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1.
The bis(μ‐oxo)dicopper(III) species [CuIII2(μ‐O)2(m‐XYLMeAN)]2+ ( 1 ) promotes the electrophilic ortho‐hydroxylation–defluorination of 2‐fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η22‐O2)dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ‐oxo) unit. Ortho‐hydroxylation–defluorination occurs selectively in intramolecular competition with other ortho‐substituents such as chlorine or bromine.  相似文献   

2.
The reaction of the aromatic azo or imine compounds PhX=NR (X=N or CH; R = alkyl or aryl) and 2-(methylazo)propene, H2CC(CH3)N&.zdbnd;NCH3, with trans-IrCl(N2)(PPh3)2 yields the (ortho) metallated complexes IrHCl(G6H4X=NR)(PPh3)2 and IrHClCHC(CH3)-NNCH3](PPh3)2 respectively.The v(N=N) vibration in IrHCl(C6HZ4N=NPh)(PPh3)2 appears to be drastically lowered with respect to the free ligand vibration. Furthermore, Resonance Raman experiments show that this vibration is strongly coupled to both of the electronic transitions of this compound at longer wavelengths, which therefore must be closely connected with the azo group.1H and 13C NMR spectroscopic data and crystallographic studies of IrHCI(C6H4N=NPh)(PPh3)2 give strong evidence about the nature of the mechanism of these (ortho) metallation reactions.  相似文献   

3.
Oxidation of anisoles by acid bromate has been studied in acetic acid-water system in the presence of sulphuric acid. The reaction is first order each in [anisole] and [Br(V)]. The rate of reaction increased with increase in [H+] and percentage of acetic acid. The products of oxidation have been identified as ortho and para hydroxyanisoles. From the effect of [H+] and [acetic acid] on rate, H 2 + BrO3 has been established as the reactive species. Anisoles having electron-donating substituents in the benzene ring accelerate the rates and vice versa with a Hammett ρ value of −0.6. A mechanism involving the attack of H 2 + BrO3 on ortho/para position of the anisole in the rate-determining step has been proposed.  相似文献   

4.
Coherent anti-Stokes Raman scattering (CARS) has been used to observe H2 from H2CO + hv H2 + CO. Photolysis of K = 1 (ortho) lines of the 2141 S1 ← S0 transition produced no para-H2 (<4% statistical); and demonstrated nuclear spin conservation. H2 states v = 1, 2 and 3 were comparably populated.  相似文献   

5.
An ortho‐selective C? F bond borylation between N‐heterocycle‐substituted polyfluoroarenes and Bpin‐Bpin with simple and commercially available [Rh(cod)2]BF4 as a catalyst is now reported. The reaction proceeds under mild reaction conditions with high efficiency and broad substrate scope, even toward monofluoroarene, thus providing a facile access to a wide range of borylated fluoroarenes that are useful for photoelectronic materials. Preliminary mechanistic studies reveal that a RhIII/V catalytic cycle via a key intermediate rhodium(III) hydride complex [(H)RhIIILn(Bpin)] may be involved in the reaction.  相似文献   

6.
An ortho‐selective C F bond borylation between N‐heterocycle‐substituted polyfluoroarenes and Bpin‐Bpin with simple and commercially available [Rh(cod)2]BF4 as a catalyst is now reported. The reaction proceeds under mild reaction conditions with high efficiency and broad substrate scope, even toward monofluoroarene, thus providing a facile access to a wide range of borylated fluoroarenes that are useful for photoelectronic materials. Preliminary mechanistic studies reveal that a RhIII/V catalytic cycle via a key intermediate rhodium(III) hydride complex [(H)RhIIILn(Bpin)] may be involved in the reaction.  相似文献   

7.
The [3 + 2] cycloaddition (32CA) reactions of three nitrile oxides (NOs) (R‐CNO; R = Ph, CO2Me, and Br) with methyl acrylate (MA) have been theoretically studied within the molecular electron density theory. Topological analysis of the electron localization function of these NOs permits to establish that they will participate in zw‐type 32CA reactions. Analysis of the conceptual DFT indices indicates that these zw‐type 32CA reactions will have a low polar character as a consequence of the relatively low electrophilic character of MA and the low nucleophilic character of NOs, in agreement with the global electron density transfer computed at the corresponding TSs. The activation enthalpies associated with these 32CA reactions range from 8.2 to 12.7 kcal·mol?1. The presence of the bromide atom provokes the larger acceleration. While the 32CA reaction involving the CO2Me substituted NO is highly ortho regioselective, the other two reactions are poorly ortho regioselective. A bonding evolution theory study of the more favorable ortho regiosiomeric channel associated with the 32CA reaction involving the Br substituted NO indicates that this reaction is associated to a nonconcerted two‐stage one‐step mechanism, in which the activation energy is mainly related to the initial rupture of the C? N triple bond of the NO.  相似文献   

