4-Oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene - A highly electrophilic triplet carbene

The 4-oxocyclohexa-2,5-dienylidenes are an interesting class of highly elec trophilic carbenes. We investigated the reactivity of the 2,3,5,6-tetrafluo rinated and -tetrachlorinated derivatives 1b and 1c with small molecules un der conditions of matrix isolation. The reactions with molecular oxygen and with carbon monoxide produce the expected carbonyl O-oxides and ketenes, r espectively. As a result of the extreme electrophilicity of 1b and c both c arbenes insert with no or very small activation barriers into H-2 or the CH bonds of hydrocarbons. Obviously, spin restrictions for these formally spi n-forbidden reactions do not result in substantial thermal activation barri ers.