Generation, Reactions, Direct Observation, and Kinetics of Decafluorodiphenylcarbene

Article abstract of DOI:10.1021/jo00077a040

Bis(pentafluorophenyl)diazomethane (1a) was prepared, and reactivities of perfluorodiphenylcarbene (2a) generated by photolysis of 1a were investigated not only in terms of product analysis but also by using matrix isolation spectroscopy as well as laser flash photolysis techniques.Product distributions observed in the reactions of 2a in benzene, cyclohexane, and trans-1,2-dichloroethylene suggested that 2a reacted with those substrates with moderate reactivities toward carbene mostly in its singlet state presumably owing to the increased electrophilicity induced by fluorine substituents while the reaction with the alkane C-H bonds in concerted fashion was retarded partly due to steric effect in the singlet state which thus decayed to the triplet states that underwent predominantly H atom abstraction forming tetraarylethane.Photolysis of 1a in Ar matrix at 10 K produced 2a which was observed by IR and UV and shown to react with doped O2 to produce ultimately perfluorobenzoate by way of the carbonyl oxide and dioxirane, both intermediates being characterized by IR and UV/vis spectroscopy.Laser flash photolysis of 1a in acetonitrile solution produced a transient absorption (λ = 320 nm) due to bis(pentafluorophenyl)methyl radical (14a) obviously produced by H atom abstraction of the triplet 2a, which was trapped by oxygen to generate the carbonyl oxide (11a) showing its absorption maximum at 400 nm (τ = 5 ms) and also by 1,4-cyclohexadiene to form the methyl radical (14a) with the rate constant of 1.1E7 M^-1 s^-1.The lifetime of the triplet 2a was estimated to be ca. 1 μs.