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The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation

The oxidative addition of Pd to Si–H bonds is a crucial step in a variety of catalytic applications, and many aspects of this reaction are poorly understood. One important yet underexplored aspect is the electronic effect of silane substituents on reactivity. Herein we describe a systematic investig...

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Autores principales: Hurst, Michael R., Zakharov, Lev N., Cook, Amanda K.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Royal Society of Chemistry 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8513848/
https://www.ncbi.nlm.nih.gov/pubmed/34745535
http://dx.doi.org/10.1039/d1sc04419b
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author Hurst, Michael R.
Zakharov, Lev N.
Cook, Amanda K.
author_facet Hurst, Michael R.
Zakharov, Lev N.
Cook, Amanda K.
author_sort Hurst, Michael R.
collection PubMed
description The oxidative addition of Pd to Si–H bonds is a crucial step in a variety of catalytic applications, and many aspects of this reaction are poorly understood. One important yet underexplored aspect is the electronic effect of silane substituents on reactivity. Herein we describe a systematic investigation of the formation of silyl palladium hydride complexes as a function of silane identity, focusing on electronic influence of the silanes. Using [(μ-dcpe)Pd](2) (dcpe = dicyclohexyl(phosphino)ethane) and tertiary silanes, data show that equilibrium strongly favours products formed from electron-deficient silanes, and is fully dynamic with respect to both temperature and product distribution. A notable kinetic isotope effect (KIE) of 1.21 is observed with H/DSiPhMe(2) at 233 K, and the reaction is shown to be 0.5(th) order in [(μ-dcpe)Pd](2) and 1(st) order in silane. Formed complexes exhibit temperature-dependent intramolecular H/Si ligand exchange on the NMR timescale, allowing determination of the energetic barrier to reversible oxidative addition. Taken together, these results give unique insight into the individual steps of oxidative addition and suggest the initial formation of a σ-complex intermediate to be rate-limiting. The insight gained from these mechanistic studies was applied to hydrosilylation of alkynes, which shows parallel trends in the effect of the silanes' substituents. Importantly, this work highlights the relevance of in-depth mechanistic studies of fundamental steps to catalysis.
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spelling pubmed-85138482021-11-04 The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation Hurst, Michael R. Zakharov, Lev N. Cook, Amanda K. Chem Sci Chemistry The oxidative addition of Pd to Si–H bonds is a crucial step in a variety of catalytic applications, and many aspects of this reaction are poorly understood. One important yet underexplored aspect is the electronic effect of silane substituents on reactivity. Herein we describe a systematic investigation of the formation of silyl palladium hydride complexes as a function of silane identity, focusing on electronic influence of the silanes. Using [(μ-dcpe)Pd](2) (dcpe = dicyclohexyl(phosphino)ethane) and tertiary silanes, data show that equilibrium strongly favours products formed from electron-deficient silanes, and is fully dynamic with respect to both temperature and product distribution. A notable kinetic isotope effect (KIE) of 1.21 is observed with H/DSiPhMe(2) at 233 K, and the reaction is shown to be 0.5(th) order in [(μ-dcpe)Pd](2) and 1(st) order in silane. Formed complexes exhibit temperature-dependent intramolecular H/Si ligand exchange on the NMR timescale, allowing determination of the energetic barrier to reversible oxidative addition. Taken together, these results give unique insight into the individual steps of oxidative addition and suggest the initial formation of a σ-complex intermediate to be rate-limiting. The insight gained from these mechanistic studies was applied to hydrosilylation of alkynes, which shows parallel trends in the effect of the silanes' substituents. Importantly, this work highlights the relevance of in-depth mechanistic studies of fundamental steps to catalysis. The Royal Society of Chemistry 2021-09-14 /pmc/articles/PMC8513848/ /pubmed/34745535 http://dx.doi.org/10.1039/d1sc04419b Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/
spellingShingle Chemistry
Hurst, Michael R.
Zakharov, Lev N.
Cook, Amanda K.
The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title_full The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title_fullStr The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title_full_unstemmed The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title_short The mechanism of oxidative addition of Pd(0) to Si–H bonds: electronic effects, reaction mechanism, and hydrosilylation
title_sort mechanism of oxidative addition of pd(0) to si–h bonds: electronic effects, reaction mechanism, and hydrosilylation
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8513848/
https://www.ncbi.nlm.nih.gov/pubmed/34745535
http://dx.doi.org/10.1039/d1sc04419b
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