Expansion of the Concept of Aromaticity by the Introduction of Heavy Atoms and Application to Coordination Chemistry

Aromaticity to explain unique properties of benzene derivatives has long played an important role in chemistry. To expand the aromatic world, replacement of skeletal carbon atoms in the aromatic compounds by silicon and germanium atoms was performed and aromaticity of the resulting silicon- and germanium-bearing compounds has been established. Based on the background, we decided to undertake investigation on whether or not introduction of tin and lead atoms into the aromatic skeletons would retain the aromaticity. We herein summarize our recent project on the synthesis of tin- and lead-bearing aromatic compounds, dilithiostannoles and a dilithioplumbole. Application of the dianionic aromatic compounds as ligands for transition-metal complexes is also demonstrated.