Aromaticity/Antiaromaticity in 'Bare' and 'Ligand-Stabilized' Rings of Metal Atoms

摘要

During the last decade, the aromaticity/antiaromaticity of "bare" and "ligand-stabilized" rings of metal atoms has flourished reaching a high level of sophistication. Compared to the aromaticity/antiaromaticity encountered in organic rings, primarily being of the traditional π-type, "bare" and "ligand-stabilized" rings of metal atoms can exhibit a multifold aromaticity/antiaromaticity and conflict-ing aromaticity, arising from the electron delocalization of s, p, d, and even f orbitals of the ring atoms. In this context we can speak for ó-, π-, δ-, and ψ-aromaticity/antiaromaticity as well as for double (ó + π) and even triple (ó + π + δ ) aromaticity (possible in rings of transition metal atoms) and any possible combi-nation of the ó-, π-, δ-, and ψ-types of aromaticity/antiaromaticity. The f-orbital and possibly ψ-aromaticity can exist only in rings of lanthanide and actinide metal atoms. In view of these facts, in this review we have provided an overview and updated information about aromaticity/antiaromaticity of rings of metal atoms covering the most significant developments in this new emerging field.