Reversible o-Dimerizations of Persistent Organic Radical Cations

摘要

C-C bond formation and cleavage are basic events in organic chemistry. The oxidative σ-dimerization of conjugated aromatic systems involving C—C coupling plays an essential role in organic syntheses, such as oxidative oligo-and polymerization. where a σ-dimeric dication is suggested as a key intermediate. Fast-scan cyclic voltammetry and NMR spectroscopic studies have suggested the existence of a doubly charged a-dimeric species in solution. Effenberger and co-workers succeeded in isolating a dimeric σ-complexed dication of 1,3,5-tripyrrolidinobenzene in 1969 and proved the existence of the σ-dimer in the solid state. More examples of dimeric complexes have been isolated subsequently. In the previously reported oxidative dimerizations, however, the radical cations have not been directly observed and well confirmed owing to their short lifetime. In fact, all of the dimerized structures of persistent radical cations of π-conjugated systems observed in the solid state are π-dimers.