2-Pyridylnitrene-1,3-diazacyclohepta-1,2,4,6-tetraene rearrangements in the trifluoromethyl-2-pyridyl azide series

Photolysis of Ar matrix isolated trifluoromethyl-substituted 2-pyridyl azides/tetrazolo[1,5-a]pyridines at 12-18 K causes rapid and mostly clean conversion to the corresponding 1,3-diazacyclohepta-1,2,4,6-tetraenes (4D, 5D, 5,6D, and 4,6D) absorbing near 2000 cm(-1) in the IR. In the latter case, the intermediate 3,5-bis(trifluoromethyl)-2-pyridylnitrene (4,6N) was observed by both ESR and IR spectroscopy and converted to the diazacycloheptatetraene 4,6D in the course of 90 min of UV irradiation. The 2-pyridylnitrenes were generally observable by ESR spectroscopy (\D/hc\similar to 1.05-1.10; \E/hc\similar to 0.0 cm(-1)) following both photochemical and thermal (FVP) generation from the 2-azidopyridines. Irradiation of the Ar matrix isolated mixtures of nitrenes and diazacycloheptatetraenes also caused development of weak carbene transitions (\D/hc\similar to 0.40-0.45;\E/hc\similar to 0.006 cm(-1)) in the ESR spectra.