An ab initio and ion cyclotron resonance study of the reactions between alkoxide negative ions and silane systems. Stable adduct formation, and nucleophilic displacement reactions

Abstract

Ab initio LCAO-MO-SCF calculations suggest that reaction of HO-(or MeO-) with silane should proceed through a stable trigonal bipyramidal adduct. Reaction of alkoxide anions with a variety of alkylsilanes in an i.c.r. spectrometer leads to (i) nucleophilic displacement reactions, (ii) stable adducts, (iii) decomposing adducts which collapse to tetrahedral anions by elimination of a neutral molecule, and (iv) proton abstraction reactions. The nucleophilic displacement reaction between MeO- and Me3SiR has been used to produce a variety of R- species, including the allyl, propargyl and benzyl anions. The reactions of these ions with methyl nitrite have been used to show that (i) the benzyl anion does not undergo benzylic hydrogen/phenyl hydrogen scrambling prior to reaction, (ii) the allyl anion reacts as a symmetrical species, and (iii) that hydrogen scrambling does not occur in the propargyl anion, and that C3H3- may either react as HC≡C-CH2- or -HC=C=CH2.