Matrix Isolation of Perfluorinated p-Benzyne.

As the first isolated derivative of 1,4-didehydrobenzene, 1,4-didehydro-2,3,5,6-tetrafluorobenzene (1) was generated from 1,4-diiodotetrafluorobenzene (2) by photolysis at 254 nm in a neon matrix at 3 K. The 4-iodo-2,3,5,6-tetrafluorophenyl radical 3 is formed as an intermediate in this reaction. Both 1 and 3 were characterized by their IR spectra. Compound 1 is photolabile and undergoes a photochemical retro-Bergman reaction to 1,3,4,6-tetrafluorohex-3-ene-1,5-diyne (4) upon broad-band UV irradiation (260-320 nm).