Normal and Abnormal NHC Coordination in [Os₄(μ-H)₄(CO)₁₁(IMes)] and Exhaustive Dehydrogenation of an IMes Methyl Group

The osmium cluster [Os4(μ-H)4(CO)11(IMes)] (1·nIMes) was prepared by treatment of IMesAgCl with [Os4(μ-H)4(CO)12]. The product of this reaction is believed to be the first tetranuclear NHC cluster compound. Thermolysis of this complex in benzene at reflux resulted in exhaustive dehydrogenation of an o-methyl group on IMes, partial dehydrogenation of benzene, and subsequent coupling of the two unsaturated fragments to produce 2. The abnormal NHC complex (1·aIMes) was also isolated. All compounds were characterized by spectroscopic studies and confirmed by X-ray crystallography.