A room temperature direct metal insertion into a nonstrained carbon-carbon bond in solution. C-C vs C-H bond activation

Boris Rybtchinski, Arkadi Vigalok, Yehoshoa Ben-David, David Milstein

Research output: Contribution to journalArticle

156 Citations (Scopus)

Abstract

The diphosphine 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethylbenzene (1a) upon reacting with the rhodium and iridium olefin complexes M2(olefin)4Cl2 (M = Rh, Ir) undergoes rapid, selective metal insertion into the strong unstrained aryl-methyl bond under very mild conditions (room temperature), yielding CIM(CH3)[C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (4a), Ir (7a)). The carbon-carbon bond activation is competitive with a parallel C-H activation process, which results in formation of complexes CIMH(L)[CH2C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (3a), Ir (6a); L = cyclooctene in the case of 6a and is absent in 3a). Complexes 3a and 6a undergo facile C-H reductive elimination (at room temperature (3a) or upon moderate heating (6a)), followed by C-C oxidative addition, resulting in clean formation of 4a and 7a, respectively. The C-C bond activation products are stable under the reaction conditions, demonstrating that this process is the thermo dynamically favorable one. X-ray single-crystal analysis of 4a demonstrates that the rhodium atom is located in the center of a square pyramid, with the methyl group occupying the position trans to the vacant coordination site. Direct kinetic comparison of the C-C and C-H activation processes shows that-in contrast to theoretical calculations-metal insertion into the carbon-carbon bond in this system is not only thermodynamically but also kinetically preferred over the competing insertion into the carbon-hydrogen bond. When the ligand 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethyl-5-methoxybenze ne (1b), bearing the strong electron-donating methoxy group in the position trans to the Ar-CH3 bond to be cleaved, was used instead of 1a, no effect on the reaction rate or on the ratio between the C-H and C-C activation products was observed. Our observations indicate that the C-C oxidative addition proceeds via a three-centered mechanism involving a nonpolar transition state, similar to the one proposed for C-H activation of hydrocarbons. A η2-arene complex is not involved in the C-C activation process.

Original languageEnglish
Pages (from-to)12406-12415
Number of pages10
JournalJournal of the American Chemical Society
Volume118
Issue number49
DOIs
Publication statusPublished - 1996

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Carbon
Metals
Chemical activation
Temperature
Rhodium
Alkenes
Olefins
Iridium
Bearings (structural)
Hydrocarbons
Heating
Hydrogen
X-Rays
Electrons
Ligands
Reaction rates
Hydrogen bonds
Single crystals
X rays
Atoms

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

A room temperature direct metal insertion into a nonstrained carbon-carbon bond in solution. C-C vs C-H bond activation. / Rybtchinski, Boris; Vigalok, Arkadi; Ben-David, Yehoshoa; Milstein, David.

In: Journal of the American Chemical Society, Vol. 118, No. 49, 1996, p. 12406-12415.

Research output: Contribution to journalArticle

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abstract = "The diphosphine 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethylbenzene (1a) upon reacting with the rhodium and iridium olefin complexes M2(olefin)4Cl2 (M = Rh, Ir) undergoes rapid, selective metal insertion into the strong unstrained aryl-methyl bond under very mild conditions (room temperature), yielding CIM(CH3)[C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (4a), Ir (7a)). The carbon-carbon bond activation is competitive with a parallel C-H activation process, which results in formation of complexes CIMH(L)[CH2C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (3a), Ir (6a); L = cyclooctene in the case of 6a and is absent in 3a). Complexes 3a and 6a undergo facile C-H reductive elimination (at room temperature (3a) or upon moderate heating (6a)), followed by C-C oxidative addition, resulting in clean formation of 4a and 7a, respectively. The C-C bond activation products are stable under the reaction conditions, demonstrating that this process is the thermo dynamically favorable one. X-ray single-crystal analysis of 4a demonstrates that the rhodium atom is located in the center of a square pyramid, with the methyl group occupying the position trans to the vacant coordination site. Direct kinetic comparison of the C-C and C-H activation processes shows that-in contrast to theoretical calculations-metal insertion into the carbon-carbon bond in this system is not only thermodynamically but also kinetically preferred over the competing insertion into the carbon-hydrogen bond. When the ligand 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethyl-5-methoxybenze ne (1b), bearing the strong electron-donating methoxy group in the position trans to the Ar-CH3 bond to be cleaved, was used instead of 1a, no effect on the reaction rate or on the ratio between the C-H and C-C activation products was observed. Our observations indicate that the C-C oxidative addition proceeds via a three-centered mechanism involving a nonpolar transition state, similar to the one proposed for C-H activation of hydrocarbons. A η2-arene complex is not involved in the C-C activation process.",
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T1 - A room temperature direct metal insertion into a nonstrained carbon-carbon bond in solution. C-C vs C-H bond activation

