Cargando…

The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition

Ruthenium–cyclic(alkyl)(amino)carbene (CAAC) catalysts, used at ppm levels, can enable dramatically higher productivities in olefin metathesis than their N-heterocyclic carbene (NHC) predecessors. A key reason is the reduced susceptibility of the metallacyclobutane (MCB) intermediate to decompositio...

Descripción completa

Detalles Bibliográficos
Autores principales: Occhipinti, Giovanni, Nascimento, Daniel L., Foscato, Marco, Fogg, Deryn E., Jensen, Vidar R.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9093171/
https://www.ncbi.nlm.nih.gov/pubmed/35655574
http://dx.doi.org/10.1039/d2sc00855f
_version_ 1784705277965107200
author Occhipinti, Giovanni
Nascimento, Daniel L.
Foscato, Marco
Fogg, Deryn E.
Jensen, Vidar R.
author_facet Occhipinti, Giovanni
Nascimento, Daniel L.
Foscato, Marco
Fogg, Deryn E.
Jensen, Vidar R.
author_sort Occhipinti, Giovanni
collection PubMed
description Ruthenium–cyclic(alkyl)(amino)carbene (CAAC) catalysts, used at ppm levels, can enable dramatically higher productivities in olefin metathesis than their N-heterocyclic carbene (NHC) predecessors. A key reason is the reduced susceptibility of the metallacyclobutane (MCB) intermediate to decomposition via β-H elimination. The factors responsible for promoting or inhibiting β-H elimination are explored via density functional theory (DFT) calculations, in metathesis of ethylene or styrene (a representative 1-olefin) by Ru–CAAC and Ru–NHC catalysts. Natural bond orbital analysis of the frontier orbitals confirms the greater strength of the orbital interactions for the CAAC species, and the consequent increase in the carbene trans influence and trans effect. The higher trans effect of the CAAC ligands inhibits β-H elimination by destabilizing the transition state (TS) for decomposition, in which an agostic MCB C(β)–H bond is positioned trans to the carbene. Unproductive cycling with ethylene is also curbed, because ethylene is trans to the carbene ligand in the square pyramidal TS for ethylene metathesis. In contrast, metathesis of styrene proceeds via a ‘late’ TS with approximately trigonal bipyramidal geometry, in which carbene trans effects are reduced. Importantly, however, the positive impact of a strong trans-effect ligand in limiting β-H elimination is offset by its potent accelerating effect on bimolecular coupling, a major competing means of catalyst decomposition. These two decomposition pathways, known for decades to limit productivity in olefin metathesis, are revealed as distinct, antinomic, responses to a single underlying phenomenon. Reconciling these opposing effects emerges as a clear priority for design of robust, high-performing catalysts.
format Online
Article
Text
id pubmed-9093171
institution National Center for Biotechnology Information
language English
publishDate 2022
publisher The Royal Society of Chemistry
record_format MEDLINE/PubMed
spelling pubmed-90931712022-06-01 The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition Occhipinti, Giovanni Nascimento, Daniel L. Foscato, Marco Fogg, Deryn E. Jensen, Vidar R. Chem Sci Chemistry Ruthenium–cyclic(alkyl)(amino)carbene (CAAC) catalysts, used at ppm levels, can enable dramatically higher productivities in olefin metathesis than their N-heterocyclic carbene (NHC) predecessors. A key reason is the reduced susceptibility of the metallacyclobutane (MCB) intermediate to decomposition via β-H elimination. The factors responsible for promoting or inhibiting β-H elimination are explored via density functional theory (DFT) calculations, in metathesis of ethylene or styrene (a representative 1-olefin) by Ru–CAAC and Ru–NHC catalysts. Natural bond orbital analysis of the frontier orbitals confirms the greater strength of the orbital interactions for the CAAC species, and the consequent increase in the carbene trans influence and trans effect. The higher trans effect of the CAAC ligands inhibits β-H elimination by destabilizing the transition state (TS) for decomposition, in which an agostic MCB C(β)–H bond is positioned trans to the carbene. Unproductive cycling with ethylene is also curbed, because ethylene is trans to the carbene ligand in the square pyramidal TS for ethylene metathesis. In contrast, metathesis of styrene proceeds via a ‘late’ TS with approximately trigonal bipyramidal geometry, in which carbene trans effects are reduced. Importantly, however, the positive impact of a strong trans-effect ligand in limiting β-H elimination is offset by its potent accelerating effect on bimolecular coupling, a major competing means of catalyst decomposition. These two decomposition pathways, known for decades to limit productivity in olefin metathesis, are revealed as distinct, antinomic, responses to a single underlying phenomenon. Reconciling these opposing effects emerges as a clear priority for design of robust, high-performing catalysts. The Royal Society of Chemistry 2022-03-22 /pmc/articles/PMC9093171/ /pubmed/35655574 http://dx.doi.org/10.1039/d2sc00855f Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by/3.0/
spellingShingle Chemistry
Occhipinti, Giovanni
Nascimento, Daniel L.
Foscato, Marco
Fogg, Deryn E.
Jensen, Vidar R.
The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title_full The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title_fullStr The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title_full_unstemmed The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title_short The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
title_sort janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9093171/
https://www.ncbi.nlm.nih.gov/pubmed/35655574
http://dx.doi.org/10.1039/d2sc00855f
work_keys_str_mv AT occhipintigiovanni thejanusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT nascimentodaniell thejanusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT foscatomarco thejanusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT foggderyne thejanusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT jensenvidarr thejanusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT occhipintigiovanni janusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT nascimentodaniell janusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT foscatomarco janusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT foggderyne janusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition
AT jensenvidarr janusfaceofhightranseffectcarbenesinolefinmetathesisgatewaytobothproductivityanddecomposition