Selective copper(II)-catalyzed aerobic oxidative cleavage of aromatic gem-disubstituted alkenes to carbonyl compounds under neutral and mild conditions

Three copper(II) catalytic systems, CuCl₂·2H₂O, CuCl₂·2H₂O+phenanthroline, and [Cu(μ-Cl)Cl(phen)]₂ were used to cleave alkenes to their corresponding carbonyl compounds under aerobic and neutral conditions. [Cu(μ-Cl)Cl(phen)]₂ shows enhanced selectivity over the other two catalytic systems. The oxidative cleavage reactions were carried out in mixed H₂O/THF solvent system under oxygen (4 atm) at 60°C. The real oxidant is 2-hydroperoxytetrahydrofuran, which is generated in situ in the process through the reaction between THF and oxygen catalyzed by copper(II). The cleavage reactions are selective for aromatic gem-disubstituted alkenes. Aromatic internal alkenes are slow to be oxidized, and both aliphatic terminal and internal alkenes are inert to oxidative cleavage. Free radical scavenger 2,2,6,6, tetramethylpiperidinyl-1-oxyl (TEMPO) deactivates the reaction indicating the involvement of free radical path in the reaction mechanism.     

Rapid cleavage of unactivated, unstrained amide bonds at neutral pH

Building upon the discovery of Suggs and Pires that N-(2-hydroxyethyl)glycine amides undergo rapid amide cleavage under mild conditions [ Suggs, J. W. ; Pires, R. M. Tetrahedron Lett. 1997, 38, 2227-2230 ], we synthesized the derivatives (4aalpha,8beta,8aalpha)-1-ethylamido-8-hydroxydecahydroquinoline ( 4) and (4aalpha,8alpha,8abeta)-1-ethylamido-8-hydroxydecahydroquinoline ( 5). These two species are conformationally constrained, but steric compression is not introduced between the hydroxyl group and the amide functionality it attacks. At 20 degrees C and slightly basic pH, derivatives 4 and 5 undergo amide cleavage with half-lives of 21 min and 14 h, respectively, which correspond to rate increases of 251- and 6.3-fold relative to the acyclic analogue N-(2-hydroxyethyl)glycine amide ( 3).     

Isomerism of copper(II) coordination compounds with hydroxamic acids

The structure of Cu^II complexes with hydroxamic acids Cu[R¹N(O)−(O)CR²]₂, where R¹=Ph, R²=Me; R¹=Me, R²=Ph, was studied by ESR spectroscopy. In toluene solutions and low-temperature glasses, the complexes exist as two forms, which were identified ascis-andtrans-isomers. The proportions of the isomers were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 726–729, April, 1999.     

Synthesis of copper(II) coordination compounds with benzoxazine derivatives

Copper(II) complexes with 1,2-dihydro-4H-3,1-benzoxazine (HL) derivatives, CuLOH, were prepared by anodic electrosynthesis. The use of an amalgamated copper anode resulted in an increase in the electrosynthesis rate. It follows from the IR spectra of the products that the benzoxazine ring in the ligand molecule is opened upon complexation, while a six-membered chelate ring involving the oxygen atom of the deprotonated phenol group and the imine nitrogen atom is formed.     

Potential-modulated DNA cleavage by (N-salicylideneglycinato)copper(II) complex.

The interaction of aqua (N-salicylideneglycinato)copper(II) (Cu(salgly)2+) complex with calf thymus DNA has been investigated by cyclic voltammetry. Potential-modulated DNA cleavage in the presence of Cu(salgly)2+ complex was performed at a gold electrode in a thin layer cell. DNA can be efficiently cleaved by electrochemically reducing Cu(salgly)2+ complex to Cu(salgly)+ complex at -0.7 V (vs. Ag/AgCl). When the solution was aerated with a small flow of O2 during electrolysis, the extent of DNA cleavage was dramatically enhanced, and hydroxyl radical scavengers inhibited DNA cleavage. These results suggested that O2 and hydroxyl radical were involved in potential-modulated DNA cleavage reaction. The percentage of DNA cleavage was enhanced as the working potential was shifted to more negative values and the electrolysis time was increased. It was also dependent on the ratio of Cu(salgly)2+ complex to DNA concentration. The cleaved DNA fragments were separated by high performance liquid chromatography (HPLC). The experimental results indicated that the method for potential-modulated DNA cleavage by Cu(salgly)2+ complex was simple and efficient.     

