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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...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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The Royal Society of Chemistry
2022
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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 |
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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 |
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