp(2) and 3 sp(3) 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 mu(3)-eta(2),eta(2),eta(2)-C-60 complexes, 6, 7, and 9, show a remarkable electrochemical stability compared to the known eta(2)-C-60 triosmium carbonyl complexes. The CV results suggest that a C-60-mediated electron transfer to the triosmium center takes place in 6 and 7, but three successive C-60-localized reductions occur in 9.