Equilibrium studies of beta-diketoaryl azo compounds with cobalt(II), nickel(II) and copper(II)

The interactions of some beta-diketoaryl azo substituted compounds with Co(II), Ni(II) and Cu(II) are discussed. The non-protonated form of the ligand is the main complexing species. The stability constants have been evaluated. The effect of substituent groups on the complexing ability of the ligands is discussed.     

Isomers of α-amino acids with copper(II). Part VI. Novel equilibria at high pH in copper(II):Amino-acid solutions

Summary Circular dichroism spectra show the presence at high pH of a new pH-dependent equilibrium for aqueous solutions of amino-acid with copper(II) ions. Measurements are interpreted in terms of an apparent acid dissociation constant. A typical value for pK_a is 12.17 for alanine. Electron spin resonance and circular dichroism suggest that the high pH form is a monomeric hydroxobisalaninato-complex of copper(II).Part V. see Ref. 1.     

On the structure of copper(II) coordination compounds with L-histidine

Quantum chemical calculations are performed for the spatial and electron structure of complex compounds of L-histidine and its ionized forms with copper(II) for a variety of compositions within the density functional theory (DFT) using the B3LYP functional and 6-311G(d) basis. The solvent (water) is considered within the PCM approximation. EPR spectroscopy is used to study the equilibrium in the copper(II)–L-histidine system in an aqueous solution at рН 2–11. A comparison between the theoretical calculations and the EPR spectra suggests the following geometry for the coordination environment of the copper(II) ion in the complex compounds: CuHLL–square-planar coordination; CuL₂, CuHLL′, and CuLL′–distorted square pyramid; and CuL₂′–octahedral environment.     

Absorption and fluorescence behavior of cytosine irradiated at different pH and in the presence of Cu(II) ions at neutral pH

Dilute aqueous solutions of cytosine were irradiated with⁶⁰Co -rays under N₂O saturated conditions at different pH and in the presence of Cu(II) ions at neutral pH. The base degradation decreased from neutral to acidic and basic conditions. In the presence of metal ions at neutral pH conditions there was a significant increase in the base degradation compared to that in the absence of metal ions under similar conditions. From the difference absorption spectra and fluorescence behavior of the irradiated solutions it was observed that the major radiolytic products of cytosine under different conditions are cytosine glycols, 5-hydroxycytosine, hydroxy-hydrocytosine and cytosine dimers. The yields of dimers is maximum in neutral conditions and it decreased from basic to acidic conditions. However, in the presence of Cu(II) ions formation of cytosine dimers is completely restricted and there is an increase in the yields of cytosine glycol, hydroxy-hydrocytosine and 5-hydroxycytosine. From the post-radiolytic changes in absorption and fluorescence behavior of irradiated solutions, it is revealed that some of the radiolytic products, namely cytosine glycol and hydroxy-hydrocytosine decompose to 5-hydroxycytosine and cytosine, respectively.     

Delocalization of unpaired electron in copper(II) complexes with azo compounds

Conclusions Contact interaction of the unpaired electron of the copper atom with the two equivalent nitrogen atoms, attached directly to the copper atom, is accomplished in the inner complexes of copper(II) with bis(benzeneazo-p-cresol) derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2771–2773, December, 1973.The authors thank B. I. Stepanov for the supplied compounds.     

Preparation and study of bis(theophyllinato) copper(II) compounds

Bis(theophyllinato) copper(II) dihydrate and its anhydrous form, were prepared. Their thermal, spectral and magnetic behaviours were investigated. Magnetic susceptibility studies show that the dihydrate form can be fitted to the Curie law. The magnetic behaviour of the anhydrous form is interpreted in terms of antiferromangetically exchange-coupled pairs of copper atoms. The change in magnetic properties as the dihydrate is dehydrated implies that structural rearrangement in first coordination sphere of copper accompanies the dehydration process. For bis(theophyllinato)copper(II) dihydrate we propose a pseudo octahedral coordination of copper(II) in a polymeric chain, and for the anhydrous form four-coordination in binuclear units.     

