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The synthesis and redox transformations of 6,12-diboraindeno1,2- b 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.
Tra et al. (Wed,) studied this question.