Computational Mechanistic Studies on Enantioselective pybox−Ruthenium-Catalyzed Cyclopropanation Reactions

Abstract

The mechanism of the ruthenium(II)-catalyzed cyclopropanation reaction of olefins with diazo compounds has been extensively investigated for a medium-sized reaction model by means of DFT calculations. The starting ethylene complex of the dichloro[(E)-2-(methylimino)-N-(1E,2E)-2-(methyliminoethylidene)ethanamine]ruthenium(II) catalyst undergoes a ligand exchange with methyl diazoacetate to yield a reaction intermediate, which subsequently undergoes nitrogen extrusion to generate a ruthenium−carbene complex. The cyclopropanation step takes place through a direct carbene addition of the ruthenium carbene species to the olefin double bond to yield a catalyst-product complex, which can finally regenerate the starting complex. Stereochemical considerations on a “real-world” systemthe cyclopropanation reaction of styrene with methyl diazoacetate, catalyzed by a chiral pybox−ruthenium complexhave been investigated by means of full quantum-mechanical calculations on this reaction. The theoretical results show exce...