Synthesis of the Unknown Indeno1,2-afluorene Regioisomer: Crystallographic Characterization of Its Dianion

摘要

Of the five possible indenofluorene regioisomers, examples of a fully conjugated indeno1,2-afluorene scaffold have so far remained elusive. This work reports the preparation and characterization of 7,12-dimesitylindeno1,2-afluorene 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 indeno1,2-afluorene 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 indeno1,2-afluorene hydrocarbon core.