Structure of dialkyltin diaryloxides and their reactivity toward carbon dioxide and isocyanate

The synthesis, structure, and reactivity of dialkyltin diaryloxides, R2Sn(OAr)2 (R=Me, Bu; Ar=Ph, p-F-C6H4, p-t-Bu-C6H4), were investigated focusing on the differences between aryloxides and methoxides. Me2Sn(OAr)2 in the solid state formed a dimer. The aryloxo-bridged structure was confirmed by single crystal X-ray analysis. On the other hand, R2Sn(OAr)2 in solution easily dissociated upon dilution. The 119Sn-NMR spectra, especially for Me2Sn(OAr)2, exhibited two distinctly resolved signals assignable to the presence of isomeric five-coordinate environments. The reactivity of R2Sn(OAr)2 was much lower than that of R2Sn(OMe)2. Thus, R2Sn(OAr)2 did not react with carbon dioxide even at high pressure and excess amount of carbon disulfide. On the other hand, the reaction with p-methoxyphenyl isocyanate led to the corresponding aryl carbamates, suggesting the occurrence of an isocyanate insertion into the tin–oxygen bond of R2Sn(OAr)2.