Synthesis,kinetics and mechanism of the reaction of a quasi‐aromatic copper(II) complex, [Cu(PnAO)‐6H]0, with aromatic aldehydes

The quasi‐aromatic metal complex (1,1,2,8,9,9‐hexamethyl‐4,6‐dioxa‐5‐hydro‐3,7,10,14‐tetraazacyclotetradecane‐2,7,10,12‐tetraene)copper(II), [Cu(PnAO)‐6H]⁰ (AH), was synthesized. Reactions of AH were studied spectrophotometrically in acidic media (pH = 1 ∼ 2, EtOH:H₂O = 1:4 v/v) with para‐substituted benzaldehydes (ald). The Cu,2N,3C quasi‐aromatic heterocyclic ring in AH is highly reactive at the central‐aromatic‐carbon atom, C12, to most aldehydes. A novel parallel, competitive and consecutive second‐order reaction mechanism is proposed. To obtain the rate constants following this mechanism, the Gauss‐Newton‐Marquardt and Runge‐Kutta methods were employed. Consistent results were obtained. Effects of acidity, solvent, temperature and substituent R (RH, CH₃, OCH₃, Cl) of the aromatic aldehydes on the reaction rate constants were studied. The results support the proposed SN2 mechanism. A linear free energy relationship between the rate constant k₁ and the Hammett parameters for the substituted benzaldehydes as well the activation parameters are presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 1–8, 2001     

Structure of the copper(II) complex of 2-acetylpyridine hexamethyleneiminylthiosemicarbazone, [Cu(Lhexim)Br]

Summary An anion (loss of ³N hydrogen) of a 2-acetylpyridine azacyclothiosemicarbazone coordinates in a planar conformation to the central Cu atom through the pyridyl N, azomethine N and thiolato S atoms. The interatomic distances are Cu{ie449-01}N = 2.016(6), Cu{ie449-02}N = 1.963(5) and Cu{ie449-03}S = 2.236(3) Å, respectively, with the fourth co-ordination site occupied by a bromine atom, Cu{ie449-04}Br = 2.359(2) Å.     

类芳香金属配合物-[Ni(PnAO)-6H]~0的生成反应动力学及机理研究

用紫外可见光谱法研究了在碱性溶液中[Ni(PnAO)-H]~++H_2O_2→[Ni(PnAO)-6H]~0的反应动力学并提出了包含自由基·OH的复杂反应机理。采用经典确定反应机理的方法及Gauss-Newton-Marquardt非线性拟合和Runge-Kutta解一次微分方程组程序处理数据并获得了良好的结果。改变碱浓度及双氧水浓度所得结果支持所拟机理。     

Kinetics and mechanism of base-catalyzed hydrolysis of Cu(II)-malonamide complex

A kinetic study of base-catalyzed hydrolysis of Cu(II)-malonamide complex has been performed in sodium hydroxide solution (0.2–1.25M). The reaction follows an irreversible first-order consecutive path: The variation of k_1obs and k_2obs with alkali concentration was found to be in good agreement with the equations: where B₁, B₂, C₁, and C₂ are empirical constants. The mechanism of hydrolysis of Cu(II)-malonamide complex has been discussed and rate equations have been derived. Retardation of rate of hydrolysis due to coordination of Cu(II) with malonamide, in alkaline medium, has been explained in terms of comparatively slow breakdown of the C? N bond of the tetrahedral intermediate (TI). Thermodynamic parameters have also been evaluated.     

Kinetics and mechanism of the stepwise complex formation of Cu(II) with tren-centered tris-macrocycles

The stepwise complexation kinetics of Cu2+ with three tetratopic ligands L1, L2 and L3, tren-centred macrocycles with different bridges connecting the 14-membered macrocycles with the tren unit, have been measured by stopped-flow photodiode array techniques at 25 degrees C, I= 0.5 M (KNO3), and pH = 4.96. The reaction between the first Cu2+ and the ligand consists of several steps. In a rapid reaction Cu2+ first binds to the flexible and more reactive tren-unit. In this intermediate a translocation from the tren unit to the macrocyclic ring, which forms the thermodynamic more stable complex, takes place. This species can react further with a second Cu2+ to give a heterotopic dinuclear species with one Cu2+ bound by the tren-unit and the other coordinated by the macrocycle. A further translocation occurs to give the homoditopic species with two Cu2+ in the macrocycles. Finally a slow rearrangement of the dinuclear complex gives the final species. The rates of the translocation are dependent on the length and rigidity of the bridge, whereas the complexation rates with the tren unit are little affected by it. VIS spectra of the species obtained by fitting the kinetic results, EPR-spectra taken during the reaction, and ES mass spectra of the products confirm the proposed mechanism. The addition of a second, third and fourth equivalent of Cu2+ proceeds in an analogous way, but is complicated by the fact that we start and end with a mixture of species. These steps were evaluated in a qualitative way only.     

Kinetics and mechanism of base-catalyzed hydrolysis of Cu(II)-salicylamide complex

The kinetics of hydrolysis of Cu(II)-salicylamide complex have been studied in sodium hydroxide solution (0.5 to 2.5M). The observed pseudo-first-order rate constants vary according to the empirical equation 1/??_obs = B₁ + B₂/[ōH] up to 2.0 M sodium hydroxide concentration. The mechanism of base-catalyzed hydrolysis has been proposed and it is concluded that the reaction proceeds by the interaction of complex with the nucleophile, forming tetrahedral intermediate which then breaks down to products. The rate equation has been derived. Thermodynamic parameters have also been reported.     

