Kinetic Topochemical Effect on Methanol Insertion into Phenyl-α-ketocarbene

Abstract

The matrix isolation of methanol insertion has been performed into phenyl-α-ketocarbene (PKC) along with temperature decrease from the room temperature to the cryogenic temperature and the critical point of structure-spin inversion has been obtained by the kinetic results. The matrix isolation spectroscopic technique has been employed and the rate constants have been obtained by the laser flash photolysis and FT-IR and UV/ vis spectroscopic measurements. The results show that the singlet carbene reacts through a proton abstraction in the high temperature range, 254-312 K, whereas the non-Arrhenius behavior and abnormal temperature effect on the magnitude of the Hammett ρ indicates that the triplet carbene reaction occurs in the low temperature range, 77-154 K. The spin inversion was found to occur at about 254 K. A strong relationship exists between the spin state of the carbene and the geometry and reactivity of the carbene. It was found that the colder matrices of hexafluorobenzene and methanol are more rigid and permits a smaller range of motion for the PKC, and the reaction is controlled by topochemical inversion.