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

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Various η 2 -C 60 and μ 3 -η 2,η 2,η 2 -C 60 triosmium carbonyl cluster complexes Os 3 (CO) 11 (η 2 -C 60 ) ( 1 ), Os 3 (CO) 10 (NCMe)(η 2 -C 60 ) ( 2 ), Os 3 (CO) 10 (PPh 3 )(η 2 -C 60 ) ( 3 ), Os 3 (CO) 9 (PR 3 ) 2 (η 2 -C 60 ) ( 4, R = Ph; 5, R = Me), Os 3 (CO) 9 (μ 3 -η 2,η 2,η 2 -C 60 ) ( 6 ), and Os 3 (CO) 8 (PMe 3 )(μ 3 -η 2,η 2,η 2 -C 60 ) ( 7 ) have been isolated as crystalline solids and characterized by spectroscopic (IR, MS, and 1 H, 31 P, and 13 C 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 Os 3 (CO) 12 by replacing an equatorial carbonyl ligand with an η 2 -C 60 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 13 C NMR spectra of 2a and 5 indicate that both complexes undergo similar fluxional processes of restricted equilibration of in-plane equatorial C 60 and carbonyl ligands via a triply bridged intermediate with identical values of Δ G c ⧧ = 12.7 ± 0.1 kcal/mol. Thermolysis of 2 in refluxing chlorobenzene affords Os 3 (CO) 9 (μ 3 -η 2,η 2,η 2 -C 60 ) ( 6 ) in 23% yield, which can be alternatively prepared in 32% yield from the reaction of Os 3 (CO) 10 (NCMe) 2 (2 equiv) and C 60 (1 equiv). Decarbonylation of 6 with Me 3 NO/MeCN reagent in the presence of excess PMe 3 gives Os 3 (CO) 8 (PMe 3 )(μ 3 -η 2,η 2,η 2 -C 60 ) ( 7 ) in a quantitative yield. VT 13 C NMR spectra of both 6 and 7 reveal a localized-3-fold rotation of carbonyl and phosphine ligands on each osmium center.