Monocarbollide complexes of osmium: X-ray crystal structure of [Os(CO)3{η5-5-(NMe3)-7-CB10H10}]

In bromobenzene at reflux temperatures the compounds [Os3(CO)12] and [N(PPh3)2][nido-7-CB10H13] yield a mixture of the anionic tri- and mono-osmium complexes [Os3(CO)8(η5-7-CB10H11)]− and [Os(CO)3(η5-7-CB10H11)]−, respectively, characterized as their [N(PPh3)2]+ salts (2b, 3c). Protonation of 2b with HBF4·Et2O in thf (tetrahydrofuran) yields the hydrido cluster complex [Os3(μ-H)(CO)8(η5-7-CB10H11)] (4b), whilst treatment of 2b in the same solvent with CuCl and PPh3 in the presence of TlPF6 affords the bimetallic complex [Os3(μ-H)(CO)8{η5-10-Cu(PPh3)-7-CB10H10}] (5b). In contrast, the compounds [NHMe3][nido-7-CB10H13] and [Os3(CO)12] in refluxing bromobenzene give the novel zwitterionic complex [Os(CO)3{η5-5-(NMe3)-7-CB10H10}] (6). The structure of 6 was determined by X-ray crystallography, revealing an Os(CO)3 moiety η5-ligated by the carborane cluster in which, unusually, the NMe3 ligand is bonded to a boron atom on the upper B5 belt.