A theoretical study of the Heck reaction: N-heterocyclic carbene versus phosphine ligands

Ming Tsung Lee, Hon Man Lee, Ching Han Hu

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

The reaction mechanism of the Heck reaction has been studied using theoretical chemistry. Our main focus has been the comparison between phosphine ligands and N-heterocyclic carbenes (NHC) and between the normal C2-NHC versus the "abnormal" C5-NHC. Our overall free-energy landscape shows that oxidative addition involves a significant energy barrier, while the phosphine system is relatively favored. In the olefin insertion and β-hydride elimination steps, we considered both the neutral and ionic pathways. For the ionic pathway, the rate-determining step in addition to oxidative addition is olefin migration. For the neutral pathway, the second rate-determining step in addition to oxidative addition is also olefin insertion for NHC systems, while for the phosphine system the energy profile is much flatter. For the phosphine system, our result suggests that the neutral pathway is favored. Our study demonstrates that the catalytic capacity of Pd0L2 involving the "abnormal" C5-NHC ligand is comparable to the regular C2-NHC ligand. For the mechanisms examined in this study, there is no obvious advantage of using NHC ligands.

Original languageEnglish
Pages (from-to)1317-1324
Number of pages8
JournalOrganometallics
Volume26
Issue number6
DOIs
Publication statusPublished - 2007 Mar 12

Fingerprint

phosphine
carbenes
phosphines
Ligands
ligands
Alkenes
alkenes
insertion
Energy barriers
carbene
Hydrides
Free energy
hydrides
elimination

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

@article{48ee56758e0440b1a19eb92975ab0eca,
title = "A theoretical study of the Heck reaction: N-heterocyclic carbene versus phosphine ligands",
abstract = "The reaction mechanism of the Heck reaction has been studied using theoretical chemistry. Our main focus has been the comparison between phosphine ligands and N-heterocyclic carbenes (NHC) and between the normal C2-NHC versus the {"}abnormal{"} C5-NHC. Our overall free-energy landscape shows that oxidative addition involves a significant energy barrier, while the phosphine system is relatively favored. In the olefin insertion and β-hydride elimination steps, we considered both the neutral and ionic pathways. For the ionic pathway, the rate-determining step in addition to oxidative addition is olefin migration. For the neutral pathway, the second rate-determining step in addition to oxidative addition is also olefin insertion for NHC systems, while for the phosphine system the energy profile is much flatter. For the phosphine system, our result suggests that the neutral pathway is favored. Our study demonstrates that the catalytic capacity of Pd0L2 involving the {"}abnormal{"} C5-NHC ligand is comparable to the regular C2-NHC ligand. For the mechanisms examined in this study, there is no obvious advantage of using NHC ligands.",
author = "Lee, {Ming Tsung} and Lee, {Hon Man} and Hu, {Ching Han}",
year = "2007",
month = "3",
day = "12",
doi = "10.1021/om060651p",
language = "English",
volume = "26",
pages = "1317--1324",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "6",

}

A theoretical study of the Heck reaction : N-heterocyclic carbene versus phosphine ligands. / Lee, Ming Tsung; Lee, Hon Man; Hu, Ching Han.

In: Organometallics, Vol. 26, No. 6, 12.03.2007, p. 1317-1324.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A theoretical study of the Heck reaction

T2 - N-heterocyclic carbene versus phosphine ligands

AU - Lee, Ming Tsung

AU - Lee, Hon Man

AU - Hu, Ching Han

PY - 2007/3/12

Y1 - 2007/3/12

N2 - The reaction mechanism of the Heck reaction has been studied using theoretical chemistry. Our main focus has been the comparison between phosphine ligands and N-heterocyclic carbenes (NHC) and between the normal C2-NHC versus the "abnormal" C5-NHC. Our overall free-energy landscape shows that oxidative addition involves a significant energy barrier, while the phosphine system is relatively favored. In the olefin insertion and β-hydride elimination steps, we considered both the neutral and ionic pathways. For the ionic pathway, the rate-determining step in addition to oxidative addition is olefin migration. For the neutral pathway, the second rate-determining step in addition to oxidative addition is also olefin insertion for NHC systems, while for the phosphine system the energy profile is much flatter. For the phosphine system, our result suggests that the neutral pathway is favored. Our study demonstrates that the catalytic capacity of Pd0L2 involving the "abnormal" C5-NHC ligand is comparable to the regular C2-NHC ligand. For the mechanisms examined in this study, there is no obvious advantage of using NHC ligands.

AB - The reaction mechanism of the Heck reaction has been studied using theoretical chemistry. Our main focus has been the comparison between phosphine ligands and N-heterocyclic carbenes (NHC) and between the normal C2-NHC versus the "abnormal" C5-NHC. Our overall free-energy landscape shows that oxidative addition involves a significant energy barrier, while the phosphine system is relatively favored. In the olefin insertion and β-hydride elimination steps, we considered both the neutral and ionic pathways. For the ionic pathway, the rate-determining step in addition to oxidative addition is olefin migration. For the neutral pathway, the second rate-determining step in addition to oxidative addition is also olefin insertion for NHC systems, while for the phosphine system the energy profile is much flatter. For the phosphine system, our result suggests that the neutral pathway is favored. Our study demonstrates that the catalytic capacity of Pd0L2 involving the "abnormal" C5-NHC ligand is comparable to the regular C2-NHC ligand. For the mechanisms examined in this study, there is no obvious advantage of using NHC ligands.

UR - http://www.scopus.com/inward/record.url?scp=33947654846&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33947654846&partnerID=8YFLogxK

U2 - 10.1021/om060651p

DO - 10.1021/om060651p

M3 - Article

AN - SCOPUS:33947654846

VL - 26

SP - 1317

EP - 1324

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 6

ER -