Matrix isolation and spectroscopic characterization of perfluorinated ortho- and meta-benzyne

The matrix isolation and spectroscopic characterization of two CBF, isomers , the perfluorinated o-benzyne 4 and the m-benzyne 5, is reported. UV photo lysis of tetrafluorophthalic anhydride 6 in solid argon at 10 K results in the formation of CO, CO2, and 1,2 didehydro-3,4,5,6-tetrafluorobenzene (4) in a clean reaction. On subsequent 350 nm irradiation 4 is carbonylated to give the cyclopropenone 7. 1,3-Didehydro-2,4,5,6-tetrafluorobenzene (5) was synthesized by UV irradiation of 1,3diiodo-2,4,5,6-tetrafluorobenzene (8) via 2,3,4,6-tetrafluoro-5-iodophenylradical 9, Photolysis of 8 in solid neo n at 3 K produces good yields of both radical 9 and benzyne 5, while in arg on at 10 K no reaction is observed. Thus, the photo-chemistry in neon at ex tremely low temperature markedly differs from the photochemistry in argon. The formation of 5 from 8 via 9 is reversible, and annealing the neon matri x at 8 K leads back to the starting material 8. The benzynes 4 and 5 and th e radical 9 were characterized by comparison of their matrix IR spectra wit h density functional theory (DFT) calculations.