Free difluoroethyne FCCF: isolation, some properties, and matrix IR spectra

Abstract

Difluoroethyne FCCF ( 1) is the last of the dihaloethyne molecules which, in spite of the continuing chemical and theoretical interest, could hitherto not be properly characterized. We have now synthesized and isolated pure 1 on a 50 mg scale by vacuum pyrolysis of perfluoro-1,2,3-triazene and characterized by 19F NMR, mass and IR spectra. 1 decomposes slowly at −196°C; in the gas phase at room temperature its half-life at ∼2 mbar is of the order of 15 minutes. The gas phase decomposition encompasses, in a first step, formation of a carbonaceous material and CF 2, which reacts with further C 2F 2 to form 3 different C 3F 4 isomers. In the condensed phase mainly C 2F 4 is formed. IR spectra of 1 in Ne and Ar matrices in the 200–5000 cm −1 range have been recorded. Beside the unambiguous detection of CF 2 as primary decomposition product they provide information on all vibrational levels ν 1 to ν 5 either directly (ν 2, ∑ + u, see figure, and ν 5, Π u) or by means of combination and overtone bands. ▪