GAS-PHASE CHEMISTRY OF THE SILAFORMAMIDE ION

The anion [HSi(O)NH](-) (2) has been produced in the source region of a tandem flowing afterglow selected ion flow tube from phenylsilane, a mide, and water and mass-selected for further study. Its connectivity has been established from studies of its formation from deuterated rea ctants and by chemical reactivity studies with CO2, COS, and CS2. A va riety of alcohols undergo interesting reactions with 2. In particular, reactions with fluoro alcohols are considered in terms of the energy content of the complex formed when a proton is transferred from a fluo roalcohol to 2. A series of anions related to 2 have been studied by a b initio methods. For a number of these, the silylene anion form is mo re stable than its isomer (e.g. [Si(O)NH2](-) (1) is more stable than [HSi(O)NH](-) (2)). Computational energies suggest that Si-H deprotona tion of HSi(X)Y (for X = O, NH, CH2) when Y = NH2, CH3 is favored over deprotonation at N-H or C-H, while O-H deprotonation is favored when Y = OH. Charge density computations of a variety of neutrals and anion s reveal the dominant effect of silicon in determining charge density. The acidity (Delta G(acid)) Of silaformamide has been estimated by br acketing methods to be between 350 and 355 kcal mol(-1).