Reactivity of the latent 12-electron fragment [Rh(PiBu3) 2]+with aryl bromides

Aryl-br and phosphine ligand C-H activation

Nell S. Townsend, Adrian B. Chaplin, M Abu Naser, Amber L. Thompson, Nicholas H. Rees, Stuart A. Macgregor, Andrew S. Weller

Research output: Contribution to journalArticle

Abstract

Oxidative addition of aryl bromides to 12-electron [Rh(PiBu 3)2]-[BArF4] (ArF = 3,5-(CF3)2C6H3) forms a variety of products. With p-tolyl bromides, RhIII dimeric complexes result [Rh(PiBu3)2(o/p-MeC6H4)(µ-Br)] 2-[BArF4]2. Similarly, reaction with p-ClC6H4Br gives [Rh(PiBu3) 2(p-ClC6H4)(µ-Br)]2[BAr F4]2. In contrast, the use of o-BrC 6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh(PiBu 2-(CH2CHCH3CH2)}(PiBu 3)(µ-Br)]2-[BArF4]2. Trapping experiments with ortho-biomo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate RhIII complex that then undergoes C-H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rn(PiBu3)2(C6H4OMe)Br]-[BA F4] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H 4SMe)-Br][BArF4]. The anisole-derived complex proceeds to give [Rh-{PiBu2(CH2CHCH3CH 2)}(PiBu3)(µ-Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4OMe)Br] [BArF4] and its onward reactivity to give the products of C-H activation and aryl elimination suggest that it is implicated on the pathway of a s-bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C-H bond cleavage through phosphine-assisted deprotonation of a non-agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C-H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid-state by X-ray crystallography. © 2010 Wiley-VCH. Verlag GmbH & Co. KGaA, Weinheim.

Original languageEnglish
Pages (from-to)8376-8389
Number of pages14
JournalChemistry - A European Journal
Volume16
Issue number28
DOIs
Publication statusPublished - 26 Jul 2010

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phosphine
Bromides
Chemical activation
Ligands
Electrons
Deprotonation
Protonation
X ray crystallography
Toluene
Discrete Fourier transforms
Metals
Nuclear magnetic resonance

Keywords

  • Agostic interactions
  • C-H activation
  • Density functional calculations
  • Transition metals
  • X-ray diffraction

Cite this

Townsend, Nell S. ; Chaplin, Adrian B. ; Abu Naser, M ; Thompson, Amber L. ; Rees, Nicholas H. ; Macgregor, Stuart A. ; Weller, Andrew S. / Reactivity of the latent 12-electron fragment [Rh(PiBu3) 2]+with aryl bromides : Aryl-br and phosphine ligand C-H activation. In: Chemistry - A European Journal. 2010 ; Vol. 16, No. 28. pp. 8376-8389.
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abstract = "Oxidative addition of aryl bromides to 12-electron [Rh(PiBu 3)2]-[BArF4] (ArF = 3,5-(CF3)2C6H3) forms a variety of products. With p-tolyl bromides, RhIII dimeric complexes result [Rh(PiBu3)2(o/p-MeC6H4)(µ-Br)] 2-[BArF4]2. Similarly, reaction with p-ClC6H4Br gives [Rh(PiBu3) 2(p-ClC6H4)(µ-Br)]2[BAr F4]2. In contrast, the use of o-BrC 6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh(PiBu 2-(CH2CHCH3CH2)}(PiBu 3)(µ-Br)]2-[BArF4]2. Trapping experiments with ortho-biomo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate RhIII complex that then undergoes C-H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rn(PiBu3)2(C6H4OMe)Br]-[BA F4] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H 4SMe)-Br][BArF4]. The anisole-derived complex proceeds to give [Rh-{PiBu2(CH2CHCH3CH 2)}(PiBu3)(µ-Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4OMe)Br] [BArF4] and its onward reactivity to give the products of C-H activation and aryl elimination suggest that it is implicated on the pathway of a s-bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C-H bond cleavage through phosphine-assisted deprotonation of a non-agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C-H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid-state by X-ray crystallography. {\circledC} 2010 Wiley-VCH. Verlag GmbH & Co. KGaA, Weinheim.",
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Reactivity of the latent 12-electron fragment [Rh(PiBu3) 2]+with aryl bromides : Aryl-br and phosphine ligand C-H activation. / Townsend, Nell S.; Chaplin, Adrian B.; Abu Naser, M; Thompson, Amber L.; Rees, Nicholas H.; Macgregor, Stuart A.; Weller, Andrew S.

