Homogeneous oxidative coupling catalysts. Mechanism of catalysts formation by oxidation of [(Pip)nCuX]4 (n=1 or 2, Pip=piperidine, X=Cl, Br or I) by dioxygen in aprotic media

El-Sayed, Mohamed A.; Kassem, Taher S.; Abo-El-Dahab, Hisham A.; Elkholy, A.

doi:10.1016/j.ica.2004.08.025

Cited by 11 publications

(7 citation statements)

References 10 publications

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“…This usually happens when Cl is changed to Br or I in similar core structures. [42][43][44] The cyclic voltammetry of 2 shows two anodic peaks potential at 0.716 and 0.898 V and two cathodic peaks at 0.731 and 0.530 V. We could not get any wave for the oxidation of copper(II) to copper(III) in the potential range up to 1.6 V.…”

Section: Supplementary Materialsmentioning

confidence: 89%

Synthesis, Structure and Electrochemistry of Tetranuclear Oxygen-Centered Copper(II) Clusters with Acetylacetone and Benz-pyrazole Hydrolyzed Derivatives as Ligand

Vafazadeh

Willis²

2016

ACSi

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Two copper(II) clusters Cu 4 OCl 6 (pyrazole) 4 (1) and Cu 4 OBr 6 (Br-pyrazole) 4 (2) have been synthesized by reacting acetylacetone and benzohydrazide (1:1 ratio) with CuX 2 (X = Cl for 1 and X = Br for 2) in methanol solution. The structures of both clusters have been established by X-ray crystallography. The clusters contain four Cu, one O, six μ 2 -X atoms, and four pyrazole ligands. The pyrazole was prepared in situ by the reaction of acetylacetone with benzohydrazide in methanol under reflux. In 2, the methine hydrogen of the pyrazole ligand has been replaced by bromine atom. The four copper atoms encapsulate the central O atom in a tetrahedral arrangement. All copper atoms are five-coordinate and have similar coordination environments with slightly distorted trigonal bipyramidal geometry. The cyclic voltammogram of the clusters 1 and 2 show a one-electron quasi-reversible reduction wave in the region 0.485 to 0.731 V, and a one-electron quasi-reversible oxidation wave in the region 0.767 to 0.898 V. In 1, one irreversible oxidative response is observed on the positive of side of the voltammogram at 1.512 V and this can be assigned to Cu(II) to Cu(III) oxidation.

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Section: Supplementary Materialsmentioning

confidence: 89%

Synthesis, Structure and Electrochemistry of Tetranuclear Oxygen-Centered Copper(II) Clusters with Acetylacetone and Benz-pyrazole Hydrolyzed Derivatives as Ligand

Vafazadeh

Willis²

2016

ACSi

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“…Oxidation of copper(I) complexes by dioxygen operated by k on ¼ Kk 2 [3][4][5][6]. For oxidation of halo-amine copper(I) complexes, the pre-equilibrium, K, between copper(I) center and dioxygen was negligible in all studied cases [7][8][9], except for [(TEED)CuCl] 2 [3] at low temperature.…”

Section: Introductionmentioning

confidence: 95%

“…The existence of hydrogen bond association with the incoming dioxygen as in the case of [(DEED)CuBr] 2 [4] let K operate up to 30°C. High basicity of piperidine and its piperidyl hydrogen were behind (a) oxidation of [CuI] 4 core by increasing K, which was impossible in case of pyridine type ligands [10]; (b) increasing the rate of oxidation k on and (c) changing the reaction from endothermic as in pyridine type of ligands [7][8][9] to exothermic one due to promotion of pre-equilibrium K [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Oxidation of tetranuclear copper(I) complexes [(Pip)nCuX]4; n=1 or 2, Pip=Piperidine and X=Cl or Br, with two equivalents of tetrachloro-1,2-benzoquinone (TClBQ) and sequentional oxidation with one equivalent of TClBQ followed by dioxygen in aprotic media: Models for intermediates in catalytic catechol–copper(II) systems

El-Sayed

Abdel-Salam

El-Zayat

et al. 2005

Transition Met Chem

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Copper(I) halides react quantitatively with piperidine in dioxygen-free CH 2 Cl 2 or PhNO 2 to form tetranuclear copper(I) complexes [(pip) n CuX] 4 ; n ¼ 1 or 2 and X ¼ Cl or Br. These complexes are very soluble in CH 2 Cl 2 and PhNO 2 and completely reduce tetrachloro1,2-benzoquinone (TClBQ) and O 2 to the 3,4,5,6-tetrachlorocatecholato ligand (Cat) and the oxo form. The stable solid complexes [(pip) n CuX] 4 Cat 2 and [(pip) n CuX] 4 CatO are closely related to the intermediate, bridging l-catecholato complex, which is formed during the mono-oxygenation and oxidation of PhOH by oxytyrosinase. Cryoscopic and analytical data for these complexes indicate that [(pip) n CuX] 4 Cat 2 and [(pip) n CuX] 4 CatO are discrete tetranuclear species. Electronic transition spectra in the near i.r. with high molecular absorptivity are diagnostic for a tetranuclear 'Cu 4 X 4 ' core structure. The electronic transitions are more likely to be due to charge transfer between a minimum of three halo ligands to the copper(II) center. The room temperature e.p.r. spectra of [(pip) n CuX] 4 Cat 2 and [(pip) n CuX] 4 CatO in CH 2 Cl 2 are isotropic with four hyperfine lines. The room temperature solid state e.p.r. spectra of these complexes show an axial spectra with d x 2) y 2 ground state, suggesting a square pyramidal arrangement around copper(II) centers in all n ¼ 1 complexes and an elongated tetragonal octahedral arrangement around copper(II) centers in all n ¼ 2 complexes. Cyclic voltammetry measurements show that they are more likely to be irreversible and show slight quasi-reversibility when X ¼ Br and n ¼ 2. Constant potential electrolysis indicate that the number of electrons consumed are equal to four which will be due to the reduction of four copper(II) species to copper(I).

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“…Among other significant applications, piperidine derivatives are used as analgesics [1] and anti-bactericides [2] or used to treat schizophrenia, Parkinson and Alzheimer diseases [3][4][5]. Metal complexes with ligands containing the six-membered saturated heterocyclic ring were also found to have important catalytic or pharmacological applications [6][7][8] and, therefore, it is not surprising that strong efforts are being devoted to the synthesis of new organometallic compounds containing at least a piperidine ring [9,10].…”

Section: Introductionmentioning

confidence: 99%