8.
H. Mager 《Tetrahedron》1981,37(3):509-521
In order to attain a better insight into the composition of Taft Eso, constants the rate data of hydrion catalysed esterification of both m,p-substituted and o-substiluted benzoic acids by cyclohexanol and methanol were submitted to a statistical analysis using inductive mesomeric and steric substituent constants and various dummy variables differently structured. Furthermore a principal component analysis with subsequent identification of the first principal component via multiple regression analysis was applied. It has been demonstrated that in the reactions of m,p substituted compounds some substituents capable of exerting strong mesomeric effects show peculiar characteristics deviating from the general trend. Since the same result was obtained in the correlations of ortho substituted benzoic acids this effect was taken into account using an appropriate dummy variable which in all cases improved the multiple coefficient of determination. It is concluded that the esterification rates of the ortho substituted compounds depend essentially upon inductive and steric effects (taken away OMe OEt and NO2) as proposed by Taft. While generally the Eso values may be regarded as some measure of a steric effect, this is not true for the methoxy and ethoxy groups.  相似文献   

9.
《Tetrahedron》2019,75(35):130473
An efficient CuI catalyzed intramolecular Ullmann-type C−N coupling reaction is described here. Newly substituted 1H-benzo[4,5]imidazo[1,2-a]pyrrolo[3,4-c]pyridine-1,3,5(2H, 11H)-trione has been easily synthesized from ortho halogenated N-substituted pyrrolo[3,4-c]pyridine-1,3,6(5H)-triones in presence of CuI catalyst and K2CO3 base without any ligand. This procedure is based on intramolecular Ullmann-type reaction and provides a proficient method of making fused tetracyclic heterocycles.  相似文献   

10.
Radiation chemical reactions ofOH, O•−, N3 and e aq t- witho- and m-hydroxycinnamic acids were studied. The second-orderrateconstantsforthereaction ofOH with ortho and meta isomers in buffer solution at pH7 are 3.9±0.2 × 109 and 4.4 ± 0.3 × 109 dm3 mol-1 s-1 respectively. At pH 3 the rate with the ortho isomer was halved (1.6 ± 0.4 × 109 dm3 mol-1 s-1) but it was unaffected in the case of meta isomer (k = 4.2±0.6 × 109dm3mol-1 s-1). The rate constant in the reaction of N3 with the ortho isomer is lower by an order of magnitude (k = 4.9 ± 0.4 × 108 dm3 mol-1s-1). The rates of the reaction of e aq t- with ortho and meta isomers were found to be diffusion controlled. The transient absorption spectrum measured in theOH witho-hydroxycinnamic acid exhibited an absorption maximum at 360 nm and in meta isomer the spectrum was blue-shifted (330 nm) with a shoulder at 390 nm. A peak at 420 nm was observed in the reaction of Obb−with theo-isomer whereas the meta isomer has a maximum at 390 and a broad shoulder at 450 nm. In the reaction of the absorption peaks were centred at 370–380 nm in both the isomers. The underlying reaction mechanism is discussed.  相似文献   

11.
The present work provides quantitative results for the rate of unimolecular carbon-hydrogen bond fission reaction of benzene and nitro benzene at elevated temperatures up to 2000 K. The potential energy surface for each C-H (in the ortho, meta, and para sites) bond fission reaction of nitro benzene was investigated by ab initio calculations. The geometry and vibrational frequencies of the species involved in this process were optimized at the MP2 level of theory, using the cc-pvdz basis set. Since C-H bond fission channel is barrier less reaction, we have used variational RRKM theory to predict rate constants. By means of calculated rate constant at the different temperatures, the activation energy and exponential factor were determined. The Arrhenius expression for C-H bond fission reaction of nitro benzene on the ortho, meta and para sites are k(T) = 2.1 × 1017exp(?56575.98/T), k(T) = 2.1 × 1017exp(?57587.45/T), and k(T) = 3.3 × 1016exp(?57594.79/T) respectively. The Arrhenius expression for C-H bond fission reaction of benzene is k(T) = 2 × 1018exp(?59343.48.18/T). The effect of NO2 group, location of hydrogen atoms on the substituted benzene ring, reaction degeneracy, benzene ring resonance and tunneling effect on the rate expression have been discussed.  相似文献   

