Tetraosmium carbonyl clusters containing µ-NH2 amido ligands: syntheses, crystal structures and reactivities

Abstract

Treatment of [Os4(μ-H)4(CO)12] with O-tert-butylhydroxylamine hydrochloride (tBuONH2·HCl) afforded two amino ligand containing osmium clusters [Os4(μ-H)4(CO)11(η1-NH2OtBu)] (1) and [Os4(μ-H)4(CO)11{(μ-H)3Os(CO)2(η1-NH2OtBu)2Cl}] (2) in moderate yields. For the same reaction, in the presence of one equivalent of [Os3(CO)12], the novel heptaosmium carbonyl cluster [{Os4(μ-H)2(CO)11(μ-NH2)}{Os3(μ-H)(CO)11}] (3) was isolated together with 1 and 2. This heptaosmium cluster 3 displays an uncommon metal skeleton, where the tetraosmium tetrahedron and the triosmium triangle are connected by a metal–metal bond. Upon the addition of hydrobromic acid (HBr) to a solution of 1, a pair of geometric isomers, unsupported butterfly [Os4(μ-H)4(CO)11(μ-NH2)Br] (4a) and supported butterfly [Os4(μ-H)4(CO)11(μ-NH2)Br] (4b) clusters were formed. They are the first examples of μ-NH2 amido tetraosmium carbonyl clusters, which serve as good models for the adsorbed nitrogen atoms on a stepped metal surface. Refluxing of 4a in toluene for several hours, afforded a new triosmium μ-NH2 amido cluster [Os3(μ-H)2(CO)9(μ-NH2)Br] (5). Addition of an excess of triphenylcarbenium tetrafluoroborate [Ph3C][BF4] to a solution of 4a in dichloromethane gave another tetrahedral μ-NH2 amido tetraosmium cluster [Os4(μ-H)2(CO)11(μ-NH2)Br] (6) in moderate yield upon elimination of two hydrides.