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)] (<b>1</b>·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 <i>o</i>-methyl group on IMes, partial dehydrogenation of benzene, and subsequent coupling of the two unsaturated fragments to produce <b>2</b>. The abnormal NHC complex (<b>1</b>·aIMes) was also isolated. All compounds were characterized by spectroscopic studies and confirmed by X-ray crystallography.