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

doi:10.1002/chem.201000554

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

School of Chemistry

Research output: Contribution to journal › Article › peer-review

16 Citations (Scopus)

Abstract

Oxidative addition of aryl bromides to 12-electron [Rh(PiBu ₃)₂]-[BAr^F₄] (Ar^F = 3,5-(CF₃)₂C₆H₃) forms a variety of products. With p-tolyl bromides, Rh^III dimeric complexes result [Rh(PiBu₃)₂(o/p-MeC₆H₄)(μ-Br)] ₂-[BAr^F₄]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-[BAr^F₄]₂. Trapping experiments with ortho-biomo anisole or ortho-bromo thioanisole indicate that a possible intermediate for this process is a low-coordinate Rh^III 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][BAr^F₄]. The anisole-derived complex proceeds to give [Rh-{PiBu₂(CH₂CHCH₃CH ₂)}(PiBu₃)(μ-Br)]₂[BAr^F ₄]₂, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu₃)₂(C₆H₄OMe)Br] [BAr^F₄] 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 σ-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.

Original language	English
Pages (from-to)	8376-8389
Number of pages	14
Journal	Chemistry - A European Journal
Volume	16
Issue number	28
DOIs	https://doi.org/10.1002/chem.201000554
Publication status	Published - 26 Jul 2010

Keywords

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

Access to Document

10.1002/chem.201000554

Cite this

@article{6fca1aa5c29b4c0abfbee715ecae059b,

title = "Reactivity of the latent 12-electron fragment [Rh(PiBu3) 2]+with aryl bromides: Aryl-br and phosphine ligand C-H activation",

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[BArF 4]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 σ-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.",

keywords = "Agostic interactions, C-H activation, Density functional calculations, Transition metals, X-ray diffraction",

author = "Townsend, {Nell S.} and Chaplin, {Adrian B.} and Naser, {M. Abu} and Thompson, {Amber L.} and Rees, {Nicholas H.} and Macgregor, {Stuart A.} and Weller, {Andrew S.}",

year = "2010",

month = jul,

day = "26",

doi = "10.1002/chem.201000554",

language = "English",

volume = "16",

pages = "8376--8389",

journal = "Chemistry - A European Journal",

issn = "0947-6539",

publisher = "John Wiley & Sons, Ltd",

number = "28",

}

TY - JOUR

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 - Naser, M. Abu

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[BArF 4]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 σ-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.

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[BArF 4]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 σ-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.

KW - Agostic interactions

KW - C-H activation

KW - Density functional calculations

KW - Transition metals

KW - X-ray diffraction

UR - http://www.scopus.com/inward/record.url?scp=77954846478&partnerID=8YFLogxK

U2 - 10.1002/chem.201000554

DO - 10.1002/chem.201000554

M3 - Article

AN - SCOPUS:77954846478

SN - 0947-6539

VL - 16

SP - 8376

EP - 8389

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

IS - 28

ER -

Reactivity of the latent 12-electron fragment [Rh(PiBu₃) ₂]⁺with aryl bromides: Aryl-br and phosphine ligand C-H activation

Abstract

Keywords

Access to Document

Other files and links

Fingerprint

Cite this