Olefin isomerization by iridium pincer catalysts. experimental evidence for an η 3-allyl pathway and an unconventional mechanism predicted by DFT calculations

Soumik Biswas, Zheng Huang, Yuriy Choliy, David Y. Wang, Maurice Brookhart, Karsten Krogh-Jespersen, Alan S Goldman

Research output: Contribution to journalArticle

68 Citations (Scopus)

Abstract

The isomerization of olefins by complexes of the pincer-ligated iridium species ( tBuPCP)Ir ( tBuPCP = κ 3-C 6H 3-2,6-(CH 2P tBu 2) 2) and ( tBuPOCOP)Ir ( tBuPOCOP = κ 3-C 6H 3-2,6-(OP tBu 2) 2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH 2, are known to hydrogenate olefins via initial Ir-H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for olefin isomerization (the "hydride addition pathway"); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η 2-olefin) species undergo isomerization via the formation of (pincer)Ir(η 3-allyl)(H) intermediates; one example of such a species, ( tBuPOCOP) Ir(η 3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to ( tBuPOCOP)Ir(η 2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η 2-olefin complex to the η 3-allyl hydride takes place via initial dissociation of the Ir-olefin π-bond to give a σ-complex of the allylic C-H bond; this intermediate then undergoes C-H bond oxidative cleavage to give an iridium η 1-allyl hydride which "closes" to give the η 3-allyl hydride. Subsequently, the η 3-allyl group "opens" in the opposite sense to give a new η 1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C-H elimination and π-coordination to give a coordinated olefin that has undergone double-bond migration.

Original languageEnglish
Pages (from-to)13276-13295
Number of pages20
JournalJournal of the American Chemical Society
Volume134
Issue number32
DOIs
Publication statusPublished - Aug 15 2012

Fingerprint

Iridium
Alkenes
Isomerization
Discrete Fourier transforms
Olefins
Catalysts
Hydrides
Propylene
Kinetics

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Olefin isomerization by iridium pincer catalysts. experimental evidence for an η 3-allyl pathway and an unconventional mechanism predicted by DFT calculations. / Biswas, Soumik; Huang, Zheng; Choliy, Yuriy; Wang, David Y.; Brookhart, Maurice; Krogh-Jespersen, Karsten; Goldman, Alan S.

In: Journal of the American Chemical Society, Vol. 134, No. 32, 15.08.2012, p. 13276-13295.

Research output: Contribution to journalArticle

Biswas, Soumik ; Huang, Zheng ; Choliy, Yuriy ; Wang, David Y. ; Brookhart, Maurice ; Krogh-Jespersen, Karsten ; Goldman, Alan S. / Olefin isomerization by iridium pincer catalysts. experimental evidence for an η 3-allyl pathway and an unconventional mechanism predicted by DFT calculations. In: Journal of the American Chemical Society. 2012 ; Vol. 134, No. 32. pp. 13276-13295.
@article{80fa5488293c4c2890d4001624308859,
title = "Olefin isomerization by iridium pincer catalysts. experimental evidence for an η 3-allyl pathway and an unconventional mechanism predicted by DFT calculations",
abstract = "The isomerization of olefins by complexes of the pincer-ligated iridium species ( tBuPCP)Ir ( tBuPCP = κ 3-C 6H 3-2,6-(CH 2P tBu 2) 2) and ( tBuPOCOP)Ir ( tBuPOCOP = κ 3-C 6H 3-2,6-(OP tBu 2) 2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH 2, are known to hydrogenate olefins via initial Ir-H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for olefin isomerization (the {"}hydride addition pathway{"}); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η 2-olefin) species undergo isomerization via the formation of (pincer)Ir(η 3-allyl)(H) intermediates; one example of such a species, ( tBuPOCOP) Ir(η 3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to ( tBuPOCOP)Ir(η 2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η 2-olefin complex to the η 3-allyl hydride takes place via initial dissociation of the Ir-olefin π-bond to give a σ-complex of the allylic C-H bond; this intermediate then undergoes C-H bond oxidative cleavage to give an iridium η 1-allyl hydride which {"}closes{"} to give the η 3-allyl hydride. Subsequently, the η 3-allyl group {"}opens{"} in the opposite sense to give a new η 1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C-H elimination and π-coordination to give a coordinated olefin that has undergone double-bond migration.",
author = "Soumik Biswas and Zheng Huang and Yuriy Choliy and Wang, {David Y.} and Maurice Brookhart and Karsten Krogh-Jespersen and Goldman, {Alan S}",
year = "2012",
month = "8",
day = "15",
doi = "10.1021/ja301464c",
language = "English",
volume = "134",
pages = "13276--13295",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "32",

