A crystalline radical cation derived from Thiele's hydrocarbon with redox range beyond 1 V

Organic molecules that can access various redox states have potential applications in electronics, batteries, catalysis, among others. Here the authors report the preparation of an unsymmetrical organoboron analogue of Thiele's hydrocarbon and study its one- and two-electron oxidation reactions; remarkably, the radical cation is stable over a redox range of > 1 V and can also be isolated. Thiele's hydrocarbon occupies a central role as an open-shell platform for new organic materials, however little is known about its redox behaviour. While recent synthetic approaches involving symmetrical carbene substitution of the CPh2 termini yield isolable neutral/dicationic analogues, the intervening radical cations are much more difficult to isolate, due to narrow compatible redox ranges (typically < 0.25 V). Here we show that a hybrid BN/carbene approach allows access to an unsymmetrical analogue of Thiele's hydrocarbon 1, and that this strategy confers markedly enhanced stability on the radical cation. 1(center dot+) is stable across an exceptionally wide redox range (> 1 V), permitting its isolation in crystalline form. Further single-electron oxidation affords borenium dication 1(2+), thereby establishing an organoboron redox system fully characterized in all three redox states. We perceive that this strategy can be extended to other transient organic radicals to widen their redox stability window and facilitate their isolation.

Automated summary

The authors prepared an unsymmetrical organoboron analogue of Thiele's hydrocarbon and studied its oxidation reactions, revealing that the radical cation is stable over a redox range of > 1 V and can be isolated. This strategy not only broadens the redox stability window of the compound but also has the potential to be extended to other transient organic radicals.