Electron-transfer reactions of copper(II) complexes containing trioether sulfur and pyridyl nitrogen donors with ferrocene and 1,1′-dimethylferrocene

[CuII(bib)2]2+ and [CuI(bib)2]+ (bib = 2,2‘-bis(2-imidazolyl)biphenyl) have similar geometries, with the Cu(II) complex best described as pseudo-square planar and the Cu(I) complex pseudo-tetrahedral. The cyclic voltammograms in acetonitrile are only quasi-reversible, with ΔE p/p ∼ 103 mV, which leads to uncertainty in E 1/2. UV−vis measurements of the reaction [CuII(bib)2]2+ + [CoII((nox)3(BC6H5)2)] ⇌ [CuI(bib)2]+ + [CoIII((nox)3(BC6H5)2)]+ ((nox)3(BC6H5)2 = a clathrochelate ligand) yield K = 2.6 in acetonitrile at 25 °C with μ = 0.1 M (Et4NBF4). Using the known E° for the CoIII/II couple yields E° = 0.274 V vs Ag/AgCl for [CuII/I(bib)2]2+/+. This, in turn, leads to K = 72 for reaction with [CoII((nox)3(BC4H9)2)]. The reaction of [CuII(bib)2]2+ with [CoII((nox)3(BC4H9)2)] obeys simple bimolecular kinetics with k = 87 M-1 s-1. Similar behavior occurs with [CoII((nox)3(BC6H5)2)] and [CoII((dmg)3(BC4H9)2)] as reductants. A value of k 11 = 0.16 M-1 s-1 is calculated for the [CuII(bib)2]2+/[CuI(bib)2]+ self-exchange reaction based on the Marcus cross-exchange relationship and the known electron-self-exchange rate constants for the Co(III)/Co(II) couples. This value of k 11 is remarkably small for a Cu(II/I) system, especially in view of the small structural change at copper (Δ(Cu−N)ave = 0.07 Å) during redox turnover. However, molecular mechanics calculations with newly developed copper force fields demonstrate ΔG ‡ in to be the major factor that accounts for the small value of k 11. Much of this large reorganization energy appears to arise from angular distortions around copper. Nevertheless, the structural changes for the [CuII/I(bib)2]2+/+ couple are small relative to those for systems that have much greater self-exchange rate constants. These considerations underscore the difficulties in applying the entatic hypothesis to cuproprotein active sites.

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“…d First-order rate constant in units of s -1 . e Reactions in acetonitrile with ferrocenes show rate saturation indicative of prior association …”

Section: Discussionmentioning

confidence: 99%

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [Cu^II/I(bib)₂]^2+/+ Couple

et al. 1998

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“…Tanaka and co-workers have also studied several related bis-complexes in which each bidentate ligand contained one unsaturated nitrogen and a thiaether sulfur. 148,150 In most of the foregoing studies, Tanaka and coworkers observed that, in reduction of the Cu II L or Cu II L 2 complexes with excess ferrocene (or 1,2-dimethylferrocene) in either methanol or acetone, the observed pseudo-first-order rate constant curved off with increasing ferrocene concentration. In their original paper, 150 Tanaka and co-workers interpreted this behavior in terms of a mechanism in which the Cu II L complex formed a strong equilibrated outersphere complex with the ferrocene reagent (characterized by the equilibrium constant, K) followed by electron-transfer as the rate-determining step, k et :…”

Section: Thiaether Sulfur−imine Nitrogen Mixed Donor Ligand Systemsmentioning

confidence: 98%

“…Additional reduction studies have been reported by Karlin and Yandell 147 and by Tanaka and co-workers. 148 The calculated k 11(Red) within the range of 0.1-10 M -1 s -1 . The only known Cu I L oxidation kinetic study involved a back reaction with Ru III (NH 3 ) 4 bpy 3+ .…”

Section: Thiaether Sulfur−imine Nitrogen Mixed Donor Ligand Systemsmentioning

confidence: 99%

“…In addition to their studies on the pdto system, Tanaka and co-workers 148 have reported electrontransfer kinetic studies in methanol on a closely related ligand in which the sulfur-pyridine linkages were decreased by one carbon (pmto, Figure 11), and a third correlated study involved the expansion of the bridge between the two sulfur donor atoms (pmpo, Figure 11). These investigators also reported electrontransfer kinetic studies on a similar ligand (bidto, Figure 11) involving terminal imidazole groups in place of the pyridines.…”

Section: Thiaether Sulfur−imine Nitrogen Mixed Donor Ligand Systemsmentioning

confidence: 99%

“…In a subsequent paper, 148 Tanaka and co-workers recognized the possibility of an alternate mechanism in which the limiting first-order process was due to the desolvation of the Cu II L complex. This latter mechanism is equivalent to pathway B in Scheme 1.…”

