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., Naser, M. Abu, Thompson, Amber L., Rees, Nicholas H., Macgregor, Stuart A. and Weller, Andrew S.. (2010) Reactivity of the latent 12-electron fragment [Rh(PiBu3)2]+ with aryl bromides : aryl-Br and phosphine ligand C-H activation. Chemistry: A European Journal, Vol.16 (No.28). pp. 8376-8389. ISSN 0947-6539Full text not available from this repository.
Official URL: http://dx.doi.org/10.1002/chem.201000554
Oxidative addition of aryl bromides to 12-electron [Rh(PiBu(3))(2)]-[BAr(4)(F)] (Ar(F)=3,5-(CF(3))(2)C(6)H(3)) forms a variety of products. With p-tolyl bromides. Rh(III) dimeric complexes result [Rh(PiBu(3))(2)(o/p-MeC(6)H(4))(mu Br)](2)-[BAr(4)(F)](2). Similarly, reaction with p-ClC(6)H(4)Br gives [Rh(PiBu(3))(2)(p-ClC(6)H(4))(mu-Br)](2)[BAr(4)(F)](2). In contrast, the use of o-BrC(6)H(4)Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C-H activation: [Rh(PiBu(2)-(CH(2)CHCH(3)CH(2))](PiBu(3))(mu-Br)](2)- [BAr(4)(F)](2). Trapping experiments with ortho-bromo 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, [Rh(PiBu(3))(2)(C(6)H(4)OMe)Br][BAr(4)(F)] (the solid-state structure of the 5-methyl substituted analogue is reported) and [Rh(PiBu(3))(2)(C(6)H(4)SMe)-Br][BAr(4)(F)]. The anisole-derived complex proceeds to give [Rh-PiBu(2)(CH(2)CHCH(3)CH(2))}(PiBu(3))(mu- Br)](2)[BAr(4)(F)](2), whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu(3))(2)(C(6)H(4)OMe)Br[BAr(4)(F)] 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 o-bond metathesis reaction, a hypothesis strengthened by OFT 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.
|Item Type:||Journal Article|
|Subjects:||Q Science > QD Chemistry|
|Divisions:||Faculty of Science > Chemistry|
|Library of Congress Subject Headings (LCSH):||Activation (Chemistry), Hydrocarbons, Density functionals, Transition metals, X-rays -- Diffraction, Phosphine|
|Journal or Publication Title:||Chemistry: A European Journal|
|Publisher:||Wiley - V C H Verlag GmbH & Co. KGaA|
|Official Date:||26 July 2010|
|Page Range:||pp. 8376-8389|
|Access rights to Published version:||Restricted or Subscription Access|
 M. Portnoy, D. Milstein, Organometallics 1993, 12, 1665 – 1673; J. P.
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