Synthesis of Aromatic Species Containing a Heavier Group 14 Element by Taking Advantage of Kinetic Stabilization

In this Account, the syntheses, structures, and properties of novel aromatic species containing a heavier group 14 element were delineated with systematic comparison, focusing on their aromaticity. Several kinds of silaaromatic compounds, such as silabenzene, 1- and 2-silanaphthalenes, and 9-silaanthracene, which are a very interesting class of novel π-bonding systems containing a silicon atom, were successfully synthesized and isolated as stable compounds by taking advantage of the kinetic stabilization afforded by introduction of an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). A similar synthetic approach can be applied to the cases of the first stable germaaromatics, such as germabenzene and 2-germanaphthalene. The molecular structures of the newly obtained metallaaromatic species were systematically investigated based on X-ray crystallographic analysis and spectroscopic studies together with theoretical calculations. During this study, a variety of new reactivities for these metallaaromatic species were revealed and some new insights and deeper knowledge were obtained about the aromaticity of metallaaromatic compounds of heavier group 14 elements.