Silylotropy in 4-substituted N-trimethylsilylpyrazoles is studied by d
ynamic H-1, C-13, and Si-29 NMR spectroscopy. The catalytic 1,2-migrat
ion of a trimethylsilyl group in 4-halo-N-trimethylsilylpyrazoles was
detected. Silylotropy in N-trimethylsilylpyrazoles in the presence of
halogens or trimethylhalosilanes is believed to proceed through format
ion of N,N'-bis(trimethylsilyl)pyrazolium salts, the barrier of silylo
tropy in pyrazoles being markedly reduced.