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AU - Milstein, David

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N2 - The diphosphine 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethylbenzene (1a) upon reacting with the rhodium and iridium olefin complexes M2(olefin)4Cl2 (M = Rh, Ir) undergoes rapid, selective metal insertion into the strong unstrained aryl-methyl bond under very mild conditions (room temperature), yielding CIM(CH3)[C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (4a), Ir (7a)). The carbon-carbon bond activation is competitive with a parallel C-H activation process, which results in formation of complexes CIMH(L)[CH2C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (3a), Ir (6a); L = cyclooctene in the case of 6a and is absent in 3a). Complexes 3a and 6a undergo facile C-H reductive elimination (at room temperature (3a) or upon moderate heating (6a)), followed by C-C oxidative addition, resulting in clean formation of 4a and 7a, respectively. The C-C bond activation products are stable under the reaction conditions, demonstrating that this process is the thermo dynamically favorable one. X-ray single-crystal analysis of 4a demonstrates that the rhodium atom is located in the center of a square pyramid, with the methyl group occupying the position trans to the vacant coordination site. Direct kinetic comparison of the C-C and C-H activation processes shows that-in contrast to theoretical calculations-metal insertion into the carbon-carbon bond in this system is not only thermodynamically but also kinetically preferred over the competing insertion into the carbon-hydrogen bond. When the ligand 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethyl-5-methoxybenze ne (1b), bearing the strong electron-donating methoxy group in the position trans to the Ar-CH3 bond to be cleaved, was used instead of 1a, no effect on the reaction rate or on the ratio between the C-H and C-C activation products was observed. Our observations indicate that the C-C oxidative addition proceeds via a three-centered mechanism involving a nonpolar transition state, similar to the one proposed for C-H activation of hydrocarbons. A η2-arene complex is not involved in the C-C activation process.

AB - The diphosphine 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethylbenzene (1a) upon reacting with the rhodium and iridium olefin complexes M2(olefin)4Cl2 (M = Rh, Ir) undergoes rapid, selective metal insertion into the strong unstrained aryl-methyl bond under very mild conditions (room temperature), yielding CIM(CH3)[C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (4a), Ir (7a)). The carbon-carbon bond activation is competitive with a parallel C-H activation process, which results in formation of complexes CIMH(L)[CH2C6H(CH3)2(CH2P(t-Bu)2)2] (M = Rh (3a), Ir (6a); L = cyclooctene in the case of 6a and is absent in 3a). Complexes 3a and 6a undergo facile C-H reductive elimination (at room temperature (3a) or upon moderate heating (6a)), followed by C-C oxidative addition, resulting in clean formation of 4a and 7a, respectively. The C-C bond activation products are stable under the reaction conditions, demonstrating that this process is the thermo dynamically favorable one. X-ray single-crystal analysis of 4a demonstrates that the rhodium atom is located in the center of a square pyramid, with the methyl group occupying the position trans to the vacant coordination site. Direct kinetic comparison of the C-C and C-H activation processes shows that-in contrast to theoretical calculations-metal insertion into the carbon-carbon bond in this system is not only thermodynamically but also kinetically preferred over the competing insertion into the carbon-hydrogen bond. When the ligand 1,3-bis[(di-tert-butylphosphino)methyl]-2,4,6-trimethyl-5-methoxybenze ne (1b), bearing the strong electron-donating methoxy group in the position trans to the Ar-CH3 bond to be cleaved, was used instead of 1a, no effect on the reaction rate or on the ratio between the C-H and C-C activation products was observed. Our observations indicate that the C-C oxidative addition proceeds via a three-centered mechanism involving a nonpolar transition state, similar to the one proposed for C-H activation of hydrocarbons. A η2-arene complex is not involved in the C-C activation process.

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