Merging central and axial chirality in Cyclic(alkyl)(amino)carbenes: The keystone for high enantioselectivities in Ru-catalyzed asymmetric olefin metathesis

A series of 38 chiral ruthenium complexes containing cyclic(alkyl)(amino)carbene (CAAC) ligands with axial C-N chirality have been developed. By merging axial and central chirality, very high enantioselectivity (up to >99% ee) as well as good to high E-selectivity (up to 98%) were achieved in the asymmetric ring-opening cross metathesis (AROCM) of various norbornene and cyclopropene derivatives. Furthermore, these catalysts are efficient in the challenging asymmetric ring-closing ene-yne metathesis (ARCEYM), providing valuable enantioenriched building blocks (up to 90% ee). Mechanistic insights from density functional theory (DFT) calculations highlight the crucial role of axial chirality in CAAC ligands in governing both enantio- and diastereoselectivity in the metathesis reaction.