Synthesis and structures of diaryloxystannylenes and -plumbylenes embedded in 1,3-diethers of thiacalix[4]arene.

New types of diaryloxystannylenes and -plumbylenes have been synthesized and structurally characterized. Lappert's diaminostannylene and -plumbylene E[N(SiMe3)2]2 (E = Sn, Pb) react with 1,3-diethers of tetrathiacalix[4]arene bearing benzyl or SiiPr3 groups to give the corresponding diaryloxystannylenes and -plumbylenes embedded in thiacalix[4]arene, respectively. X-ray diffraction analysis revealed that these tetrylenes exist as monomers in the solid-state. The structure of the thiacalix[4]arene scaffold is highly dependent on the substituents on the phenolic oxygen atoms. The benzyl derivatives adopt apparently C2-symmetric structures with a strong intramolecular SnOBn coordination, whereas the SiiPr3 derivatives have a distorted thiacalix[4]arene skeleton with relatively weak intramolecular EOSiiPr3 and ES interactions. On the basis of the 119Sn{1H} and 207Pb NMR studies in solution, the tin and lead atoms in the benzyl derivatives are strongly coordinated by the ethereal oxygen atoms, whereas those in the SiiPr3 derivatives are weakly coordinated by the bridging sulfur atoms or ethereal oxygen atoms. The tetrylene complexes of thiacalix[4]arene presented here do not show any isomerization in a temperature range from 20 to 110 °C, which is in sharp contrast to the fact that related diaryloxygermylenes and -stannylenes embedded in calix[4]arene underwent isomerization under heating conditions. This difference could be attributable to the ring size of thiacalix[4]arene larger than that of calix[4]arene.