- Catalytic arene H/D exchange with novel rhodium and iridium complexes
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Three novel pendant acetate complexes, [Rh(bdmpza)Cl3] -M+, [Rh(bdmpza)Cl2(py)], and [Ir(bdmpza)Cl3]-M+ (bdmpza = bis(3,5-dimethylpyrazol-1-yl) acetate, M+ = Li+, Na +), were synthesized. Abstraction of halide from these complexes with silver salts yielded species capable of C-H activation of arenes. The catalytic H/D exchange reaction between benzene and trifluoroacetic acid-d was optimized, and these conditions were used to evaluate H/D exchange in other arenes. Branched alkyl substituents in alkyl aromatics showed an affinity toward deuterium exchange in the β-alkyl position only. DFT calculations were performed to determine the mechanism of H/D exchange.
- Rhinehart, Jennifer L.,Manbeck, Kimberly A.,Buzak, Sara K.,Lippa, Geoffrey M.,Brennessel, William W.,Goldberg, Karen I.,Jones, William D.
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experimental part
p. 1943 - 1952
(2012/04/23)
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- Arene Activation with Mercury(II) and Thallium(III) Electrophiles. Mechanistic Relevance of Charge-Transfer Transitions in ?-Complexes as Intermediates
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The activation of various aromatic hydrocarbons by mercuration and thallation proceeds via ?-complexes, as observed by the transient charge-transfer (CT) absorption spectra.Quantitative spectrophotometric analysis of (a) the association constants K and (b) the second-order rate constants k2 establishes the reactive forms of the electrophiles to be Hg(O2CCF3)2 and Tl(O2CCF3)2(1+), both in ?-complex formation as well as in aromatic metalation.The direct participation by these isoelectronic and isostructural species presents a unique opportunity to examine arene activation with electrophiles which primarily differ only in the charge they bear.A detailed comparison of the CT excitation energies and the reactivities of various arenes relative to steric, kinetic isotope, and solvent effects in mercuration and thallation reveals unusual similarities.At the same time the observation of arene cations as key intermediates in thallation, but not in mercuration, leads to puzzling incongruities.The paradox is analyzed in the context of merging stepwise (electron-transfer) and concerted (electrophilic) mechanisms.
- Lau, W.,Kochi, J. K.
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p. 6720 - 6732
(2007/10/02)
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- Thermoneutral Isotope Exchange Reactions of Cations in the Gas Phase
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Rate constants have been measured for reactions of the type AD2+ + MH --> MD + ADH+, where AD2+ is CD3CND+, CD3CDOD+, (CD3COCD3)D+, or (C2D5)2OD+ and the MH molecules are alcohols, acids, mercaptanes, H2S, AsH3, PH3, or aromatic molecules.Rate constants are also presented for the reactions ArHD+ + D2O --> ArDD+ + HDO, where ArHD+ is a deuteronated aromatic molecule and ArDD+ is the same species with a D atom incorporated on the ring.In all but two cases, the competing deuteron transfer is sufficiently endothermic that it cannot be observed under the conditions of the ICR experiments at 320 - 420 K.The efficiencies of the isotope exchange reactions are interpreted in terms of estimated potential surface cross sections for the reactions AD2+ + MH --> 2+*MH> --> +> --> +*MD> --> ADH+ + MD.When the formation of the +> complex is estimated to be thermoneutral or slightly endothermic, the isotope exchange process is inefficient (probability of a reactive collision 2+*MH> --> +> is exothermic.For most of the systems, trends in reaction efficiency appear to be related to factors such as dipole moments of reactant species (or for aromatic compounds, the electron-donating or -withdrawing properties of ring substituents) which influence the relative orientation of the two reactant species in the complex.
- Ausloos, P.,Lias, S. G.
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p. 3641 - 3647
(2007/10/02)
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