Reactions of carbenes in low-temperature matrices: Direct IR spectroscopic observation of (1+2)-cycloaddition of cyclopentadienylidene to ethylene

1. Cyclopentadienylidene (I) in the total absence of its dimer, fulvalene (IV), was selectively obtained by UV photolysis (λ > 300 nm) of diazocyclopentadiene in an argon matrix with addition of 10–15% N2O. 2. Direct IR spectroscopic observation of the reaction of the carbene with an organic molecule on the example of the reaction of (1+2)-cycloaddition of triplet (I) to ethylene in an Ar matrix at 40–45 K was conducted for the first time. 3. Dimerization of triplet (I) into (IV) is observed in the absence of C2H4 in the Ar matrix when the temperature is increased from 12 to 40–45 K.