Arene C−H Bond Activation and Arene Oxidative Coupling by Cationic Palladium(II) Complexes
Abstract
N,N'-Diaryl-α-diimine-ligated Pd(II) dimethyl complexes (^(tBu)2^(Ar)DAB^(Me))PdMe_2 and {(CF_3)_2^(Ar)DAB^(Me)}PdMe_2 {^(tBu)2^(Ar)DAB^(Me): ArNC═(CH_3)−C(CH_3═NAr, Ar=3,5-di-tert-butylphenyl; (CF_3)_2^(Ar)DAB^(Me):Ar = 3,5-bis(trifluoromethyl)phenyl} undergo protonolysis with HBF_4(aq) in trifluoroethanol (TFE) to form cationic complexes [(α-diimine)Pd(CH_3)(H_2O)][BF_4]. The cations activate benzene C−H bonds at room temperature. Kinetic analyses reveal trends similar to those observed for the analogous platinum complexes: the C−H activation step is rate-determining (KIE = 4.1 ± 0.5) and is inhibited by H_2O. The kinetic data are consistent with a mechanism in which benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway. Following benzene C−H activation under 1 atm O_2, the products of the reaction are biphenyl and a dimeric μ-hydroxide complex, [(α-diimine)Pd(OH)]_2[BF_4]_2. The Pd(0) formed in the reaction is reoxidized by O_2 to the dimeric μ-hydroxide complex after the oxidative C−C bond formation. The regioselectivity of arene coupling was investigated with toluene and α,α,α-trifluorotoluene as substrates.
Additional Information
© 2003 American Chemical Society. Received 5 May 2003. Published online 14 August 2003. Published in print 1 September 2003. This work has been generously supported by BP. L.J.A. thanks the National Science Foundation for a Graduate Research Fellowship. J.P.S. thanks the National Institutes of Health for an NRSA Postdoctoral Fellowship. D.M.K. thanks the Caltech Student-Faculty Programs Office and Thomas and Ruth Hayes for a Summer Undergraduate Research Fellowship (SURF). We thank Dr. Michael W. Day and Lawrence M. Henling for crystallography assistance.Attached Files
Supplemental Material - om0303294_s.pdf
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Additional details
- Eprint ID
- 75014
- Resolver ID
- CaltechAUTHORS:20170310-073002998
- NSF Graduate Research Fellowship
- NIH Postdoctoral Fellowship
- Caltech Student-Faculty Programs Office
- Caltech Summer Undergraduate Research Fellowship (SURF)
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2017-03-10Created from EPrint's datestamp field
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2021-11-15Created from EPrint's last_modified field