Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies

Sabuj Kundu, Jongwook Choi, David Y. Wang, Yuriy Choliy, Thomas J. Emge, Karsten Krogh-Jespersen, Alan S Goldman

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Abstract

A pincer-ligated iridium complex, (PCP)Ir (PCP = κ3-C 6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp3)-O bonds of methyl esters (CH3-O2CR′), methyl tosylate (CH 3-OTs), and certain electron-poor methyl aryl ethers (CH 3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H) [κ2-CH2OC(O)Me] which then affords (PCP-CH 2)Ir(H)(κ2-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ2-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

Original languageEnglish
Pages (from-to)5127-5143
Number of pages17
JournalJournal of the American Chemical Society
Volume135
Issue number13
DOIs
Publication statusPublished - Apr 3 2013

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Iridium
Ether
Ethers
Esters
Methyl Ethers
calcium ascorbate
Alkenes
Olefins
Thermolysis
Addition reactions
Discrete Fourier transforms
Hydrides

ASJC Scopus subject areas

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

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Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies. / Kundu, Sabuj; Choi, Jongwook; Wang, David Y.; Choliy, Yuriy; Emge, Thomas J.; Krogh-Jespersen, Karsten; Goldman, Alan S.

In: Journal of the American Chemical Society, Vol. 135, No. 13, 03.04.2013, p. 5127-5143.

Research output: Contribution to journalArticle

Kundu, Sabuj ; Choi, Jongwook ; Wang, David Y. ; Choliy, Yuriy ; Emge, Thomas J. ; Krogh-Jespersen, Karsten ; Goldman, Alan S. / Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies. In: Journal of the American Chemical Society. 2013 ; Vol. 135, No. 13. pp. 5127-5143.
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abstract = "A pincer-ligated iridium complex, (PCP)Ir (PCP = κ3-C 6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp3)-O bonds of methyl esters (CH3-O2CR′), methyl tosylate (CH 3-OTs), and certain electron-poor methyl aryl ethers (CH 3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H) [κ2-CH2OC(O)Me] which then affords (PCP-CH 2)Ir(H)(κ2-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ2-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.",
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T1 - Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies

AU - Kundu, Sabuj

AU - Choi, Jongwook

AU - Wang, David Y.

AU - Choliy, Yuriy

AU - Emge, Thomas J.

AU - Krogh-Jespersen, Karsten

AU - Goldman, Alan S

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N2 - A pincer-ligated iridium complex, (PCP)Ir (PCP = κ3-C 6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp3)-O bonds of methyl esters (CH3-O2CR′), methyl tosylate (CH 3-OTs), and certain electron-poor methyl aryl ethers (CH 3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H) [κ2-CH2OC(O)Me] which then affords (PCP-CH 2)Ir(H)(κ2-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ2-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

AB - A pincer-ligated iridium complex, (PCP)Ir (PCP = κ3-C 6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp3)-O bonds of methyl esters (CH3-O2CR′), methyl tosylate (CH 3-OTs), and certain electron-poor methyl aryl ethers (CH 3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H) [κ2-CH2OC(O)Me] which then affords (PCP-CH 2)Ir(H)(κ2-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ2-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

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