Different Behavior of Nitrenes and Carbenes on Photolysis and Thermolysis:  Formation of Azirine, Ylidic Cumulene, and Cyclic Ketenimine and the Rearrangement of 6-Phenanthridylcarbene to 9-Phenanthrylnitrene

Flash vacuum thermolysis (FVT) of 9-azidophenanthrene 8, 6-(5-tetrazolyl)phenanthridine 18, and [1,2,3]triazolo[1,5-f]phenanthridine 19 yields 9-cyanofluorene 12 as the principal product and 4-cyanofluorene as a minor product. In all cases, when the product is condensed at or below 77 K, the seven-membered ring ketenimine 24 is detectable by IR spectroscopy (1932 cm^-1) up to 200 K. Photolysis of Ar matrix isolated 8 at λ = 308 or 313 nm generates at first the azirine 26, rapidly followed by the ylidic cumulene 27. The latter reverts to azirine 26 at λ > 405 nm, and the azirine reverts to the ylidic cumulene at 313 nm. Nitrene 9 is observed by ESR spectroscopy following FVT of either azide 8, tetrazole 18, or triazole 19 with Ar matrix isolation of the products. Nitrene 9 and carbene 21 are observed by ESR spectroscopy in the Ar matrix photolyses of azide 8 and triazole 19, respectively.