Lewis Acid-Mediated Radical Stabilization and Dynamic Covalent Bonding: Tunable, Reversible and Photocontrollable.

This work describes a strategy not only to isolate a dynamically stable radical with physical property tunability, but to efficiently regulate the radical dissociation with reversibility and photo controllability. The addition of Lewis acid B(C6 F5 )3 (BCF) into the solution of a radical σ-dimer (1-1) led to a stable radical (1⋅-2B), which has been characterized by EPR spectroscopy, UV/Vis spectroscopy and single crystal X-ray diffraction, in conjunction with theoretical calculation. The radical species is stabilized mainly by captodative effect, single electron transfer and steric effect. The absorption maximum of the radical can be tuned by using different Lewis acids. Dimer 1-1 can be achieved back by addition of a stronger base into the solution of 1⋅-2B, exhibiting a reversible process. By introducing a photo BCF generator, the dissociation of the dimer and the formation of the radical adduct become photocontrollable.