Conformationally-controlled electron-transfer reactions as manifested with copper(II)/(I) macrocyclic ligand complexes

Rorabacher, D. B.; Meagher, Nancy E.; Juntunen, Kerri L.; Robandt, Paul V.; Leggett, G. H.; Salhi, Cynthia A.; Dunn, Brian C.; Schroeder, Ronald R.; Ochrymowycz, L. A.

doi:10.1351/pac199365030573

Cited by 24 publications

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“…Application of Square Scheme. Rorabacher et al tried to explain the “gated” electron transfer for copper-cyclic thioether ions using the mechanisms described in Scheme . − They found that the reactions proceed mostly through path A for the copper-thioether complexes by comparing the electron exchange rate constants estimated from both the reduction and oxidation cross reactions.…”

Section: Discussionmentioning

confidence: 99%

“…3 The electron-transfer regulated by the slowness of the change in coordination geometry has been reported for some copper(II/ I) couples with tetrathiamacrocyclic ligands. [4][5][6][7][8] Rorabacher et al precisely explored such "gated behavior" caused by sluggishness in the geometric interconversion and discovered that the oxidation of tetrahedral Cu(I) to tetragonal Cu(II) is slow in most cases when macrocyclic thioether ligands were used. In such cases, the electron exchange rate constant estimated by the application of the Marcus cross relation to the oxidation reaction of Cu(I) was not consistent with the directly measured electron exchange rate constant by using NMR.…”

Section: Introductionmentioning

confidence: 99%

“…The electron-transfer regulated by the slowness of the change in coordination geometry has been reported for some copper(II/I) couples with tetrathiamacrocyclic ligands. − Rorabacher et al. precisely explored such “gated behavior” caused by sluggishness in the geometric interconversion and discovered that the oxidation of tetrahedral Cu(I) to tetragonal Cu(II) is slow in most cases when macrocyclic thioether ligands were used.…”

Section: Introductionmentioning

confidence: 99%

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An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

et al. 1999

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Reduction reactions of Cu(dmp)(2)(2+) (dmp = 2,9-dimethyl-1,10-phenanthroline) by ferrocene (Fe(Cp)(2) = bis(cyclopentadienyl)iron(II)), decamethylferrocene (Fe(PMCp)(2) = bis(pentamethylcyclopentadienyl)iron(II)), and Co(bpy)(3)(2+) (bpy = 2,2'-bipyridine) and oxidation reactions of Cu(dmp)(2)(+) by Ni(tacn)(2)(3+) (tacn = 1,4,7-triazacyclononane) and Mn(bpyO(2))(3)(3+) (bpyO(2) = N,N'-dioxo-2,2'-bipyridine) were studied in acetonitrile for the purpose of interpreting the gated behavior involving copper(II) and -(I) species. It was shown that the electron self-exchange rate constants estimated for the Cu(dmp)(2)(2+/+) couple from the oxidation reaction of Cu(dmp)(2)(+) by Ni(tacn)(2)(3+) (5.9 x 10(2) kg mol(-)(1) s(-)(1)) and Mn(bpyO(2))(3)(3+) (2.9 x 10(4) kg mol(-)(1) s(-)(1)) were consistent with the directly measured value by NMR (5 x 10(3) kg mol(-)(1) s(-)(1)). In contrast, we obtained the electron self-exchange rate constant of Cu(dmp)(2)(2+/+) as 1.6 kg mol(-)(1) s(-)(1) from the reduction of Cu(dmp)(2)(2+) by Co(bpy)(3)(2+). The pseudo-first-order rate constant for the reduction reaction of Cu(dmp)(2)(2+) by Fe(Cp)(2) was not linear against the concentration of excess amounts of Fe(Cp)(2). A detailed analysis of the reaction revealed that the reduction of Cu(dmp)(2)(2+) involved the slow path related to the deformation of Cu(dmp)(2)(2+) (path B in Scheme 1). By using Fe(PMCp)(2) (the E degrees value is 500 mV more negative than that of Fe(Cp)(2)(+/0)) as the reductant, the mixing with another pathway involving deformation of Cu(dmp)(2)(+) (path A in Scheme 1) became more evident. The origin of the "Gated Behavior" is discussed by means of the energy differences between the "normal" and deformed Cu(II) and Cu(I) species: the difference in the crystal field activation energies corresponding to the formation of pseudo-tetrahedral Cu(II) from tetragonally distorted Cu(II) and the difference in the stabilization energies of the tetrahedral and tetragonal Cu(I) for the activation of Cu(I) species. The reduction reaction of Cu(dmp)(2)(2+) by Fe(PMCp)(2) confirmed that the mixing of the two pathways takes place by lowering the energy level corresponding to the less favorable conformational change of Cu(I) species.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

et al. 1999

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“…The reaction of [Cu(dmbp) 2 ] 2+ and [Cu(dmp) 2 ] + in acetonitrile was first-order for up to five half-lives and was described by eqn. (10) under the pseudo-first-order conditions of [Cu(dmbp…”

