Gábor Speier

Copper-catalysed oxidation of catechols by dioxygen

Abstract The catalytic activity of chloro(pyridine)copper(I) in the oxidation of 3,5-di-t-butylcatechol in dichloromethane and chloroform by dioxygen was studied kinetically. The reaction is quantitative and the overall rate equation shows second-order in the catalyst, first-order in the dioxygen and zero-order in the catechol concentrations, the rate-determining step being the formation of a dinuclear peroxo complex from the superoxo copper(I) species. The reaction can be used for the preparation of 3,5-di-t-butyl-o-benzoquinone. 4-t-Butylcatechol, 3,5-diisopropylcatechol, 9,10-dihydroxyphenanthrene and 3,5-dicyclohexylcatechol could be also oxidized to the corresponding quinones. No ring cleavage occurred as found with copper(I) chloride in pyridine solvent.

Kinetics and mechanism of the Cu(I) and Cu(II) flavonolate-catalyzed oxygenation of flavonol. Functional quercetin 2,3-dioxygenase models

Abstract The oxygenation of flavonol (flaH) using Cu II (fla) 2 and Cu I (fla)(PPh 3 ) 2 catalysts results in oxidative cleavage of the heterocyclic ring to give O -benzoylsalicylic acid ( O -bsH) and CO as primary products. The oxygenolysis of flavonol catalyzed by Cu II (fla) 2 in DMF was followed by electronic spectroscopy and the rate law was found to be −d[flaH]/d t = k obs [flaH][Cu II (fla) 2 ][O 2 ]. The rate constant, activation energy, activation enthalpy and entropy at 393 K are as follows: k obs /s −1 mol −2 dm −6 =(2.02±0.07)×10 3 , E a /kJ mol −1 =142±6, Δ H ‡ /kJ mol −1 =139±5, and Δ S ‡ /J mol −1 K −1 =168±13. The results of the kinetic measurements of the Cu I (fla)(PPh 3 ) 2 -catalyzed oxygenation shows that in the presence of a large excess of the substrate, the Cu I (fla)(PPh 3 ) 2 reacts with flavonol in an irreversible step to Cu II (fla) 2 , and, then, the mechanism of the oxygenation is the same as that with the Cu II (fla) 2 -catalyzed reaction.

Synthesis and characterization of copper(I) and copper(II) flavonolate complexes with phthalazine ligand, and their oxygenation and relevance to quercetinase

Abstract Copper(I) and copper(II) flavonolate (fla) complexes with 1,4-(di-2′-pyridyl)aminophthalazine ligand (PAPH 2 ) have been prepared by the reaction of copper salts with flavonol and the ligand in acetonitrile or dichloromethane. The copper(II) centers are bound to the tetradentate phthalazine ligand resulting in both mononuclear and binuclear complexes. Flavonol is oxygenated to the corresponding depside catalyzed by flavonolato copper(II) phthalazine complexes.

One metal–two pathways to the carboxylate-enhanced, iron-containing quercetinase mimics

Mononuclear iron(iii) flavonolate was synthesized as synthetic enzyme-substrate complex, and its direct and carboxylate-enhanced dioxygenation as biomimetic functional models with relevance to flavonol 2,4-dioxygenase are briefly described.

The kinetics and mechanism of homogeneous hydrogen transfer from alcohols to benzylideneacetone catalyzed by dichlorotris(triphenylphosphine)ruthenium(II)

Abstract Dichlorotris(triphenylphosphine)ruthenium(II) catalyzes the hydrogen transfer from alcohols to olefins. Kinetic studies were carried out at 170–190°C using the ruthenium(II) complex as homogeneous catalyst, benzyl alcohol, diphenylcarbinol, methylphenylcarbinol and benzoin as the hydrogen donors, benzylideneacetone as the hydrogen acceptor, and dibenzyl ether as a solvent. The IR spectra and GLC were used to monitor the reaction and the isotope effects were determined in order to elucidate the role of the catalyst and the mechanism of hydrogen transfer. In the reaction mixture RuCl2(PPh3)3 is converted by the alcohols into RuH2(CO) (PPh3)3, which then hydrogenates benzylideneacetone. The kinetic data are compatible with the expression. reaction rate = kobs[Ru][olefin][alcohol] The rate-determining step of this reaction is considered to be the transfer of hydrogen from the alcohol to a ruthenium species.

Preparation of 2-substituted benzoxazoles from phenolic Schiff bases by copper(I) chloride-catalyzed oxidation with dioxygen in pyridine

Abstract N-alkylidene-2-hydroxyanilines are oxidized by dioxygen to 2-substituted benzoxazoles in good yields when initiated by copper(I) chloride in pyridine. The overall rate of dioxygen consumption obeys second-order kinetics. The reaction rate is independent of the substrate concentration, indicating that the oxidation of Cu(I) is rate-limiting.

Radical-initiated oxygenation of flavonols by dioxygen

Abstract In the presence of free radicals, such as 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) and 2,6-di-tert-butyl-a-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxyl (galvinoxyl), flavonols undergo catalytic oxygenation to the corresponding depsides (phenolic carboxylic acid esters), with concomitant evolution of CO. The oxygenolysis was performed in aprotic solvents (DMF, MeCN) and was followed by Glc. The results of oxygenation of 4′-substituted flavonols show that the formation of flavonoxy species is the key step in the activation process of the substrate, and that electron-releasing substituents enhance the reaction rate.

Chelated flavonol co-ordination in flavonolatobis(triphenylphosphine)copper(I)

3-Hydroxyflavone co-ordinates to copper(I) by its 3-hydroxy and 4-carbonyl groups together with two triphenylphosphines to form a distorted tetrahedron with a high electron delocalization on the flavonolate ligand, as shown by an X-ray crystal structure determination.

Isoindoline-derived ligands and applications

During the past decade isoindoline-based ligands became the subject of growing interest due to their modular set-up. In this review the structure and reactivity of these ligands and their transition metal complexes are covered. Beyond the discussion of the structural properties particular attention is paid to the expanding fields of applications of these compounds.

Copper-mediated oxygenation of flavonolate in the presence of a tridentate N-ligand. Synthesis and crystal structures of [Cu(fla)(idpaH)]ClO4 and [Cu(idpaH)(O-bs)]ClO4, [fla = flavonolate, idpaH = 3,3'-iminobis(N,N-dimethylpropylamine), O-bs = O-benzoylsalicylate]

Abstract The complexes [Cu(fla)(idpaH)]ClO4 (4) and [Cu(idpaH)(O-bs)]ClO4 (5) (fla=flavonolate, idpaH=3,3′-iminobis(N,N-dimethylpropylamine), O-bs=O-benzoylsalicylate) have been synthesised and characterised. Complex 5 can be obtained also by the oxygenation of 4 and concomitant CO release. The structures of the compounds have been determined by X-ray diffraction. Complex 4 exhibits distorted trigonal-bipyramidal geometry around the copper(II) ion while complex 5 is distorted square-pyramidal.