Stoichiometry and kinetics of low-temperature oxidation of di-.mu.-chlorobis(N,N,N',N'-tetraethylethylenediamine)dicopper by dioxygen in methylene chloride and properties of the peroxocopper products

et al. 2005

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This paper describes the synthesis and characterization of heteropolynuclear redox active materials [FerCuCl] 4 YY¢, Y = Y¢ = O, Y = Y¢ = Cat and Y = O, Y¢ = Cat, Fer = N,N-dimethylaminomethylferrocene and Cat = 3,4, 5,6-tetrachlorocatecholato ligand. Manometric O 2 uptake measurements in PhNO 2 show that tetranuclear [FerCuCl] 4 and [FerCuCl] 4 Cat give the tetranuclear oxocopper(II) products [FerCuCl] 4 O 2 and [FerCuCl] 4 CatO, respectively. The absence of carbonyl stretching vibrational bands in [FerCuCl] 4 Cat 2 and [FerCuCl] 4 CatO suggest that tetrachloro-1,2-benzoquinone (TClBQ) is reduced to the corresponding catecholete during the oxidation of copper(I) centers in [FerCuCl] 4 . The near i.r. electronic spectra for [FerCuCl] 4 O 2 , [FerCuCl] 4 CatO and [FerCuCl] 4 Cat 2 exhibit broad intense split maxima in the 750-875 nm range, attributed to a minimum of three halide ligands per Cu. Room temperature solid state e.p.r. spectra for [FerCuCl] 4 CatO and [FerCuCl] 4 Cat 2 are of the axial type, suggesting a square pyramidal geometry around Cu II .

Section: Methodsmentioning

confidence: 99%

“…O 2 was then bubbled through each solution for 10 min, to observe the formation Measured in nitrobenzene at (3-5) · 10 )2 molal concentration [16]. of 3,3¢,5,5¢-tetramethyl-4,4¢-diphenoquinone (DPQ) (k max = 431 nm, 2= (5.05±0.01) · 10 4 M )1 cm )1 ) [22].…”

Section: Test Of Catalytic Activitymentioning

confidence: 99%

Synthesis and Characterization of Heteropolynuclear Redox Active Materials[FerCuCl]4YY′; Y = Y′ = O, Y = Y′ = Cat and Y = O, Y′ = Cat, Fer = N,N-dimethylaminomethylferrocene and Cat = 3,4,5,6-tetrachlorocatecholato Ligand

Elsayed

Abdel-Salam

et al. 2005

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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. 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.…”

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

et al. 2005

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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).

“…Particular attention has been focused on the reactions of halo(amine)copper(I) complexes with O 2 which are the basis of many useful catalytic systems [4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Oxidation of bis(µ-halo)-bis[(diamine)copper(I)] complexes [LCuX]2; L = TMED, X = Cl, Br or I, L = TEED or TMPD, X = Cl, with the two electron organo oxidizing agent, tetrachloro-1,2-benzoquinone(TClBQ) in aprotic media: models for intermediates in catalytic catechol oxidase

El-Sayed

Abdel-Hamid

et al. 2006

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Well structurally characterized bis(l-halo)-bis[(diamine)copper(I)] complexes [LCuX] 2 ; L = TMED, tetramethylethylenediamine, X = Cl, Br or I and L = TEED, tetraethylethylenediamine, or TMPD, tetramethylpropanediamine, X = Cl, react quantitatively with tetrachloro-1,2-benzoquinone (TClBQ) as two electron oxidizing agent in O 2 -free CH 2 Cl 2 or PhNO 2 to form a dimeric [LCuX] 2 Cat (Cat = catechol) as indicated by cryoscopic measurements. Infrared spectra was in agreement with total reduction of TClBQ to the corresponding catechol. Electronic spectra indicated a dimeric distorted five coordinate Cu(II) and EPR spectra suggested a square pyramidal arrangement around the Cu(II) centers in [LCuX] 2 Cat. The ligand field strength for diamine ligand was higher for the five member chelating ring (TMED) relative to the six membered one (TMPD). Electrochemical reduction of Cu centers in [LCuX] 2 Cat were irreversible and occurred at a less negative potential when X = I.