| Abstract
| - The photochemistry of 3-iodo-2,4,5,6-tetrafluorophenyl azide 8 and 3,5-diiodo-2,4,6-trifluorophenyl azide9 was studied by IR and EPR spectroscopy in cryogenic argon and neon matrices. Both compounds formthe corresponding nitrenes as primary photoproducts in photostationary equilibria with their azirine andketenimine isomers. In contrast to fluorinated phenylnitrenes, ring-opened products are obtained uponshort-wavelength irradiation of the iodine-containing systems, indicative of C−I bond cleavage in thenitrenes or didehydroazepines under these conditions. Neither 3-dehydrophenylnitrene 6 nor 3,5-didehydrophenylnitrene 7 could be detected directly. The structures of the acyclic photoproducts wereidentified by extensive comparison with DFT calculated spectra. Mechanistic aspects of the rearrangementsleading to the observed products and the electronic properties of the title intermediates are discussed onthe basis of DFT as well as high-level ab initio calculations. The computations indicate strong through-bond coupling of the exocyclic orbital in the meta position with the singly occupied in-plane nitreneorbital in the monoradical nitrenes. In contrast to the ortho or para isomers, this interaction results inlow-spin ground states for meta nitrene radicals and a weakening of the C1−C2 bond causing the kineticinstability of these species even under low-temperature conditions. 3,5-Didehydrophenylnitrenes, on theother hand, in which a strong C3−C5 interaction reduces coupling of the radical sites with the nitreneunit, might be accessible synthetic targets if the intermediate formation of labile monoradicals could becircumvented.
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