Computational considerations on the mechanism and stereoselectivity in cyclopropanation reactions via iron-carbenes

Abstract

Iron-carbenes bearing heme or piano-stool groups as ancillary ligands are important catalyst for cyclopropanation via carbene transfer to olefins. The reaction mechanism operates through a concerted or a stepwise pathway. In most situations, the main product is the trans-cyclopropane, however, the cis-cyclopropane appears as the main product in some situations. We have performed DFT calculations to model the reaction mechanisms considering different spin states and different substituents for the two types of iron-carbenes above mentioned. Our results suggest that olefin cyclopropanation occurs mainly by the stepwise pathway, throughout a multi-state reactivity, or by a concerted pathway, depending on the catalyst. The origin of the diastereoselectivity is diverse, however, mainly related to the non-covalent interactions present in the transition structures of the main barrier in the mechanisms.