Olefin metathesis is arguably the most versatile catalytic route yet developed for the assembly of carbon-carbon bonds. Metathesis methodologies are attractive from both synthetic and ecological standpoints, because they employ unactivated double bonds. This reduces the total number of synthetic steps, and the associated generation of chemical wastes. The drive to deploy olefin metathesis in highly demanding contexts, including materials science, chemical biology and pharmaceutical manufacturing, puts severe pressure on catalyst lifetime and productivity.<br/>The first in-depth mechanistic examination of decomposition pathways that underlie the success and failure for leading NHC catalysts, in comparison to a new family of catalysts stabilized by cyclic (alkyl)(amino) carbene (CAAC) ligands will be presented. Recently, CAAC catalysts have attracted much attention for their breakthrough productivities in challenging metathesis transformations. The remarkable productivity of the CAAC catalysts is shown to originate from their resistance to decomposition of the key metallacyclobutane intermediate via b-elimination. Importantly, however, they are more susceptible to bimolecular decomposition. The underlying reason for such behavior was traced to the strong trans effect of the CAAC relative to NHC ligands. This insight significantly advances our understanding of the fundamental properties governing both productivity and decomposition.<br/>The knowledge acquired on catalyst decomposition has allowed us to develop two new catalysts. In the first of these complexes, an <i>o</i>-dianiline ligand is employed to stabilize the precatalyst. This flexible, H-bonding chelate serves the further purpose of accelerating macrocyclization of flexible dienes that bear polar functionalities. Since its publication, this catalyst has been adopted in pharmaceutical science for the production of DNA-encoded chemical libraries in aqueous media. The other example consists of a dimer bearing bulky Ru-indenylidene centers, in which a dative bond from a bridging chloride affords the fifth ligand essential to stabilize the precatalyst.

Advances in olefin metathesis: From catalyst decomposition to redesign

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.