- CO2 activation with bulky neutral and cationic phenoxyalanes
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The sterically crowded aluminum diphenolate (2,6-Mes2C 6H3O)2AlEt (2; Mes =2,4,6-Me3C 6H2-) was converted into the ionic species [(2,6-Mes 2C6H3O)2Al]+[CHB 11Cl11]- (6) by ethide abstraction with the silylium salt [Et3Si][CHB11Cl11] or by a combination of β-hydride abstraction and concomitant ethylene elimination with the trityl salt [Ph3C][CHB11Cl11]. Compound 6 consists of solvent-separated ions, and the cation features very short Al···C contacts involving the flanking mesityl groups, leading to an overall distorted-tetrahedral coordination geometry around the aluminum center. Analogous reactions with the diphenolate (2,6-tBu 2-4-MeC6H2O)2AlEt (1) led to tert-butyl transfer to the benzene solvent to afford tert-butylbenzene as the main product. A 1:1 mixture of the triphenolate (2,6-Ph2C 6H3O)3Al and tri-tert-butylphosphine forms a frustrated Lewis pair, which reacts with CO2 at room temperature to give the compound (2,6-Ph2C6H3O) 3AlOC(O)Pt-Bu3 (8). The high Lewis acidity of 6 catalyzes the scrambling of the subsituents of Et3SiH at room temperature to give Et4Si, Et2SiH2, and EtSiH3 and also the reduction of CO2 to d5-toluene (C 6D5CH3) and CH4 at 82 C in d 6-benzene solution.
- Wehmschulte, Rudolf J.,Saleh, Mahmoud,Powell, Douglas R.
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- An alternative route to electrophilic substitution. 2. Aromatic alkylation in the ion neutral complexes formed upon addition of gaseous arenium ions to olefins
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The joint application of mass spectrometric and radiolytic techniques has allowed demonstration of an alternative route to electrophilic aromatic substitution operative in the gas phase, where the Wheland intermediate is formed within the ion-neutral complex (INC) formed upon addition of an arenium ion to an olefin. Experiments involving several representative pairs of arenium ions XC6H6+ (X = H, CH3, CF3) and olefins (C3H6, iC4H8, cC5H8) have provided conclusive evidence for the operation of the above reaction sequence and hence for the occurrence of intracomplex alkylation. The peculiar mechanistic features of the reaction fit a model that identifies the relative basicity of the arene and of the olefin associated in any given INC as the key kinetic factor. The model accounts for the seemingly paradoxical observation that the alkylated products from less activated substrates are formed at relatively higher rates and for the occurrence of consecutive alkylation steps, yielding polyalkylated products of the less activated substrates. The relevance of the work to the theory of the aromatic substitution as a new entry into the reaction manifold of Friedel-Crafts alkylation and to gas-phase ion chemistry, as an irrefutable demonstration of the kinetic role of INCs is briefly discussed.
- Aschi, Massimiliano,Attinà, Marina,Cacace, Fulvio
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- Heterolytic Oxidative Addition of sp2and sp3C-H Bonds by Metal-Ligand Cooperation with an Electron-Deficient Cyclopentadienone Iridium Complex
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Oxidative addition reactions of C-H bonds that generate metal-carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium(I) complex 1 designed for oxidative C-H bond additions. The complex cleaves the various sp2 and sp3 C-H bonds including those in hexane and methane as inferred from their H/D exchange reactions. The hydroxycyclopentadienyl(nitromethyl)iridium(III) complex 2 was formed when the complex was treated with nitromethane, which highlights this elementary metal-ligand cooperative C-H bond oxidative addition reaction. Mechanistic investigations suggested the C-H bond cleavage is mediated by polar functional groups in substrates or another iridium complex. We found that ligands that are more electron-deficient lead to more favorable reactions, in sharp contrast to classical metal-centered oxidative additions. This trend is in good agreement with the proposed mechanism, in which C-H bond cleavage is accompanied by two-electron transfer from the metal center to the cyclopentadienone ligand. The complex was further applied to catalytic transfer-dehydrogenation of tetrahydrofuran (THF).
- Higashi, Takuya,Kusumoto, Shuhei,Nozaki, Kyoko
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supporting information
p. 12999 - 13004
(2021/08/16)
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- Catalytic Reduction of Carbon Dioxide Using Cationic Organoaluminum and -Gallium Compounds
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Ethide abstraction from Et3M (M = Al and Ga), (2,6-Ph2C6H3)AlEt2, 1, and (2,6-Dipp2C6H3)GaEt2, 2 (Dipp = 2,6-iPr2C6H3), usi
- Saleh, Mahmoud,Powell, Douglas R.,Wehmschulte, Rudolf J.
