Migration of the trimethylsilyl group in silylated acylamides

Abstract

Variable temperature n.m.r. studies were made for several N-trimethylsilylacylamides R1CO·N(SiMe3)R2(R1= alkyl or aryl, R2= Ph or Me). Based on the careful determination of the values of J29Si–H for the CH3–N proton signals in the case of PhCO·NMe(SiMe3) the non-equivalence of the trimethylsilyl 1H resonances was explained in terms of 1,3-migration of the trimethylsilyl group between the nitrogen and oxygen atoms. A study of the variation of the coalescence temperatures and the activation energies for eight N-phenyl-N-trimethylsilylacylamides RCO·NPh(SiMe3), showed that the basicity of the amide largely determined the rate of 1,3-migration of the trimethylsilyl group.