Outer-sphere electron transfer between (cyclam)nickel(2+) and copper(III) imine-oxime complexes

Hussein, Ali Y T; Sulfab, Yousif; Nasreldin, Mohamed

doi:10.1021/ic00300a035

Cited by 11 publications

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“…In particular, noting that the two complexes appear to have similar square planar geometries with structures that differ only with respect to the metal–ligand bond distances (average Cu–N/O bond shortens by 0.09 Å upon oxidation), we wondered if electron transfer (ET) self-exchange rates would be fast and the associated reorganization energy (λ) would be low. Kinetic studies of ET reactions involving Cu III,II couples are rare, the only examples of which we are aware being those of oligopeptide and imine–oxime complexes . Self-exchange rate constants k 11 ∼ 5 × 10 4 M –1 s –1 and ∼5 × 10 5 M –1 s –1 at 25 °C, respectively, were measured for these complexes in H 2 O. , Reaction entropies for the reduction of Cu III to Cu II were also determined for some oligopeptide complexes, using temperature-dependent cyclic voltammetry in H 2 O and CH 3 CN.…”

Section: Introductionmentioning

confidence: 99%

Low Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple

et al. 2019

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The rate constant for electron self-exchange (k 11 ) between LCuOH and [LCuOH] − (L = bis-2,6-(2,6-diisopropylphenyl)carboximidopyridine) was determined using the Marcus cross relation. This work involved measurement of the rate of the cross-reaction between [Bu 4 N][LCuOH] and [Fc][BAr 4F ] (Fc + = ferrocenium; BAr 4 F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate)) by stopped-flow methods at −88 °C in CH 2 Cl 2 and measurement of the equilibrium constant for the redox process by UV−vis titrations under the same conditions. A value of k 11 = 3 × 10 4 M −1 s −1 (−88 °C) led to estimation of a value 9 × 10 6 M −1 s −1 at 25 °C, which is among the highest values known for copper redox couples. Further Marcus analysis enabled determination of a low reorganization energy, λ = 0.95 ± 0.17 eV, attributed to minimal structural variation between the redox partners. In addition, the reaction entropy (ΔS°) associated with the LCuOH/[LCuOH] − self-exchange was determined from the temperature dependence of the redox potentials, and found to be dependent upon ionic strength. Comparisons to other Cu redox systems and potential new applications for the formally Cu III,II system are discussed.

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Section: Introductionmentioning

confidence: 99%

Low Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple

et al. 2019

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“…The results in Table 3 show that k obs for both H 2 Q and MH 2 Q are independent of pH over the entire pH range studied. The reaction scheme for the reduction of [Cu III B] + may be described by Equations (10), (24) and (25).…”

Section: àD[cumentioning

confidence: 99%

“…The self-exchange rate constant k 11 for Cu III/II couple for the complex [Cu III A] + has been estimated as 5 · 10 5 M )1 s )1 [24]. The self-exchange rate constant for the complex [Cu III B] + has not previously been estimated and the value 5 · 10 5 M )1 s )1 is used.…”

Section: àD[cumentioning

confidence: 99%

“…The exchange rate constant k 22 $ 2 · 10 6 M )1 s )1 seems to work well with derivatives of 1,4-dihydroxybenzene with electron withdrawing substituents, as well as for 1,2-dihydroxybenzene and its derivatives [2a, 23]. The self-exchange rate constant for Cu III/II couples with type H 2 A ligands has been estimated as $5 · 10 5 M )1 s )1 [24]. However, the self-exchange rate constant for copper(III/II) complexes with type H 2 B ligands has not been estimated.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and mechanism of reduction of 2,8-dimethyl-1,9-diphenyl-3,7-diaza-2,7-nonadiene-1,9-dione dioximatocopper(III) ([CuIII A]+) and 4,6,9-trimethyl-5,8-diaza-4,8-dodecadiene-2,3,10,11-tetraone 3,10-dioximatocopper(III) ([CuIIIB]+) by p-methoxyphenol, 1,2-dihydroxybenzene, 1,4-dihydroxybenzene and some of its derivatives

