Aromatic Dicupra[10]annulenes

Metal-containing aromatic systems (metalla-aromatics) are unique and important both experimentally and theoretically. Among metalla-aromatics, six-membered metallabenzenes and metallabenzynes have attracted much attention in recent years. However, reports on their superior homologues are rare. In this work, the first series of aromatic dicupra­[10]­annulenes were isolated from the reaction of dilithio reagents and copper salts. Single-crystal X-ray structural analysis revealed dicupra­[10]­annulenes with averaged bond lengths. 7Li NMR spectra and theoretical calculations revealed considerable aromatic character. XPS data suggested that the oxidation state of Cu atom in dicupra[10]­annulenes was more likely to be Cu­(I), indicating that the dilithio moieties in dicupra[10]­annulenes participated as noninnocent ligands. This work demonstrates a novel approach to construct macrocyclic metalla-aromatics.