Probing the Aromaticity of Unsaturated N-heterocyclic Carbenes and Their Heavy Analogues with the EDDB Criterion

Three series of N-heterocyclic carbene analogues including Arduengo-type systems (HCNBut)2E (1; E = C, Si, Ge, Sn), their benzannulated derivatives C6H4(NCH2But)2E (2; E = C, Si, Ge, Sn, Pb), and amidophenolates C6H2But2(O)NButE (3; E = Ge, Sn, Pb) were studied by the electron density of delocalized bonds (EDDB) method. The results obtained confirmed the π-aromaticity of systems 1–3. The aromaticity series were obtained. The degree of aromaticity of heavy carbene analogues increases on going down Group 14 of the periodic system.