Photoinduced electron transfer reactions: Nitrogen-oxygen bond cleavage in reduced N-(aryloxy)pyridinium and N,N′-dialkoxy-4,4′-bipyridinium salts

Article abstract of DOI:10.1021/ja00050a010

N-(Aryloxy)pyridinium cations and N,N-dialkoxy-4,4′-bipyridinium dications form charge-transfer complexes with neutral hydrocarbons. Irradiation of these charge-transfer complexes leads to the cleavage of the nitrogen-oxygen bond and the formation of an aryloxy radical in the first case, but no reaction is observed for the second. In contrast, electron transfer to the dialkoxybipyridinium cation from the triplet state of 9-acetylanthracene leads to nitrogen-oxygen bond cleavage and the formation of an alkoxy radical. The rate constants for nitrogen-oxygen bond cleavage (k_BC) in the reduced pyridinium salts were estimated by time-resolved laser spectroscopy. For N-(4-cyanophenoxy)pyridinium tetrafluoroborate, k_BC> 10¹¹ s^-1, and for N,N-diethoxy-4,4′-bipyridinium (bis)hexafluorophosphate), k_BC = 1.4 × 10⁴ s^-1. The effects of structure on the dynamics of the excited charge-transfer complexes and on k_BC are discussed.