The first example of tetraosmium carbonyl clusters containing (m3-NH) nitrene ligands: syntheses and crystal structures

Abstract

The reaction of [Os4(μ-H)4(CO)12] with o-tert-butylhydroxylamine hydrochloride (tBuONH2·HCl) in the presence of trimethylamine-N-oxide (Me3NO) in dichloromethane afforded [Os4(μ-H)4(CO)11{η1-NH2OtBu}] (1) in high yield. Upon the addition of tetrafluoroboric acid (HBF4) into the solution of 1 in acetonitrile, the novel cationic cluster [Os4(μ-H)4(CO)11(μ-NH2)(NCMe)][BF4] (2) formed. Reaction of 1 with HBF4 in the presence of diphenylacetylene gave two geometric isomers, [Os4(μ-H)2(CO)11(μ-NH2){μ-η3-Ph(CHC)Ph}] (3) and [Os4(μ-H)2(CO)11(μ-NH2)(η1-Ph(CHC)Ph)] (4). Treatment of 2 with excess Me3NO in acetonitrile gave [Os4(μ-H)4(CO)10(μ-NH2)(NCMe)2][BF4] (5). The carbonylation of 2 in the refluxing chloroform afforded the neutral clusters [Os3(μ-H)2(CO)9(μ-NH2)Cl] (6) and [Os4(μ-H)3(CO)12(μ-NH2)] (7). Protonation of 7 with trifluoromethylsulfonic acid, CF3SO3H, gave another cationic cluster, [Os4(μ-H)4(CO)12(μ-NH2)][CF3SO3] (8), which is an analogue of 2. Refluxing of 7 in toluene under an argon atmosphere afforded [Os4(μ-H)2(CO)12(μ3-NH)] (9), which is the first example of (μ3-NH) nitrene ligands containing tetraosmium carbonyl clusters. The solid-state structures of 2−9 were established by X-ray analysis. The 1H NMR properties of these clusters were studied, and a correlation between the chemical shift and the structural geometry was established.