Reactions of Metal-Metal Multiple Bonds. 8. Forming Mo-Mo Quadruple Bonds by Reductive Elimination (Alkyl Group Disproportionation) in the Reactions of 1,2-Mo2R2(NMe2)4 Compounds (M triple bond M) with Carbon Dioxide and 1,3-Diary

摘要

Addition of either CO2 or 1,3-diaryltriazines to 1,2-Mo2R2(NMe2)4 compounds promotes reductive elimination from the dimetal center by alkyl group disproportionation with a concomittant metal-metal bond order change from three to four when R = an alkyl group having beta-hydrogen atoms. Both reactions proceed through intermediates of the form 1,2-Mo2R2(NMe2)2(chelate)2. The elimination of alkane and alkene is intramolecular and has a formal analogy with that found in mononuclear chemistry, namely beta-hydrogen elimination followed by reductive elimination by carbon-hydrogen bond formation. The detailed pathway leading to this is, however, uncertain. Finally, it should be recognized that it is not necessary to invoke the formation of an intermediate metal-hydride in these reactions. The beta-hydrogen atom of an ethyl ligand could be transferred to the alpha-carbon of the other ethyl ligand through the agency of one of the nitrogen atoms, which could be either a triazenido or dimethyl-amido ligand. In a formal sense this would have analogy with E2 reactions of substituted alkanes. These, and other possibilities, provide us with the stimulus for further studies of reductive eliminations of hydrocarbons from dinuclear metal centers.