Matrix Isolation Studies of Photochemical and Thermal Reactions of 3- and 5-Membered Cyclic Hydrocarbons with CrCl₂O₂

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to characterize the products of the photochemical and thermal reactions of cyclopentadiene, cyclopentene, cyclopentane, and cyclopropane with CrCl₂O₂. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, product bands were observed following irradiation with light of λ > 300 nm. The irradiation was shown to lead to oxygen atom transfer to the five-membered rings, forming complexes between cyclic alcohol derivatives and CrCl₂O. For the cyclopentadiene and cyclopentene systems, complexes between cyclic ketone derivatives and CrCl₂O were also observed. For cyclopropane, a ring-opening oxidation reaction followed by fragmentation was observed for the first time, forming the H₂COCrCl₂O complex and C₂H₄. In the room temperature thermal (merged jet) reactions between CrCl₂O₂ and cyclopentadiene, cyclopent-3-enone was observed. At the higher temperatures, 150 and 200 °C, 1,3-cyclopentanedione was also observed as well. No product bands were detected in the merged jet experiments for the other three systems. These conclusions were supported by isotopic labeling (²H) and by B3LYP/6-311G++(d,2p) density functional calculations.