- Catalytic deuteration of C(sp2)-H bonds of substituted (Hetero)arenes in a Pt(II) CNN-pincer complex/2,2,2Trifluoroethanol-d1 system: Effect of substituents on the reaction rate and selectivity
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Thirty four (hetero)arene derivatives have been tested in catalytic H/D exchange reactions involving their C(sp2)- H bonds and 2,2,2-trifluoroethanol-d1 (TFE-d1) in the presence of the homogeneous Pt(II) complex 1 supported by a sulfonated CNN-pincer ligand at 80 °C. The 18 substrates, including one pharmaceutical (naproxen), that are stable in the presence of 1 and are active in the H/D exchange reaction have been characterized by their position-specific extent of deuteration and, in a number of cases, the reaction kinetic selectivity. For the most reactive substrates the extent of deuteration approaches the expected statistical distribution of the exchangeable H and D atoms: e.g., 67-69% for phenol after 23 h and 88% for indole β-CH bonds after 45 min. For a few substrates (N,N-dimethylaniline, indole, nitrobenzene) the H/D exchange is highly position selective. No satisfactory correlation was found between the position-specific (meta, para) H/D exchange rate constants for X-monosubstituted benzenes and Hammett σX constants. This observation was proposed to be related to the concerted nature of the CH bond activation, the rate-determining CH bond oxidative addition at a Pt(II) center. A novel scale of Hammett σMX constants was introduced to characterize the reactivity of C(sp2)-H bonds in transition-metal-mediated reactions. The experimentally determined position-specific Gibbs energies of activation of the H/D exchange in substituted benzenes (meta and para positions) as well as in thiophene (α and β positions) were matched satisfactorily using DFT calculations.
- Kramer, Morgan,Watts, David,Vedernikov, Andrei N.
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supporting information
p. 4102 - 4114
(2020/11/30)
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- Arene-mercury complexes stabilized by aluminum and gallium chloride: Catalysts for H/D exchange of aromatic compounds
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Dissolution of Hg(arene)2(MCI4)2 [arene = C6H5Me, C6H5Et, o-C6H4Me2, C6H3-1,2,3-Me3; M = Al, Ga] in C6D6 results in a rapid H/D exchange and the formation of the appropriate dn-arene and C6D5H. H/D exchange is also observed between C6D6 and the liquid clathrate ionic complexes, [Hg(arene)2(MCl4)]-[MCl4], formed by dissolution of HgCl2 and MCl3 in C6H6, m-C6H4Me2, or p-C6H4Me2. The H/D exchange reaction is found to be catalytic with respect to Hg(arene)2(MCl4)2 and independent of the initial arene ligand. Reaction of a 1:1 ratio Of C6H5Me and C6D6 with 6H5Me)2(MCl4)2 results in an equilibrium mixture of all isotopic isomers: C6H5-xDxMe and C6D6-xHx (x = 0-5). DFT calculations on the model system, Hg(C6H6)2(AlCl4)2 and [Hg(C6H6)2(AlCl4)+, show that the charge on the carbon and proton associated with the shortest Hg···C interactions is significantly higher than that on uncomplexed benzene or HgCl2(C6H6)2. The protonation of benzene by either Hg(C6H6)2(AlCl4)2 or [Hg(C6H6)2(AlCl4)]+ was calculated to be thermodynamically favored in comparison to protonation of benzene by HO2CCF3, a known catalyst for arene H/D exchange. Arene exchange and intramolecular hydrogen transfer reactions are also investigated by DFT calculations.
- Borovik, Alexander S.,Barron, Andrew R.
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p. 3743 - 3748
(2007/10/03)
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- Chemical pressure effect by selective deuteration in the molecular-based conductor, 2,5-dimethyl-N,N'-dicyano-p-benzoquinone immine-copper salt, (DMe-DCNQI)2Cu
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The mixed-valence copper salt of DMe-DCNQI91, where DMe-DCNQI=2,5-dimethyl-N,N'-dicyano-p-benzoquinone diimine) is a molecular conductor whose electrical and magnetic properties are quite sensitive to pressure.We have performed selective deuteriation of the molecule 1.By control of the position and number of deuterium atoms, the low-pressure region (ca. 500 bar) in the pressure-temperature phase diagram of (1)2Cu was reproduced at ambient pressure.The equivalency of the deuteriation and pressure effects is explained from steric origins; 'contraction' aroused by the slightly shorter C-D bond (steric isotope effect) and 'constriction' by pressure.
- Aonuma, Shuji,Sawa, Hiroshi,Kato, Reizo
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p. 1541 - 1550
(2007/10/02)
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- Ipso Nitration. Solvolytic Behavior of 1,4-Dimethyl-4-nitrohexadienyl Acetate and 1,4-Dimethyl-4-nitrocyclohexadienol
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The solvolytic rearomatizations of the E and Z isomers of 1,4-dimethyl-4-nitrocyclohexadienyl acetate (1) have been examined in aqueous ethanol and in sulfuric acid solutions.Solvolysis of 1 in aqueous ethanol involves the elimination of nitrous acid and the migration of the acetoxyl group to yield 2,5-dimethylphenyl acetate.The kinetic behavior of this solvolytic reaction parallels that of the secondary adduct 4-nitro-3,4,5-trimethylcyclohexadienyl acetate (2).No kinetic isotope effects were detected when 1,4-dimethyl-4-nitrocyclohexadienyl-2,3,5,6-d4 acetate (1-d4) or 1,4-dimethyl-4-nitrocyclohexadienyl-Me-d6 (1-d6) were used as substrates.The collected data suggest a rate-limiting loss of nitrile ion from 1 followed by migration of the acetoxyl group and proton loss.The behavior of Z and E isomers of 1,4-dimethyl-4-nitrocyclohexadienol (3) in aqueous ethanol differs from that of 1 in several ways.The major product of solvolysis is 2,4-dimethylphenol.The rates of solvolysis of the stereoisomers of 3 do not differ appreciably one from another, and the spectral yield is only 30-40percent of that anticipated.These differences are taken to reflect a rate-limiting migration in the solvolysis of 3 rather than a rate-limiting loss of nitrate ion.Solvolysis of 1 in greater than 77percent sulfuric acid gives 1,4-dimethyl-2-nitrobenzene in quantitative yield.The yield of nitro aromatic falls off smoothly as the acid concentration is lowered toward 50percent.Within the 70-50percent acid range, the yield of side-chain substitution products appears to increase, hold roughly constant, and then decrease.Larger yields of nitro aromatic and smaller yields of side-chain substitution product are found when 1-d6 is used as a reactant.The solvolyses in strong acids are discussed in terms of re-formation of the ipso ion and subsequent partitioning.
- Geppert, J. T.,Johnson, M. W.,Myhre, P. C.,Woods, S. P.
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p. 2057 - 2062
(2007/10/02)
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- The Radical Ions of 4,5,7,8-Tetramethylparacyclophane
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By the use of strong oxidising and reducing agents, 4,5,7,8-tetramethylparacyclophane (II) has been converted to its radical cation (II+.) and to its radical anion (II-.).These radical ions, as well as those generated from the 1
- Bruhin, Juerg,Gerson, Fabian,Ohya-Nishiguchi, Hiroaki
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p. 1045 - 1050
(2007/10/02)
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