12.
The reduction of copper (II) chloride by molybdenum and rhenium biscyclopentadienyl hydrides upon their interaction in donor-type solvents has been studied by NMR, X-ray diffraction, and magnetic methods. It is established that the ionic complex [(η5-C5H5)2Re]+[CuCl2]? forms ortho rhombic crystals with a - 13.696(2) Å, b = 7.317(1) Å, c = 5.969(1) Å, space group Pm21n, Z = 2. The cyclopentadienyl rings make a bent-sandwich with an angle between the ring centres and Re atom of 150.1°; the ClCuCl angle being 174.8° and the ReCu minimum distance 4.346(29) Å. The solution of [(η5-C5H5)2Re]+ [CuCl2]? seems to activate the CH bond of the C5H5 rings, which results in the addition of the [(C5H5)(C5H4)ReH]+ hydride ion.  相似文献   

13.
The structure and rotational barrier for the mesityl-silicon bond of 2,2-dimesityl-1,1,1,3,3,3-hexamethyltrisilane have been investigated by 1H- and 13C-variable temperature nuclear magnetic resonance (NMR) as well as by density functional theory structural calculations. The calculations show that the lowest energy structure has C2 symmetry with nonequivalent ortho methyl groups, consistent with the crystal structure and solution NMR. The nonequivalent ortho methyl groups exchange through a Cs transition state with a calculated relative free energy of 11.0 kcal mol−1. The barrier for this rotation found by dynamic NMR is 13.4 ± 0.2 kcal mol−1 at 298 K.  相似文献   

14.
The reaction of ortho‐mercurated anilines with benzaldehyde gave the ortho‐mercurated Schiff bases. The reaction of the mercurated Schiff bases with tellurium tetrabromide in 1:1 and 2:1 mole ratio using dry chloroform as solvent gave the ortho‐tellurated Schiff bases compounds ArTeBr3 and Ar2TeBr2, respectively, in good yields (where Ar = 5‐ClC6H3N=CHC6H5, 5‐BrC6H3N=CHC6H5, 5‐CH3OC6H3N=CHC6H5, and 5‐NO2C6H3N=CHC6H5). The reduction of ArTeBr3 by hydrazine hydrate gave the corresponding ditelluride (i.e., Ar2Te2). Treatment of Ar2TeBr2 with hydrazine hydrate afforded tellurides (Ar2Te) in good yields. Attempts to prepare the corresponding aryl tellurenyl bromides, ArTeBr, by partial reduction of ArTeBr3 with various reducing agents were unsuccessful. All these new compounds were characterized by microanalysis, 1H, and 13C NMR, IR, and mass spectroscopic data. A computational study for the Te → N interactions of all compounds was calculated using the GAUSSIAN 03 program package. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:307–315, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20437  相似文献   

15.
Adsorption and diffusion of ortho, meta, and para cis hydrogen dimers, on central and edge rings of coronene (nanographene), were studied by using the DFT-D method, considering different multiplicities. Calculated values of adsorption energy, coadsorption energy, diffusion barriers, and reaction barriers for the H2 formation (Langmuir-Hinshelwood (LH) mechanism) were evaluated for ortho and para locations. The adsorption of an H atom increases the adsorption energy of another hydrogen (coadsorption). The most stable dimers are those where an H is adsorbed on hydrogenated-edge sites. Dimers with multiplicity M = 1, with H separated by an odd number of bonds, have higher coadsorption energies (higher diffusion barriers) than those where the separation is by an even number. The H2 formation is more feasible on edge-edge and edge-center sites; however, on ortho hydrogenated-edge sites, it is not energetically favored. For M = 3, H2 formation is not observed because desorption of H occurs.  相似文献   

16.
The reaction of O2(1Δg) with HO2(X?) was studied in an isothermal flow reactor in the pressure range 7?p? 10.7 mbar at temperatures between 299?T? 423 K. H-atom production was observed in the reaction O2(1Δg) + HO22A′) - H(2S)+ 2O2 (3Σg?). The rate of this reaction (k1) is estimated to be k1 = (1 ± 0.5) × 1014 CM3 Mol?1 s?1. The implications of this reaction to recent determinations of the rate of the reaction H + O2(1Δg) are discussed.  相似文献   

