Synthesis and Characterization of η²-C₆₀ and μ₃-η²,η²,η²-C₆₀ Triosmium Cluster Complexes

Abstract

Various η2-C60 and μ3-η2,η2,η2-C60 triosmium carbonyl cluster complexes Os3(CO)11(η2-C60) (1), Os3(CO)10(NCMe)(η2-C60) (2), Os3(CO)10(PPh3)(η2-C60) (3), Os3(CO)9(PR3)2(η2-C60) (4, R = Ph; 5, R = Me), Os3(CO)9(μ3-η2,η2,η2-C60) (6), and Os3(CO)8(PMe3)(μ3-η2,η2,η2-C60) (7) have been isolated as crystalline solids and characterized by spectroscopic (IR, MS, and 1H, 31P, and 13C NMR) and analytical data. The molecular structure of complex 1 has been determined by a single-crystal X-ray diffraction study. The structure of 1 is derived from that of Os3(CO)12 by replacing an equatorial carbonyl ligand with an η2-C60 ligand coordinated through a 6−6 ring fusion. The structural assignment of 2−7 is made on the basis of spectroscopic results. Compound 2 exists as two isomers in solution in a ratio of 2:1 (2a:2b). VT 13C NMR spectra of 2a and 5 indicate that both complexes undergo similar fluxional processes of restricted equilibration of in-plane equatorial C60 and carbonyl ligands via a triply bridged intermediate with identical values of ΔGc⧧ = 12.7 ± 0.1 kcal/mol. Thermolysis of 2 in refluxing chlorobenzene affords Os3(CO)9(μ3-η2,η2,η2-C60) (6) in 23% yield, which can be alternatively prepared in 32% yield from the reaction of Os3(CO)10(NCMe)2 (2 equiv) and C60 (1 equiv). Decarbonylation of 6 with Me3NO/MeCN reagent in the presence of excess PMe3 gives Os3(CO)8(PMe3)(μ3-η2,η2,η2-C60) (7) in a quantitative yield. VT 13C NMR spectra of both 6 and 7 reveal a localized-3-fold rotation of carbonyl and phosphine ligands on each osmium center.