Chemistry of mixed sulfur-, selenium-, or tellurium- and silicon-, or tin-containing heterocycles

Lone pair ionization energies for 1,5-dichalcogenocanes containing endocyclic 3,7-R2Si groups and the parent 1,5-dichalcogenocanes, estimated from the TCNE charge-transfer wavelength maxima, are in good agreement with ionization energies directly obtained from photoelectron spectroscopy. These data indicate the occurrence of substantial intra-annular interaction between the chalcogen atoms and silyl groups, consistent with the well-known beta-effect of silicon and the novel beta-disilyl effect, when R (in R2Si) is Me3Si.