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

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