17.
In methanol, the reaction of Ti(OiPr)4, N-(2-hydroxyphenyl)salicylideneimine (H2Sap) and 8-hydroxyquinoline (HQ) in stoichiometric ratio 1:1:x yielded Ti(Sap)2 precipitate as initial product even when x was as high as 10. However, when the reaction mixture with x = 2 was left standing for 12 h or more, a small amount of red crystalline Ti(Sap)Q(OMe) was isolated. Addition of wet acetonitrile to the reaction mixture with x = 10, small amount of another red crystalline [Ti(Sap)Q]2(μ-O) was obtained after standing for 2 days. The reaction between TiQ2(OiPr)2 and H2Sap in methanol with stoichiometric ratio of y:1 also yielded Ti(Sap)2 as initial product even for y as large as 10. 1H NMR investigation of the reaction of TiQ2(OMe)2 with H2Sap revealed that Ti(Sap)Q(OMe) was not detected initially. These experimental results can be explained based on a mechanism that includes: (i) rapid reaction of H2Sap with Ti(IV) centers to form Ti(Sap)2; (ii) equilibrium between TiQ2(OMe)2 and Ti(Sap)Q(OMe); (iii) equilibrium between Ti(Sap)Q(OR) and Ti(Sap)2; and (iv) limited solubilities of Ti(Sap)Q(OR) and Ti(Sap)2. The equilibrium constants and solubilities in the mechanism were determined by the 1H NMR spectral method. The structures of Ti(Sap)Q(OMe) and [Ti(Sap)Q]2(μ-O), consisting octahedrally coordinated Ti(IV), were determined by X-ray diffraction method.  相似文献   

18.
Selenoureas are obtained by a novel three-component condensation reaction from metallic selenium, triethyl orthoformate and a primary or secondary amine. The reaction is carried out as solvent-free one pot-procedure at 180-190°C under inert gas with a reaction time of 8 h. The reaction was tested for piperidine, isopropylamine, N,N′-dimethylpropylenediamine (Me-NH-CH2-CH2-CH2-NH-Me) and N,N′-disubstituted ethylenediamines (R-NH-CH2-CH2-NH-R, R=Me, Et, iPr, tBu, Ph).  相似文献   

19.
Ointment-like poly(ortho esters) were synthesized for the first time from the reaction of 3,9-bis(methylene)-2,4,8,10-tetraoxaspiro[5. 5] undecane with poly(ethylene glycol)-400, N,N-bis(2-hydroxyethyl)-n-hexadecylamine and N,N-bis(2-hydroxyethyl) palmitamide, respectively. The obtained polymers were characterized by 1H NMR spectra, 13C NMR spectra, elemental analyses, light scattering, and measurements of intrinsic viscosity. The influence of catalyst on the intrinsic viscosity of polymers was investigated. The 9-[(1,3-dihydroxy-2-propoxy) methyl] guanine controlled release profiles of hydrophobic ointment-like polymers such as polymer PII in vitro were also discussed.  相似文献   

20.
We developed a hydrodehalogenation reaction of polyhaloalkanes catalyzed by paddlewheel dimolybdenum complexes in combination with 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) as a non-toxic H-atom source as well as a salt-free reductant. A mixed-ligated dimolybdenum complex Mo2(OAc)2[CH(NAr)2]2 (3a, Ar = 4-MeOC6H4) having two acetates and two amidinates exhibited high catalytic activity in the presence of nBu4NCl, in which [nBu4N]2[Mo2{CH(NAr)2}2Cl4] (9a), derived by treating 3a with ClSiMe3 and nBu4NCl, was generated as a catalytically-active species in the hydrodehalogenation. All reaction processes, oxidation and reduction of the dimolybdenum complex, were clarified by control experiments, and the oxidized product, [nBu4N][Mo2{CH(NAr)2}2Cl4] (10a), was characterized by EPR and X-ray diffraction studies. Kinetic analysis of the hydrodehalogenation reaction as well as a deuterium-labelling experiment using MBTCD-d8 suggested that the H-abstraction was the rate-determining step for the catalytic reaction.  相似文献   

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