Diboron-Incorporated Indenofluorene: Isolation of Crystalline Neutral and Reduced States of 6,12-Diboraindeno[1,2-]fluorene.

The synthesis and redox transformations of 6,12-diboraindeno[1,2-]fluorene (DBIF)─a pentacyclic π-system with diboron incorporation─are reported. In notable contrast to the all-hydrocarbon indenofluorenes, a ligand coordination and reduction strategy allows tuning of the electronic structure across four redox states. Accordingly, we introduce an 18π e neutral DBIF, a 20π e diradical, a 21π e radical anion, and a 22π e dianion, all of which have been isolated and structurally authenticated. The diradicals exhibit diradical character of up to 77% and possess open-shell singlet ground states with thermally accessible triplet states.