DIASTEREOSELECTIVE GAS-PHASE CARBON-CARBON BOND ACTIVATION MEDIATED BY BARE CO+ CATIONS

The unimolecular decompositions of 5-methylheptanenitrile (1), 6-methy loctanenitrile (2), and 7-methylnonanenitrile (3) complexed to bare Co + cations have been investigated by means of tandem mass spectrometry. Extensive regio- and diastereospecific labeling experiments were cond ucted to gain further insight into the mechanistic details, in particu lar the stereoselectivity of the Co+-induced demethanation in the gas phase. The overall reaction follows a 1,2-elimination mode, and, with regard to the regiospecificity, the neutral methane originates exclusi vely from the (omega-2) and (omega-1) positions of the alkyl chain. Fo r 2 and 3 the examination of diastereospecifically labeled isotopomers reveals that the gas-phase demethanation exhibits a remarkable diaste reoselectivity. This unprecedented example for a stereoselective C-C b ond activation in gas-phase oganometallic chemistry can be accounted f or in terms of steric features of the metallacyclic intermediates.