In: Chemistry - A European Journal, Vol. 16, No. 28, 26.07.2010, p. 8376-8389.

Research output: Contribution to journalArticle

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T1 - Reactivity of the latent 12-electron fragment [Rh(PiBu3) 2]+with aryl bromides

T2 - Aryl-br and phosphine ligand C-H activation

AU - Townsend, Nell S.

AU - Chaplin, Adrian B.

AU - Abu Naser, M

AU - Thompson, Amber L.

AU - Rees, Nicholas H.

AU - Macgregor, Stuart A.

AU - Weller, Andrew S.

PY - 2010/7/26

Y1 - 2010/7/26

N2 - Oxidative addition of aryl bromides to 12-electron [Rh(PiBu 3)2]-[BArF4] (ArF = 3,5-(CF3)2C6H3) forms a variety of products. With p-tolyl bromides, RhIII dimeric complexes result [Rh(PiBu3)2(o/p-MeC6H4)(µ-Br)] 2-[BArF4]2. Similarly, reaction with p-ClC6H4Br gives [Rh(PiBu3) 2(p-ClC6H4)(µ-Br)]2[BAr F4]2. In contrast, the use of o-BrC 6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh(PiBu 2-(CH2CHCH3CH2)}(PiBu 3)(µ-Br)]2-[BArF4]2. Trapping experiments with ortho-biomo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate RhIII complex that then undergoes C-H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rn(PiBu3)2(C6H4OMe)Br]-[BA F4] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H 4SMe)-Br][BArF4]. The anisole-derived complex proceeds to give [Rh-{PiBu2(CH2CHCH3CH 2)}(PiBu3)(µ-Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4OMe)Br] [BArF4] and its onward reactivity to give the products of C-H activation and aryl elimination suggest that it is implicated on the pathway of a s-bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C-H bond cleavage through phosphine-assisted deprotonation of a non-agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C-H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid-state by X-ray crystallography. © 2010 Wiley-VCH. Verlag GmbH & Co. KGaA, Weinheim.

AB - Oxidative addition of aryl bromides to 12-electron [Rh(PiBu 3)2]-[BArF4] (ArF = 3,5-(CF3)2C6H3) forms a variety of products. With p-tolyl bromides, RhIII dimeric complexes result [Rh(PiBu3)2(o/p-MeC6H4)(µ-Br)] 2-[BArF4]2. Similarly, reaction with p-ClC6H4Br gives [Rh(PiBu3) 2(p-ClC6H4)(µ-Br)]2[BAr F4]2. In contrast, the use of o-BrC 6H4Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh(PiBu 2-(CH2CHCH3CH2)}(PiBu 3)(µ-Br)]2-[BArF4]2. Trapping experiments with ortho-biomo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate RhIII complex that then undergoes C-H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rn(PiBu3)2(C6H4OMe)Br]-[BA F4] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu3)2(C6H 4SMe)-Br][BArF4]. The anisole-derived complex proceeds to give [Rh-{PiBu2(CH2CHCH3CH 2)}(PiBu3)(µ-Br)]2[BArF4]2, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu3)2(C6H4OMe)Br] [BArF4] and its onward reactivity to give the products of C-H activation and aryl elimination suggest that it is implicated on the pathway of a s-bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C-H bond cleavage through phosphine-assisted deprotonation of a non-agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C-H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid-state by X-ray crystallography. © 2010 Wiley-VCH. Verlag GmbH & Co. KGaA, Weinheim.

KW - Agostic interactions

KW - C-H activation

KW - Density functional calculations

KW - Transition metals

KW - X-ray diffraction

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