- Calcium-Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores
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Coupled dinuclear copper oxygen cores (Cu2O2) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O2 transport and substrate oxidation in many organisms. μ-1,2-cis peroxido dicoppe
- Ertem, Mehmed Z.,Harland, Jill B.,Lehnert, Nicolai,Musselman, Bradley W.,Robinson, Jerome R.,Vargo, Natasha P.
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- Silicon Tetrakis(trifluoromethanesulfonate): A Simple Neutral Silane Acting as a Soft and Hard Lewis Superacid
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A facile synthesis and isolation of pristine silicon tetrakis(trifluoromethanesulfonate), Si(OTf)4, is reported, acting as the first neutral silicon-based Lewis superacid suitable towards soft and hard Lewis bases. Its OTf groups have a dual function: they are excellent leaving groups and modulate the degree of reactivity towards soft and hard Lewis bases. Exposed to soft Lewis donors, Si(OTf)4 leads to [L2Si(OTf)4] complexes (L=isocyanide, thioether and carbonyl compounds) with retention of all Si?OTf bonds. In contrast, it can cleave C?X bonds (X=F, Cl) of hard organic Lewis bases with a high tendency to form SiX4 (X=F, Cl) after halide/triflate exchange. Most notable, Si(OTf)4 allows a gentle oxydefluorination of mono- and bis(trifluoromethyl)benzenes, resulting in the formation of the corresponding benzoylium species, which are stabilized by the weakly coordinating [Si(OTf)6] dianion.
- Driess, Matthias,Hermannsdorfer, André
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supporting information
p. 13656 - 13660
(2021/05/03)
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- Lewis Acidity Scale of Diaryliodonium Ions toward Oxygen, Nitrogen, and Halogen Lewis Bases
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Equilibrium constants for the associations of 17 diaryliodonium salts Ar2I+X- with 11 different Lewis bases (halide ions, carboxylates, p-nitrophenolate, amines, and tris(p-anisyl)phosphine) have been investigated by titrations followed by photometric or conductometric methods as well as by isothermal titration calorimetry (ITC) in acetonitrile at 20 °C. The resulting set of equilibrium constants KI covers 6 orders of magnitude and can be expressed by the linear free-energy relationship lg KI = sI LAI + LBI, which characterizes iodonium ions by the Lewis acidity parameter LAI, as well as the iodonium-specific affinities of Lewis bases by the Lewis basicity parameter LBI and the susceptibility sI. Least squares minimization with the definition LAI = 0 for Ph2I+ and sI = 1.00 for the benzoate ion provides Lewis acidities LAI for 17 iodonium ions and Lewis basicities LBI and sI for 10 Lewis bases. The lack of a general correlation between the Lewis basicities LBI (with respect to Ar2I+) and LB (with respect to Ar2CH+) indicates that different factors control the thermodynamics of Lewis adduct formation for iodonium ions and carbenium ions. Analysis of temperature-dependent equilibrium measurements as well as ITC experiments reveal a large entropic contribution to the observed Gibbs reaction energies for the Lewis adduct formations from iodonium ions and Lewis bases originating from solvation effects. The kinetics of the benzoate transfer from the bis(4-dimethylamino)-substituted benzhydryl benzoate Ar2CH-OBz to the phenyl(perfluorophenyl)iodonium ion was found to follow a first-order rate law. The first-order rate constant kobs was not affected by the concentration of Ph(C6F5)I+ indicating that the benzoate release from Ar2CH-OBz proceeds via an unassisted SN1-type mechanism followed by interception of the released benzoate ions by Ph(C6F5)I+ ions.
- Legault, Claude Y.,Mayer, Robert J.,Mayr, Herbert,Ofial, Armin R.
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supporting information
(2020/03/13)
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- Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate
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The ionic iridacycle [(2-phenylenepyridine-κN,κC)IrCp?(NCMe)][BArF24] ([2][BArF24]) displays a remarkable capability to catalyze the O-dehydrosilylation of alcohols at room temperature (0.4 × 103 3, 8 × 103 i 5 h-1 for primary alcohols) that is explained by its exothermic reaction with Et3SiH, which affords the new cationic hydrido-Ir(III)-silylium species [3][BArF24]. Isothermal calorimetric titration (ITC) indicates that the reaction of [2][BArF24] with Et3SiH requires 3 equiv of the latter and releases an enthalpy of -46 kcal/mol in chlorobenzene. Density functional theory (DFT) calculations indicate that the thermochemistry of this reaction is largely dominated by the concomitant bis-hydrosilylation of the released MeCN ligand. Attempts to produce [3][BF4] and [3][OTf] salts resulted in the formation of a known neutral hydrido-iridium(III) complex, i.e. 4, and the release of Et3SiF and Et3SiOTf, respectively. In both cases formation of the cationic μ-hydrido-bridged bis-iridacyclic complexes [5][BF4] and [5][OTf], respectively, was observed. The structure of [5][OTf] was established by X-ray diffraction analysis. Conversion of [3][BArF24] into 4 upon reaction with either 4-N,N-dimethylaminopyridine or [nBu4][OTf] indicates that the Ir center holds a +III formal oxidation state and that the Et3Si+ moiety behaves as a Z-type ligand according to Green's formalism. [3][BArF24], which was trapped and structurally characterized and its electronic structure investigated by state-of-the-art DFT methods (DFT-D, EDA, ETS-NOCV, QTAIM, ELF, NCI plots and NBO), displays the features of a cohesive hydridoiridium(III)→silylium donor-acceptor complex. This study suggests that the fate of [3]+ in the O-dehydrosilylation of alcohols is conditioned by the nature of the associated counteranion and by the absence of Lewis base in the medium capable of irreversibly capturing the silylium species.
