Kinetic and Theoretical Studies of the [3 + 2] Cycloadditions of Alkynyl Fischer Carbene Complexes with<i>N</i>-Alkyl Nitrones

Abstract

The 1,3-dipolar cycloadditions of alkynyl Fischer carbene complexes with nitrones to give 2,3-dihydroisoxazole carbene complexes were found to undergo first-order kinetics both for the nitrones and alkynyl carbene complexes. The effects of metals, substitutents of the nitrones and complexes, and solvents were studied. The rates increased with the more electron rich nitrones and less electron rich metal complexes. Ab initio theoretical calculations supported that the HOMO of nitrones and the LUMO of carbene complexes were the interacting frontier molecular orbitals. Only little dependence of solvent was observed, and therefore a concerted pathway is more likely.