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C-H bond activation by cationic iridium (III) NHC complexes: A combined experimental and computational study

Citation

Meredith, JM and Robinson, R and Goldberg, KI and Kiminsky, W and Heinekey, DM, C-H bond activation by cationic iridium (III) NHC complexes: A combined experimental and computational study, Organometallics, 31, (5) pp. 1879-1887. ISSN 0276-7333 (2012) [Refereed Article]

Copyright Statement

Copyright 2012 American Chemical Society

DOI: doi:10.1021/om2012166

Abstract

The cationic complexes [Cp*Ir(NHC)Me(solv)]+[MeB- (C6F5)3]− were prepared and studied as models for methane oxyfunctionalization catalysts (Cp* = 5-C5Me5; NHC = 1,3,4,5-tetramethylimidazol- 2-ylidene (MeIMe, 3a), 1,3-dimethylimidazol-2-ylidene (IMe, 3b), 1,3-dimethylbenzimidazol-2-ylidene (BIMe, 3c); solv = solvent or open site). These complexes were targeted on the basis of the C−H bond activation reactions of the previously reported complexes [Cp*Ir(PMe3)R]+ (R = Me, H) and the general robustness of Ir−NHC complexes under oxidizing conditions. The syntheses of the new iridium(III)complexes Cp*Ir(NHC)Me2 are described (NHC = MeIMe (4a), IMe (4b), BIMe (4c)). When 4a−c were allowed to react with B(C6F5)3 in CH2Cl2, the methyl abstraction products [Cp*Ir(NHC)Me(solv)]+[MeB(C6F5)3]Y (3a−c) were produced. Complexes 3a−c reacted with arenes to form the aryl complexes [Cp*Ir(NHC)Ar(solv)]+[MeB(C6F5)3]Y and methane (Ar = C6H5 (7), C6H4F (8)). Complexes 3a−c reacted very slowly with alkanes; the slow reaction rate is attributed to steric congestion due to the NHC ligand. DFT calculations support this hypothesis: the barriers to C−H activation are in qualitative agreement with the empirical reaction rates, and the C−H activation transition state structures show significant steric crowding. Several of these complexes have been analyzed by X-ray diffraction.

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Inorganic Chemistry
Research Field:Transition Metal Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Robinson, R (Dr Robert Robinson)
ID Code:81047
Year Published:2012
Web of Science® Times Cited:13
Deposited By:Chemistry
Deposited On:2012-11-21
Last Modified:2015-02-08
Downloads:0

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