Kinetics and mechanism of exchange reaction of [Y(APTA)] (APTA=o-aminophenol-N,N, O-triacetic acid) with copper(II)

Summary The kinetics of the exchange reaction between [Y(APTA)] and Cu^II have been investigated over a range of [H⁺] from 2.5×10^–5 to 7.5×10^–4 mol dm^–3 at 30°C and ionic strength 0.2 mol dm^–3 KNO₃. The results show that the exchange reaction proceeds via both self-and proton-catalyzed dissociation of [Y(APTA)] and also by the direct attack of Cu^II on [Y(APTA)]. The corresponding rate constants k_d, k _h and k_Cu have been evaluated as 6.3s^–1, 8.4×10⁴ mol^–1 dm³ s^–1 and 416mol^–3 dm³ s^–1 respectively. The possible intermediates are discussed in terms of the structure of APTA. The complex-formation rate constants of Y^III with APTA^3- and HAPTA^2- were also obtained.     

Cu(II)氧化抗坏血酸的动力学和机理

本文在总离子强度I=1.00mol.dm^-^3、[Cu^2^+]>>[H2A]、[H^+]>>[H2A]、无氧及无缓冲剂存在的条件下, 研究Cu(II)氧化抗坏血酸(H2A)的动力学和机理. 发现Cu(II)与H2A不发生配位反应, 但以Cl^-存在的情况下, 确有Cu(II)的H2A配合物生成, Cu(II)氧化H2A反应的速率方程为r={a+b[Cl^-]}[Cu^2^+]{[H+]+Ka}^-^2, 25℃时a和b值分别为4.08×10^-^4s^-^1和0.555dm^3.s^-^1.mol^-^1. Cu(II)氧化H2A反应的表观活化能为68.1KJ.mol^-^1. 根据动力学结果, 提出了反应机理, 并给出了配合物ClCuHA的结构形式.     

Kinetics and mechanism of the reduction of 1,10-phenanthroline—copper(II) complex

The cyclic voltammetric study of 1,10-phenanthroline—copper(II) complex was carried out in acidic buffer solution. It was found from the current—mole ratio (copper (II): 1,10-phenanthroline) relationship that the maximum coordination number of 1,10-phenanthroline—copper(II) complex was four under the present experimental condition. The reduction mechanism and kinetics of copper(II) was studied in the presence of various concentrations of 1,10-phenanthroline.     

A dinuclear diamagnetic copper(II) complex [Cu2(ophen)2]Cl2 with hydroxylated phen

A dinuclear diamagnetic copper(II) complex, [Cu₂(ophen)₂]Cl₂ (Hophen = 2-hydroxy-1,10-phenanthroline), has been synthesized and characterized, providing good structural evidence for the long-debated Gillard mechanism.     

Molecular structure of the dimeric complex of copper (II) chloride with triphenyl-N-[6-methylpyridyl-2]phosphinimine

The complex of copper(II) dichloride with triphenyl-N-(6-methylpyridyl-2)phosphinimine has been studied by X-ray diffraction. This compound has a dimeric structure with two ₂-bridge chlorine atoms. The coordination of copper atoms by three chlorine atoms and the N atom of the heterocycle is of a strongly distorted planar-square type. A peculiar feature of this structure is the presence of intramolecular contacts Cu...N (2.504 Å and 2.492 Å) involving the imine nitrogens of the P,N-containing ligands which are responsible for strong additional coordination of the copper atoms. In methanol the P,N-containing ligand forms a complex with Cu(II) where the metal-to-ligand ratio is equal to 12. The ESR data point to the bidentate nature of the ligand in solution, where all four nitrogen atoms, contributed by both of the ligands, are located in the plane of the metal atom.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 337–341, February, 1993.     

Determination of copper(I)-ethylene complexes, [Cu(C2H4)]+ and [Cu(C2H4)2]+, with aid of EDTA titration of copper(I) and copper(II) ions

Summary Volumetric measurements of ethylene and simple EDTA titration of copper(I) and copper(II) ions confirm that [CuL]⁺ and [CuL₂]⁺ are formed when an aqueous solution of copper(II) is reduced by copper metal in the presence of ethylene, (L). The formation constants,K ₁=[CuL⁺]²[Cu²⁺]^–1[L]^–2 andK ₂=[CuL ₂ ⁺ ]^–1[L]^–1, have been estimated. The formation of [CuL]⁺ is accompanied by an enthalpy change, H, of –25 kJ mol^–1, and a positive entropy change, S, of 13 J mol^–1 K^–1.     

Crystal structure of bis(l-arginine)copper(II) hexachlorodimercurate, [Cu(l-Arg)2]Hg2Cl6

By means of X-ray diffraction the chain structure of [Cu(l-Arg)₂]Hg₂Cl₆ (monoclinic, a = 10.2348(9) Å, b = 9.1386(7) Å, c = 14.8521(14) Å, β = 97.455(11)°, space group P2₁) is established. The chains are formed by square-planar [Cu(l-Arg)₂]²⁺ cations of the type trans-[Cu(N)₂(O)₂] (l-Arg is the zwitter-ion of arginine; Cu-N 1.992 Å and 1.938(6) Å, Cu-O 1.953 Å and 1.967(4) Å) that are bonded to two adjacent binuclear [Cl₂Hg(μ-Cl)₂HgCl₂]^2? ions through its clorine atoms Cl (Hg-Cl bonds are within 2.34–2.78 Å). With these two additional Cu…Cl contacts Cu adopts the geometry of an elongated octahedron with two apical Cl (Cu-Cl 2.961 Å and 3.064(3) Å).