Efficient plasmid DNA cleavage by a mononuclear copper(II) complex

The Cu(II) complex of the ligand all-cis-2,4,6-triamino-1,3,5-trihydroxycyclohexane (TACI) is a very efficient catalyst of the cleavage of plasmid DNA in the absence of any added cofactor. The maximum rate of degradation of the supercoiled plasmid DNA form, obtained at pH 8.1 and 37 degrees C, in the presence of 48 microM TACI.Cu(II), is 2.3 x 10(-3) s(-1), corresponding to a half-life time of only 5 min for the cleavage of form I (supercoiled) to form II (relaxed circular). The dependence of the rate of plasmid DNA cleavage from the TACI.Cu(II) complex concentration follows an unusual and very narrow bell-like profile, which suggests an high DNA affinity of the complexes but also a great tendency to form unreactive dimers. The reactivity of the TACI.Cu(II) complexes is not affected by the presence of several scavengers for reactive oxygen species or when measured under anaerobic conditions. Moreover, no degradation of the radical reporter Rhodamine B is observed in the presence of such complexes. These results are consistent with the operation of a prevailing hydrolytic pathway under the normal conditions used, although the failure to obtain enzymatic religation of the linearized DNA does not allow one to rule out the occurrence of a nonhydrolytic oxygen-independent cleavage. A concurrent oxidative mechanism becomes competitive upon addition of reductants or in the presence of high levels of molecular oxygen: under such conditions, in fact, a remarkable increase in the rate of DNA cleavage is observed.     

Complex compounds of 1,5-disubstituted 2,4-dithiobiurets with copper(II) chloride

1,5-diphenyl, 1,5-di-p-tolyl, 1-phenyl 5-0-tolyl, 1-phenyl 5-p-tolyl and 1-methyl 5-p-tolyl 2,4-dithiobiurets react with anhydrous copper(II) chloride in alcohol to form golden yellow complexes of general formula [CuL₂]· Cl₂, where L is a molecule of the ligand. The structures of these complexes have been studied by infrared spectroscopy, conductance and magnetic susceptibility measurements. The unusual magnetic moment (1.11–1.34 B.M.) values of these complexes are indicative of the metal–metal bonding. The structure of these complexes are proposed to have square planer configurations.     

Zinc organic compounds of some oximes coordinated with nickel(II), palladium(II) and copper(II) ions

Coordinated oximes with nickel(II), palladium(II) and copper(II) ions proved capable of giving substitution reactions with a series of zinc organic compounds. Studies have revealed that, in the cases of dimethylglyoxime and salicylaldoxime, the reaction products result from substitution of the O? H···O hydrogen bridges existing in such compounds by O? Zn? O bridges. All compounds reported in this paper were separated as colored powders and characterized by elemental analyses, IR spectroscopy, X‐ray diffraction and magnetic measurements. The new zinc organic compounds form amine adducts. Among the amine adducts, only those with pyridine were isolated and characterized. Copyright © 2001 John Wiley & Sons, Ltd.     

An EPR study of various compounds of copper (II) and silver (II)

The electron paramagnetic resonance (EPR) spectra in the three-centimeter and decimeter wavelength ranges have been studied in liquid and frozen solutions of copper(II) and silver(II) in ortho-, pyro-, and metaphosphoric acids, sulfuric acid, and nitric acid, and also in liquid and frozen solutions of Cu(II) in fluorosilicic acid. The parameters of the spin Hamiltonian have been determined. It has been shown that the magnetic ion M(II) in these compounds is situated in an axially distorted octahedron, formed by six oxygen atoms. The EPR spectra of frozen solutions of M(II) in ortho-, pyro-, and metaphosphoric acids, obtained by the procedure described in the present paper, do not differ from one another. Study of the EPR spectra over a wide range of frequencies has shown that for the Cu(II) compounds the condition of strong fields is satisfied as far as 800–1000 MHz, but on going to lower frequencies the condition of intermediate fields is satisfied. For the Ag(II) compounds the condition of strong fields is satisfied throughout the entire range of frequencies studied. It can be seen from the experimental results obtained that the values of the anisotropic hyperfine splitting (HFS) constants, reduced to unit magnetic moment of the corresponding nuclei, increase on going from the Cu(II) ions with n=3 to the Ag(II) ions with larger principal quantum number (n=4).In conclusion the authors thank B. M. Kozyrev for extensive discussion of the results and L. F. Shatrukov for assistance with the calculation of the spectra on the electronic computer.