Synthesis, structure, and fluxional properties of osmium cluster [(OC)4(tert-BuNC)Os]Os3(CO)11. Evidence for restricted rotation about a metal-metal bond

The cluster Os 4 (CO) 15 (CNBu t ) has been prepared by the addition of Bu t NC to OS 4 (CO) 15 in CH 2 Cl 2 at 0 o C. The structure has been solved by X-ray crystallography: space group P2/a with a=15.946 (2) A, b=11.465 (2) A, c=16.776 (2) A, β=92.09 (1) o , V=3064.8 A 3 , Z=4; R 1 =0.51, R 2 =0.057 for 2163 observed reflections; there is a partial molecule of CH 2 Cl 2 that is disordered