Photochemical generation and characterization of the 5-endo-10,11-dihydrodibenzoazepine nitrenium ion.

A photochemical precursor to the 5-endo-10,11-dihydroazepine nitrenium ion (1) was synthesized and used to characterize the intermediate by laser flash photolysis and stable product analysis. In addition, DFT calculations were carried out on the nitrenium ion. These results were compared with earlier studies on the diphenylnitrenium ion in order to ascertain the effect of the 2 carbon bridge on the reactions and properties of 1. It is shown that the geometric constraints provided by the bridging group (a) destabilize the triplet state of 1 relative to the singlet state (b) substantially increase the lifetime of 1 relative to Ph 2 N + by inhibiting the unimolecular cyclization pathway possible in the latter and (c) modestly increases the barrier for nucleophilic addition to the ring carbons.