- Hamdaoui, Mustapha,Ney, Marjolaine,Sarda, Vivien,Karmazin, Lydia,Bailly, Corinne,Sieffert, Nicolas,Dohm, Sebastian,Hansen, Andreas,Grimme, Stefan,Djukic, Jean-Pierre
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p. 2207 - 2223
(2016/07/21)
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- Atom transfer radical addition (ATRA) catalyzed by copper complexes with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) ligand
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Synthesis, characterization, electrochemical studies and ATRA activity of copper complexes with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) ligand in the presence of ascorbic acid as a reducing agent were reported. [CuII(TPEN′)Br][Br] (TPEN′ denotes tetracoordinated ligand) catalyst showed a very low activity in ATRA of CBr4 to 1-octene, methyl methacrylate, methyl acrylate and styrene in methanol, which is a typical solvent used for ATRA reactions employing ascorbic acid. On the contrary, the yields and stereoselectivity towards monoadduct formation were dramatically increased in slightly polar but aprotic acetone. Based on molecular structures of isolated [CuII(TPEN)][BPh4] and [CuII(TPEN′)Br][Br] complexes, as well as UV-Vis and cyclic voltammetry studies, an equilibrium was proposed involving inactive [CuII(TPEN)]2+ and ATRP active [CuII(TPEN′)Br]+ cations The halidophilicity of the bromide-based deactivating complex ([CuII(TPEN′)Br][Br]) decreased approximately 750 times upon changing the solvent from acetone (KBr = 3000 ± 230) to methanol (KBr = 4.1 ± 0.1), explaining poor catalytic activity in methanol. In acetone, [CuII(TPEN′)Br][Br] complex was nearly as active in ATRA reactions employing ascorbic acid as previously reported [CuII(TPMA)Br][Br].
- Kaur, Aman,Gorse, Erin E.,Ribelli, Thomas G.,Jerman, Callista C.,Pintauer, Tomislav
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p. 246 - 252
(2015/03/04)
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- METHOD FOR PREPARATION OF MONONITRATED AROMATIC COMPOUNDS
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The invention discloses a method for preparation of mononitrated aromatic compounds in a liquid-liquid biphasic solvent system with aqueous nitric acid as one phase and ionic liquids (ILs) as the second phase, wherein the nitric acid is continuously exchanged during the reaction, or the water, that is generated during the reaction, is removed by addition of NO2 and an oxidizing agent during the reaction.
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Page/Page column 20
(2012/12/13)
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- Efficient method for varying the anions in quaternary onium halides
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Quaternary onium salts of halides can be efficiently converted into the corresponding quaternary onium salts of various anions [NO3 -, BF4-, PF6-, CF 3SO3-, CH3SO3 -, ClO4-, p-CH3C6H 4SO3-, CF3CO2 -, 2,4-(NO2)2C6H3O -] by treating the onium halide with trimethyl phosphate under neat condition in the presence of an equivalent amount of conjugate acid of the desired anion.
- Jeon, Jong Yeob,Varghese, Jobi Kodiyan,Park, Ji Hae,Lee, Suck-Hyun,Lee, Bun Yeoul
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experimental part
p. 3566 - 3569
(2012/08/14)
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- Interaction between methanol and the Cl-, Br-, I-, NO3-, ClO4-, BF4-, SO3CF3- and PF6- anions studied by FTIR spectroscopy
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The interaction between methanol and the Cl-, Br-, I-, NO3-, ClO4-, BF4-, SO3CF3- and PF6- anions in dilute dichloromethane solutions has been investigated. The OH stretching vibration was used to monitor the hydrogen bonds formed between the anions and the methanol molecules, providing a direct measure of the hydrogen-bond strength. Concentrations of free and anionbonded methanol molecules were measured and the equilibrium constants calculated. The wavenumber shift and the free energy of hydrogen-bond formation was found to be significantly correlated. For the anions studied it was found that the hydrogen-bond strength increases in the order: PF6- 4- 4- 3CF3- 3- - -. Acta Chemica Scandinavica 1997.
- Kristiansson, Olof,Schuisky, Mikael
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p. 270 - 273
(2007/10/03)
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- Syntheses of the ruthenium(VI) alkyl complexes [Ru(N)R4-xClx]- (R = Me, CH2SiMe3) and the X-ray crystal structure of [N-n-Bu4][Ru(N)Me4]
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Anionic nitridoruthenium(VI) alkyl complexes [Ru(N)Me4]- and [Ru(N)(CH2SiMe3)4]- have been prepared by the alkylation of [Ru(N)(OSiMe3)4]- with AlMe3 or with Mg(CH2SiMe3)2, respectively. The structure of one of these, [N-n-Bu4][Ru(N)Me4], was determined by single-crystal X-ray diffraction: a = 9.359 (3) ?, b = 18.368 (4) ?, c = 15.193.(5) ?; V = 2519 (1) ?3; Z = 4; β = 105.31 (2)°; ρcalcd = 1.101 g/cm3, monoclinic space group P21/n. Mixed alkyl-chloro complexes, [Ru(N)R4-xClx]- (R = CH2SiMe3, x = 1-2; R = Me, x = 1-3), result from the reaction of HCl(g) with the alkyl complexes. The gold(I) chloro complex Au(PPh3)Cl reacts in a manner analogous to HCl and converts [Ru(N)Me4]- to [Ru(N)ClMe3]- with formation of Au(PPh3)Me. In contrast to the related osmium complexes, both Lewis acid adducts of the ruthenium nitrides and (alkylimido)tetraalkylruthenium complexes are thermally unstable.
- Shapley, Patricia A.,Kim, Hoon Sik,Wilson, Scott R.
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p. 928 - 933
(2008/10/08)
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