Heavier Benzene-1,4-diides: Merging Aromatics and Metallylenes

Heavier benzene (i. e. Group 14 aromatics) and carbene analogues (i. e. metallylenes) have been intriguing species in fundamental main group chemistry. The stability of Group 14 metallylenes (R₂E) enhances with increasing the principal quantum number (E=Si<Ge<Sn<Pb) owing to the so-called inert-pair effect. However, the increasing size difference between carbon and a heavier Group 14 element (Si<Ge<Sn<Pb) leads to inefficient π_E–π_C interactions and poor delocalization of π-electrons. Combining both aromatic and metallylene features in the same molecule, for instance the heavier analogues of benzene-1,4-diide (C₆H₄)^2– that results by the two-fold 1,4-deprotonation of benzene, remained however an uncharted research area. The successful isolation of such compounds calls for innovative design-concepts for the development of suitable ligand scaffolds. The aim of this Concept Article is to showcase the recent developments in the field and to provide the reader an overview on the structure and properties of a new class of heavier aromatics with two-coordinated Group 14 elements in a formally +1 oxidation state.