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Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study

Bischof, Steven M. and Ess, Daniel H. and Meier, Steven K. and Oxgaard, Jonas and Nielsen, Robert J. and Bhalla, Gaurav and Goddard, William A., III and Periana, Roy A. (2010) Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study. Organometallics, 29 (4). pp. 742-756. ISSN 0276-7333. http://resolver.caltech.edu/CaltechAUTHORS:20100309-110109851

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Abstract

The mechanism of benzene C−H bond activation by [Ir(μ-acac-O,O,C^3)(acac-O,O)(OAc)]_2 (4) and [Ir(μ-acac-O,O,C^3)(acac-O,O)(TFA)]_2 (5) complexes (acac = acetylacetonato, OAc = acetate, and TFA = trifluoroacetate) was studied experimentally and theoretically. Hydrogen−deuterium (H/D) exchange between benzene and CD_(3)COOD solvent catalyzed by 4 (ΔH^‡ = 28.3 ± 1.1 kcal/mol, ΔS^‡ = 3.9 ± 3.0 cal K^(−1) mol^(−1)) results in a monotonic increase of all benzene isotopologues, suggesting that once benzene coordinates to the iridium center, there are multiple H/D exchange events prior to benzene dissociation. B3LYP density functional theory (DFT) calculations reveal that this benzene isotopologue pattern is due to a rate-determining step that involves acetate ligand dissociation and benzene coordination, which is then followed by heterolytic C−H bond cleavage to generate an iridium-phenyl intermediate. A synthesized iridium-phenyl intermediate was also shown to be competent for H/D exchange, giving similar rates to the proposed catalytic systems. This mechanism nicely explains why hydroarylation between benzene and alkenes is suppressed in the presence of acetic acid when catalyzed by [Ir(μ-acac-O,O,C^3)(acac-O,O)(acac-C^3)]_2 (3) (Matsumoto et al. J. Am. Chem. Soc. 2000, 122, 7414). Benzene H/D exchange in CF_(3)COOD solvent catalyzed by 5 (ΔH^‡ = 15.3 ± 3.5 kcal/mol, ΔS^‡ = −30.0 ± 5.1 cal K^(−1) mol^(−1)) results in significantly elevated H/D exchange rates and the formation of only a single benzene isotopologue, (C_(6)H_(5)D). DFT calculations show that this is due to a change in the rate-determining step. Now equilibrium between coordinated and uncoordinated benzene precedes a single rate-determining heterolytic C−H bond cleavage step.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1021/om900036jDOIArticle
http://pubs.acs.org/doi/abs/10.1021/om900036jPublisherArticle
ORCID:
AuthorORCID
Nielsen, Robert J.0000-0002-7962-0186
Goddard, William A., III0000-0003-0097-5716
Periana, Roy A.0000-0001-7838-257X
Additional Information:© 2010 American Chemical Society. Received January 15, 2009. Publication Date (Web): January 26, 2010. We gratefully acknowledge financial support of this research by the Chevron Corporation and The Scripps Research Institute. We thank Yimin Chen for preliminary investigations on anion inhibition studies. The authors also thank Dr. Claas H. Hövelmann and Dr. Brian G. Hashiguchi for helpful discussions.
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Funding AgencyGrant Number
Chevron CorporationUNSPECIFIED
Scripps Research InstituteUNSPECIFIED
Record Number:CaltechAUTHORS:20100309-110109851
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20100309-110109851
Official Citation:Benzene C−H Bond Activation in Carboxylic Acids Catalyzed by O-Donor Iridium(III) Complexes: An Experimental and Density Functional Study Steven M. Bischof, Daniel H. Ess, Steven K. Meier, Jonas Oxgaard, Robert J. Nielsen, Gaurav Bhalla, William A. Goddard III, Roy A. Periana Organometallics 2010 29 (4), 742-756
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17704
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:09 Mar 2010 19:46
Last Modified:22 Sep 2017 05:11

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