New progress in the chemistry of stable metallaaromatic compounds of heavier group 14 elements.

By taking advantage of kinetic stabilization afforded by introduction of an efficient steric protection group, several kinds of silaaromatic compounds, such as silabenzene, 1- and 2-silanaphthalenes, and 9-silaanthracene, were successfully synthesized and isolated as stable compounds. The first stable germaaromatics, such as germabenzene and 2-germanaphthalene, were also synthesized by the use of a similar synthetic approach. Most of their molecular structures were definitively determined by X-ray crystallographic analysis. The novel molecular structures and unique reactivities of these metallaaromatic species are discussed on the basis of the experimental results together with those obtained by theoretical calculations, focusing on their aromaticity.