Section: Thiaether Sulfur−imine Nitrogen Mixed Donor Ligand Systemsmentioning

confidence: 99%

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Electron Transfer by Copper Centers

2004

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Redox Reactions between Two Metal Complexes

Twigg¹

1989

Mechanisms of Inorganic and Organometallic Reactions

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The investigations of the kinetics and mechanisms of electron transfer between metal complexes are continuing to diversify, from the reactions of octahedral species in aqueous solution to systems involving less common metals and coordination geometries in nonaqueous media. The activity in the study of electron transfer reactions involving metalloproteins is increasing rapidly, with an emphasis on the rate dependencies on distance and free energy. The format of the Chapter remains much the same as in previous volumes, with sections covering metal aqua and oxo ions, metal ion complexes, and metalloproteins. The rate and activation parameters are presented in four tables, with the data for electron transfer reactions between metal complexes in Table 2.1, directly measured electron self-exchange rate data in Table 2.2, and the data for intramolecular and bimolecular reactions involving metalloproteins in Tables 2.3 and 2.4, respectively. The discussion in each section of the text and the data in the tables are arranged, for the most part, in the order of increasing atomic number of the central metal ion in the reductant. Reactions of Metal Aqua and Oxo Ions 2.2.1. Titanium{III) and (IV)The variety of kinetic behaviors observed in the reductions of [(NH 3 )sRuX](3-n)+ (X n -= SO~-, S20j-, and NH 2 S0 3 ) by Ti3+ has been interpreted in terms of the ability of sulfato ligands to mediate electron transfer.(1) Outer-sphere reductions occur when x n -= NH2S03 or SO~-, with Ti3+ and 27 M. V. Twigg (ed.), Mechanisms of Inorganic and Organometallic Reactions © Plenum Press, New York 1989 28 2 • Redox Reactions between Two Metal Complexes 2.2.3. Chromium(II} The reduction of the [M020iH20 )6]2+ ion by a large excess of Cr2+ proceeds via an intermediate {Mo(IIIh[ 4Cr(IIII)]} which is formed rapidly (kl = 9.1 X 10 3 M-3 S-I) with the rate law (2) and decays slowly (k2 = 2.0 X lO-s M-I S-I) to Rate = k l [Cr2+]2[Mo(V)2][H+] (2) the Mo(IIIh product.(7) A second intermediate {Mo(IVh[2Cr(III)]} is observed when the reaction is carried out at a Cr: Mo ratio of 2: 1, leading to the production 2.2 • Reactions of Metal Aqua and Oxo Ions 29 of[M0 3 0 4(H20)9]4+. This Mo(IVh trimer is reduced with excess Cr+ in a two-stage process, the first of which is an inner-sphere reaction with an inverse acid dependence. The dimolybdate ions [Moz(j. L-X)(JL-Cl)2CI6]3-(X = H, Cl) undergo a two-electron reduction by Cr+ in acidic chloride solution to yield the [M02Cls]4ion, which catalyzes the anaerobic oxidation of Cr+ to Cr(I1I).(S)The product of the reduction of[ Co(bpy h]3+ by Cr+, upon aerial oxidation, is a red dimeric species, postulated to have the structure [(H20)4Cr(JL-OH)2Cr(OH2)2]4+.(9) This product and the stoichiometry of the reaction suggests a two-electron process, with the bpy ligand serving as a temporary bridging radical. An investigation of the Cr(I1) reduction of [Co(pdh] (pd = pentane-2,4-dione) in water/acetone mixtures reveals outer-sphere, and mono-and di-bridged ([H+r l dependent) pathways. (10) The effect of the cosolvent ...

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Electron-transfer reactions of copper(II) complexes containing trioether sulfur and pyridyl nitrogen donors with ferrocene and 1,1′-dimethylferrocene

Cited by 8 publications

References 6 publications

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [Cu^II/I(bib)₂]^2+/+ Couple

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [Cu^II/I(bib)₂]^2+/+ Couple

Electron Transfer by Copper Centers

Redox Reactions between Two Metal Complexes

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Electron-transfer reactions of copper(II) complexes containing trioether sulfur and pyridyl nitrogen donors with ferrocene and 1,1′-dimethylferrocene

Cited by 8 publications

References 6 publications

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [CuII/I(bib)2]2+/+ Couple

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [CuII/I(bib)2]2+/+ Couple

Electron Transfer by Copper Centers

Redox Reactions between Two Metal Complexes

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Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [Cu^II/I(bib)₂]^2+/+ Couple

Internal Reorganization Energies for Copper Redox Couples: The Slow Electron-Transfer Reactions of the [Cu^II/I(bib)₂]^2+/+ Couple