Benzdiynes (1,2,4,5-Tetradehydrobenzenes): Direct Observation by Wavelength-Selective Photolyses of Benzenetetracarboxylic Dianhydrides in Low-Temperature Nitrogen Matrixes

Abstract

Toward direct observation of benzdiynes, we investigated the wavelength-selective photolyses of five kinds of benzenetetracarboxylic dianhydride derivatives in nitrogen matrixes at 13 K. In the first step of the photolyses, all dianhydrides were converted into benzynedicarboxylic anhydrides with loss of CO and CO2 upon irradiation at 308 nm. In the second step, the benzyne intermediates were photolyzed at 266 nm. In these photolyses, the generation of two kinds of benzdiynes, 3,6-difluoro-1,4-benzdiyne and 3,6-bis(trifluoromethyl)-1,4-benzdiyne, was confirmed by good correspondence between observed and calculated IR spectra. These benzdiynes were converted into the corresponding hexatriynes upon further irradiation at 266 nm. Benzdiynes were not observed in the photolyses of the other three dianhydrides: only hexatriynes were observed as major photoproducts. These results suggested that benzdiynes were generated first and then converted into hexatriynes and that the efficiency of the decomposition of benzdiynes depended on the substituents. The dynamics of the generation and decomposition of benzdiynes in the matrixes was analyzed by using a successive reaction scheme.