Section: Pseudo-electron Self-exchange Reaction Between [Cu(dmp) 2 ] ...mentioning

confidence: 99%

“…Among investigations carried out to date, intensive and systematic studies by Rorabacher and co-workers seem to have largely improved understandings of the gated phenomena: they examined ET reactions of Cu(II)/(I)-macrocyclic polythioether complexes and found that the coordination structural change takes place essentially at the Cu(I) site while the coordination geometry around the Cu(II) species is not largely altered. [8][9][10][11][12] They related this phenomenon to the biologically important catalytic processes and postulated a dual-pathway Square Scheme described in Scheme 1. Rorabacher recently reviewed ET reactions by Cu(II)/(I) centers, 13 in which he seems to have confirmed that the gated ET reactions exhibited by copper complexes are successfully explained by this scheme.…”

Section: Introductionmentioning

confidence: 99%

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane

et al. 2005

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[Cu(2,9-dimethyl-1,10-phenanthroline)(2)](2+) and [Cu(6,6'-dimethyl-2,2'-bipyridine)(2)](2+/+) complexes with no coordinated solvent molecule were synthesized and the crystal structures were analyzed: the coordination geometry around the Cu(i) center was in the D(2d) symmetry while a D(2) structure was observed for the four-coordinate Cu(ii) complexes. Coordination of a water or an acetonitrile molecule was found in the trigonal plane of the five-coordinate Cu(ii) complex in the Tbp(trigonal bipyramidal) structure. Spectrophotometric analyses revealed that the D(2) structure of the Cu(ii) complex was retained in nitromethane, although a five-coordinate Tbp species (green in color), was readily formed upon dissolution of the solid (reddish brown) in acetonitrile. The electron self-exchange reaction between D(2d)-Cu(I) and D(2)-Cu(II), observed by the NMR method, was very rapid with k(ex)=(1.1 +/- 0.2) x 10(5) kg mol(-1) s(-1) at 25 degrees C (DeltaH*= 15.6 +/- 1.3 kJ mol(-1) and DeltaS*=-96 +/- 4 J mol(-1) K(-1)), which was more than 10 times larger than that reported for the self-exchange reaction between D(2d)-Cu(I) and Tbp-Cu(II) in acetonitrile. The cross reduction reactions of D(2)-Cu(ii) by ferrocene and decamethylferrocene in nitromethane exhibited a completely gated behavior, while the oxidation reaction of D(2d)-Cu(i) by [Ni(1,4,7-triazacyclononane)(2)](3+) in nitromethane estimated an identically large self-exchange rate constant to that directly obtained by the NMR method. The electron self-exchange rate constant estimated from the oxidation cross reaction in 50% v/v acetonitrile-nitromethane mixture was 10 times smaller than that observed in pure nitromethane. On the basis of the Principle of the Least Motion (PLM) and the Symmetry Rules, it was concluded that gated behaviors observed for the reduction reactions of the five-coordinate Cu(ii)-polypyridine complexes are related to the high-energy C(2v)--> D(2d) conformational change around Cu(ii), and that the electron self-exchange reactions of the Cu(ii)/(i) couples are always adiabatic through the C(2v) structures for both Cu(ii) and Cu(i) since the conformational changes between D(2d), D(2) and C(2v) structures for Cu(i) as well as the conformational change between Tbp and C(2v) structures for Cu(ii) are symmetry-allowed. The completely gated behavior observed for the reduction reactions of D(2)-Cu(ii) species in nitromethane was attributed to the very slow conformational change from the ground-state D(2) to the entatic D(2d) structure that is symmetry-forbidden for d(9) metal complexes: the very slow back reaction, the forbidden conformational change from entatic D(2d) to the ground-state D(2) structure, ensures that the rate of the reduction reaction is independent of the concentration of the reducing reagent.

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Host‐Guest and Cage‐Type Systems

Fabbrizzi¹,

Licchelli²,

Taglietti³

2001

Electron Transfer in Chemistry

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Conformationally-controlled electron-transfer reactions as manifested with copper(II)/(I) macrocyclic ligand complexes

Abstract: Abstract

Cited by 24 publications

References 0 publications

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane

Host‐Guest and Cage‐Type Systems

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Conformationally-controlled electron-transfer reactions as manifested with copper(II)/(I) macrocyclic ligand complexes

Abstract: Abstract

Cited by 24 publications

References 0 publications

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

An Interpretation of Gated Behavior: Kinetic Studies of the Oxidation and Reduction Reactions of Bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in Acetonitrile

Syntheses, structural analyses and redox kinetics of four-coordinate [CuL2]2+and five-coordinate [CuL2(solvent)]2+complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)2]2+in nitromethane

Host‐Guest and Cage‐Type Systems

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Syntheses, structural analyses and redox kinetics of four-coordinate [CuL₂]²⁺and five-coordinate [CuL₂(solvent)]²⁺complexes (L = 6,6′-dimethyl-2,2′-bipyridine or 2,9-dimethyl-1,10-phenanthroline): completely gated reduction reaction of [Cu(dmp)₂]²⁺in nitromethane