Rate studies of silylation with silylamides

Abstract

The rates of silylation of p-nitrophenol with N,O-bis(trialkylsilyl)acetamides in dioxane have been measured, the reaction shown to be slowed down by replacing methyl by ethyl in the trialkylsilyl group. The rates of methanolysis of some N,O-bis(aryldimethylsilyl)acetamides (I) and N-aryldimethylsilylacetamides (II) have been measured. The reactions of compounds II were found to be acid catalyzed and accelerated by electron-withdrawing substituents in the benzene ring. At 30°C the methanolysis was shown to be entropy controlled. Compounds of series I were found to be aproximately 1000 times more reactive than those of series II. Introducing a methyl at nitrogen in the monosilylamides produced a similar rate enhancing effect as introduction of a second silyl group. Promotion of ( p-d)π coordination of silicon to oxygen or nitrogen in the ground state of the silylamide molecule is suggested as the factor responsible for this effect.