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p. 4810 - 4815
(2018/02/07)
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- Activation of Chlorinated Methanes at the Surface of Nanoscopic Lewis Acidic Aluminum Fluorides
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We report on the activation of chlorinated methanes by the heterogeneous catalysts aluminum chlorofluoride (ACF) and high-surface aluminum fluoride (HS-AlF3) under moderate conditions. For comparison, chlorinated toluenes and 1,2-dichloroethane
- Siwek, Agnieszka K.,Ahrens, Mike,Feist, Michael,Braun, Thomas,Kemnitz, Erhard
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p. 839 - 845
(2017/03/13)
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- Catalytic hydrodefluorination of fluoromethanes at room temperature by silylium-ion-like surface species
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'Al'l about F: Aluminum chlorofluoride (ACF) catalyzes the hydrodefluorination, as well as Friedel-Crafts reactions of fluorinated methanes in the presence of Et3SiH. A surface-bound silylium-ion-like species is considered to be a crucial intermediate in achieving the C-F bond cleavage. Copyright
- Ahrens, Mike,Scholz, Gudrun,Braun, Thomas,Kemnitz, Erhard
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supporting information
p. 5328 - 5332
(2013/06/27)
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- 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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- Deoxygenative reduction of carbon dioxide to methane, toluene, and diphenylmethane with [Et2Al]+ as catalyst
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The strong Lewis acid [Et2Al]+ catalyzes the reduction of carbon dioxide with hydrosilanes under mild conditions to methane. In benzene solution, the side products toluene and diphenylmethane are also obtained through Lewis acid catalyzed benzene alkylation by reaction intermediates. Copyright
- Khandelwal, Manish,Wehmschulte, Rudolf J.
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supporting information; experimental part
p. 7323 - 7326
(2012/09/08)
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- Room Temperature Activation of Aromatic C-H Bonds by Non-Classical Ruthenium Hydride Complexes Containing Carbene Ligands
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Non-classical ruthenium hydride complexes are promising lead structures for the C-H bond activation and functionalization of aromatic compounds. In the present paper, the preparation and crystallographic characterisation of the first organo-metallic complexes bearing dihydrogen ligands and N-heterocyclic carbene ligands in the same coordination sphere are described. The mixed phosphine/ carbene complex [(IMes)Ru(H)2(H2) 2(PCy3)] (IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2- ylidene; 3a) shows a unique reactivity pattern in the inter- and intramolecular activation of C-H bonds. In particular, complex 3a effects a rapid and remarkably selective intermolecular activation of sp2 C-H bonds in simple aromatic compounds at room temperature.
- Giunta, Daniela,H?lscher, Markus,Lehmann, Christian W.,Mynott, Richard,Wirtz, Cornelia,Leitner, Walter
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p. 1139 - 1145
(2007/10/03)
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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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- Structural Study and Reactivity of Carbanions in Solution: Phenyl- and 3-Pyridylacetonitriles
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From the IR and (13)C NMR spectra of Li- and K-associated anionic species 1A,M formed phenylacetonitrile in THF, it appears that monomeric tight ion pairs and THF-solvated aggregates are in equilibrium at 0.25 M concentration; the 0.025 M THF solution for
- Croisat, Denis,Seyden-Penne, Jacqueline,Strzalko, Tekla,Wartski, Lya,Corset, Jacques,Froment, Francoise
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p. 6435 - 6447
(2007/10/02)
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- Isotopic selectivity in the one-electron-promoted cleavage of ring-deuterated naphthylmethyl phenyl ethers and naphthyl benzyl ethers
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(1-Naphthyl)methyl phenyl ether (1) and 1-naphthyl benzyl ether (2) have been allowed to compete against isotopically modified 1 or 2 in reactions with fluoranthene radical anion, F?-, and biphenyl radical anion, B?-. These reactions involve electron transfer followed by CH2-O bond cleavage. Discrimination is observed in favor of 1 when it competes with naphthalene-ring-deuterated 1 (C10D7CH2OC6H5) in reaction with F?-. Discrimination is not observed when the naphthalene ring of 2 is modified. Neither naphthalene-ring-deuterated 1 nor 2 showed isotopic selectivity in reaction with B?-. Small but experimentally significant discriminations are detected for the case of 2 with modified benzyl groups (C6D5CH2 and C6D5CD2) reacting with F?-. The results are interpreted as indicating a transition state for cleavage of 1?- in which the extra electron is substantially located in the π* molecular orbital of the naphthalene ring. Cleavage of 2?- is better viewed as involving a σ*-like transition state.
- Guthrie, Robert D.,Shi, Buchang
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p. 3136 - 3139
(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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