Gas-Phase Reactions of H3Si- and Me3Si-. The formation of Si-O and Si-S Bonds. A Flowing Afterglow and ab Initio Study

Article abstract of DOI:10.1021/ja00281a055

The ions H3Si^- and Me3Si^- undergo Si-O and/or Si-S bond forming reactions with CO2, COS, CS2, SO2, N2O, MeNCO, and MeNCS forming H3SiO3^-, Me3SiO^-, H3SiS^-, or Me3SiS^- ions as appropriate.The rates of these reactions vary markedly, e.g., the reaction of H3Si^- with CS2 (to form H3SiS^- + CS) occurs at every encounter, whereas that of H3Si^- with N2O (to form H3SiO^- plus N2) occurs for only one in every thousand collisions.Ab initio calculations (at 6-31G level) for the reactions of H3Si^- with CO2, CS2, SO2, and N2O suggest different and complex reaction pathways.The reaction of H3Si^- with CO2 is characterized by initial approach to carbon, and subsequent rearrangements are required to form H3SiO^-.H3SiS^- is formed by a simple path from CS2 following initial attack at sulfur.H3Si^- reacts with SO2 in alternative ways to form five-coordinate intermediate which subsequently decomposes to H3SiO^- plus SO.H3Si^- is likely to attack N2O at the terminal nitrogen, and subsequent rearrangement forms H3SiO^-.The length, or complexity of the reaction pathway appears inversely related to the measured efficiency in the majority of reactions.