Charge-transfer activation of aromatic EDA complexes with N-nitrosopyridinium. Direct comparison with the N-nitropyridinium acceptor

The N-nitrosopyridinium cation (PyNO+) forms a series of intermolecular EDA complexes with aromatic hydrocarbons which show distinctive charge-transfer absorption bands in the visible region. Upon standing at room temperature, the EDA complexes in acetonitrile undergo a redox transformation into nitric oxide and oxidative pyridine adducts at the ipso positions of such electron-rich donors as 1,4-dimethylnaphthalene and durene—the latter of which has been structurally characterized by X-ray crystallography. Since the same adducts are formed when the EDA complexes (at low temperatures) are deliberately irradiated at their charge-transfer absorption bands, an electron-transfer mechanism is readily delineated for both the thermal and photochemical activation of the aromatic EDA complexes with PyNO+.