Al-Sogair

Sulfab

2005

Transition Met Chem

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Kinetics and mechanism of reduction of 2,8-dimethyl-1,9-diphenyl-3,7-diaza-2,7-nonadiene-1,9-dione dioximatocopper(III) ([Cu III A] + ) and 4,6,9-trimethyl-5,8-diaza-4,8-dodecadiene-2,3,10,11-tetraone 3,10-dioximatocopper(III) ([Cu III B] + ) by p-methoxyphenol, 1,2-dihydroxybenzene, 1,4-dihydroxybenzene and some of its derivatives q AbstractThe kinetics of reduction of two copper(III)-imine-oxime complexes, [Cu III A] + and [Cu III B] + , (H 2 A and H 2 B ¼ 2, 8-dimethyl-1,9-diphenyl-3,7-nonadiene-1,9-dione dioxime and 4,6,9-trimethyl-5,8-diaza-4,8-dodecadiene-2,3,10,11-tetraone 3,10-dioxime respectively) by hydroquinone (H 2 Q), 2-methylhydroquinone (MH 2 Q), 2-chlorohydroquinone (ClH 2 Q), catechol (H 2 Cat) and p-methoxyphenol (pMHP) have been examined in aqueous acidic solution. Under fixed reaction conditions, the kinetics display first-order dependence on each oxidant and reductant. The pH-dependence is complex for the reduction of [Cu III A] + , since both the copper(III) complex and the reductants undergo protonation-deprotonation equilibria. In the lower pH range, the second-order rate constant, k 2 , decreases with increasing pH. In the higher pH range, k 2 increases with increasing pH. In the lower pH range the most important oxidant is [Cu III HA] 2+ , whereas, in the higher pH range the most important reactants are deprotonated reductants. However for H 2 Cat, as was observed before, two reaction pathways seem to operate in the high pH range. In one pathway, HCat ) seems to be involved; whereas, in the other pathway Cat 2) seems to be the reactive species. Doubly deprotonated catechol, Cat 2) , is very unlikely to be formed at pH £ 5. It was therefore necessary to invoke a strong interaction between [Cu III A] + and HCat ) followed by loss of the second proton. The pH dependence for the reduction of [Cu III B] + is less complex. Thus H 2 Q and MH 2 Q showed no pH dependence up to pH $ 4.60, whereas ClH 2 Q, pMHP and H 2 Cat displayed an inverse first-order dependence on [H + ]. Observed rate constants showing first-order dependence and inverse first-order dependence on [H + ] correlate reasonably well with those calculated using the Marcus equation. The reaction path involving Cat 2) is believed to proceed by an inner-sphere mechanism. The agreement between the calculated and observed values for the [Cu III A] + complex is lower than was found for the [Cu III A 1 ] + (A 1 ¼ 3, 9-diethyl-4,8-diaza-3,8-undeca-2,10-dionedioxime). It seems that the replacement of methyl groups in the latter complex by phenyl groups in the former complex causes both electronic and steric effects, and both effects seem to retard electron transfer. The electronic effect is readily seen in the decrease of the reduction potential of [Cu III A] + (E 0 ¼ 1.09 V) compared to the reduction potential of [Cu III A 1 ] + (E 0 ¼ 1.16 V) and thus making the former a weaker oxidant. The self-exchange rate constant (5 · 10 5 M )1 s )1 ) estimated for complexes with type H 2 A ligands seem to work well for complexes with type H 2 B liga...

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“…Chakravorty and co-workers M -donation have synthesized and characterized the iron(II)/(III) complexes with ligands, H 2 L (3, 14-dimethyl-4,7,10,13tetraazahexadeca-3,13-diene-2,15-dione dioxime) [9 -11] (I). Though the iron(II)/(III) complex of H 2 L has moderate redox potential values and is reasonably stable in aqueous solution [11,12], the kinetic studies on the electron transfer reactions of iron(II)/(III) complexes are scarce [12]. The octahedral iron(II) oxime complexes are reported to be substitutionally inert with lability in the order ca.…”

Section: Introductionmentioning

confidence: 99%

Kinetic studies on the periodate oxidation of an iron(II) oxime-imine complex

Saha

Gangopadhyay

Banerjee

et al. 1999

Int. J. Chem. Kinet.

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The iron(II) complex of H 2 L 14-dimethyl-4, 7, 10, 13-tetraazahexadeca-(H L ϭ 3, 2 3,13-diene-2,15-dione dioxime, Coord. Chem. Rev., 33, 87 (1980)) is oxidized by periodate very rapidly in the range pH 2.0-7.0, and the kinetics of the reaction has been followed by stoppedflow spectrophotometry at 30ЊC and ionic strength (NaClO 4 ). The reaction is Ϫ1 I ϭ 0.20 mol L found to follow a simple second-order kinetics asϩ and IO 3 Ϫ as the final products. The reaction has been proposed to occur through a H-bonded transition state formed probably between the protonated oxime group of the ligand and the oxygen atom on the periodate species, followed by an electron transfer from Fe II centre to I VII in a rate-determining step. The I VI species thus generated reacts in a fast step with another Fe II complex.

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Outer-sphere electron transfer between (cyclam)nickel(2+) and copper(III) imine-oxime complexes

Cited by 11 publications

References 0 publications

Low Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple

Low Reorganization Energy for Electron Self-Exchange by a Formally Copper(III,II) Redox Couple

Kinetic studies on the periodate oxidation of an iron(II) oxime-imine complex

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