Emerging metal-NHC as nanocatalysts: The kinetic stability of cyclopropyl substituted six-membered ring NHCs at DFT

A DFT study on the kinetic stability of two series of cyclopropyl substituted carbenes and N-heterocyclic carbenes (NHCs) constrained to the six-membered rings is reported. All carbenes studied have singlet electronic ground states. While the energy barrier for 1,2-C shift leading to ring opening of cyclopropyl carbene (results in the formation of cyclobutene) is rather small (4.1 kcal/mol), the presence of either second cyclopropyl and/or amino group (in NHCs) increases the energy barrier for this process. Unsaturation of rings by double bonds has small effects on the energy of this rearrangement. Hence, NHCs appear good candidates for increasing the kinetic stability and potent applications in the synthesis of corresponding metal nanocatalysts.