Modelling nucleophilic substitution at silicon in solution using hypervalent silicon compounds based on 2-thiopyridones

Abstract

Halodimethylsilylmethyl derivatives of 2-thiopyridones have been prepared. The N–CH₂ isomer is favoured with the 6-methylthiopyridone. ¹³C and ²⁹Si chemical shifts have been used to calculate the extent of sulfur–silicon bond formation and the extent of pentacoordination. The results are consistent with the oxygen analogues and reveal that as expected sulfur is a poorer nucleophile than oxygen. The unsubstituted thiopyridone and the 5-trifluoromethyl derivative favour the S–CH₂ isomer. Again the mapping of nucleophilic substitution by nitrogen is in line with sulfur and oxygen nucleophiles, but in this series nitrogen is a poorer nucleophile than expected. The results are discussed in terms of steric strain, the preferences for alkylation of the pyridones and the bond strength of coordination to silicon.