Synthesis of the Unknown Indeno[1,2‐<i>a</i>]fluorene Regioisomer: Crystallographic Characterization of Its Dianion

Abstract

Abstract Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno[1,2‐ a ]fluorene scaffold have so far remained elusive. This work reports the preparation and characterization of 7,12‐dimesitylindeno[1,2‐ a ]fluorene as a highly reactive species. Experimental and computational data support the notion of a molecule with pronounced diradical character that exists in a triplet ground state. As such, both NICS and ACID calculations suggest that the indeno[1,2‐ a ]fluorene scaffold is weakly Baird aromatic. Reduction of the unstable red solid with Cs metal produces the dianion of the title compound, from which single crystals could be obtained and X‐ray data acquired, thus fully corroborating the proposed indeno[1,2‐ a ]fluorene hydrocarbon core.