}

TY - JOUR

T1 - Olefin isomerization by iridium pincer catalysts. experimental evidence for an η 3-allyl pathway and an unconventional mechanism predicted by DFT calculations

AU - Biswas, Soumik

AU - Huang, Zheng

AU - Choliy, Yuriy

AU - Wang, David Y.

AU - Brookhart, Maurice

AU - Krogh-Jespersen, Karsten

AU - Goldman, Alan S

PY - 2012/8/15

Y1 - 2012/8/15

N2 - The isomerization of olefins by complexes of the pincer-ligated iridium species ( tBuPCP)Ir ( tBuPCP = κ 3-C 6H 3-2,6-(CH 2P tBu 2) 2) and ( tBuPOCOP)Ir ( tBuPOCOP = κ 3-C 6H 3-2,6-(OP tBu 2) 2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH 2, are known to hydrogenate olefins via initial Ir-H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for olefin isomerization (the "hydride addition pathway"); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η 2-olefin) species undergo isomerization via the formation of (pincer)Ir(η 3-allyl)(H) intermediates; one example of such a species, ( tBuPOCOP) Ir(η 3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to ( tBuPOCOP)Ir(η 2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η 2-olefin complex to the η 3-allyl hydride takes place via initial dissociation of the Ir-olefin π-bond to give a σ-complex of the allylic C-H bond; this intermediate then undergoes C-H bond oxidative cleavage to give an iridium η 1-allyl hydride which "closes" to give the η 3-allyl hydride. Subsequently, the η 3-allyl group "opens" in the opposite sense to give a new η 1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C-H elimination and π-coordination to give a coordinated olefin that has undergone double-bond migration.

AB - The isomerization of olefins by complexes of the pincer-ligated iridium species ( tBuPCP)Ir ( tBuPCP = κ 3-C 6H 3-2,6-(CH 2P tBu 2) 2) and ( tBuPOCOP)Ir ( tBuPOCOP = κ 3-C 6H 3-2,6-(OP tBu 2) 2) has been investigated by computational and experimental methods. The corresponding dihydrides, (pincer)IrH 2, are known to hydrogenate olefins via initial Ir-H addition across the double bond. Such an addition is also the initial step in the mechanism most widely proposed for olefin isomerization (the "hydride addition pathway"); however, the results of kinetics experiments and DFT calculations (using both M06 and PBE functionals) indicate that this is not the operative pathway for isomerization in this case. Instead, (pincer)Ir(η 2-olefin) species undergo isomerization via the formation of (pincer)Ir(η 3-allyl)(H) intermediates; one example of such a species, ( tBuPOCOP) Ir(η 3-propenyl)(H), was independently generated, spectroscopically characterized, and observed to convert to ( tBuPOCOP)Ir(η 2-propene). Surprisingly, the DFT calculations indicate that the conversion of the η 2-olefin complex to the η 3-allyl hydride takes place via initial dissociation of the Ir-olefin π-bond to give a σ-complex of the allylic C-H bond; this intermediate then undergoes C-H bond oxidative cleavage to give an iridium η 1-allyl hydride which "closes" to give the η 3-allyl hydride. Subsequently, the η 3-allyl group "opens" in the opposite sense to give a new η 1-allyl (thus completing what is formally a 1,3 shift of Ir), which undergoes C-H elimination and π-coordination to give a coordinated olefin that has undergone double-bond migration.

UR - http://www.scopus.com/inward/record.url?scp=84865130989&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84865130989&partnerID=8YFLogxK

U2 - 10.1021/ja301464c

DO - 10.1021/ja301464c

M3 - Article

C2 - 22765770

AN - SCOPUS:84865130989

VL - 134

SP - 13276

EP - 13295

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 32

ER -