| Abstract
| - Both the reduction and oxidation kinetics of CuII/I([18]aneS6) have been studied in acetonitrile solution using a series of counter reagents to determine the electron self-exchange rate constant (k11) for this complex. The resolved value of k11 = 3 × 103 M-1 s-1 is significantly smaller than values for related complexes involving homoleptic thioether ligands with all ethylene bridges. This is attributed to the fact that two Cu−S bonds must be ruptured upon reduction with a concomitant larger rearrangement in the coordinate bond angles.
- The electron-transfer kinetics of the complex formed by copper(II/I) with the sexadentate macrocyclic ligand1,4,7,10,13,16-hexathiacyclooctadecane ([18]aneS6) have been measured in acetonitrile with a series of three oxidizingagents and three reducing agents. These studies have been supplemented by determinations of the redox potentialand the stability constants of the CuI- and CuII([18]aneS6) complexes in both acetonitrile and aqueous solution. TheMarcus cross relationship has been applied to the cross-reaction rate constants for the six reactions studied toresolve the electron self-exchange rate constant for the CuII/I([18]aneS6) complex. An average value of k11 = 3 ×103 M-1 s-1 was obtained at 25 °C, μ = 0.10 M in acetonitrile. This value is approximately 2 orders of magnitudesmaller than the values reported previously for the corresponding Cu(II/I) complexes with the quadridentate andquinquedentate homoleptic homologues having all ethylene bridges, namely, 1,4,7,10-tetrathiacyclododecane([12]aneS4) and 1,4,7,10,13-pentathiacyclopentadecane ([15]aneS5). This significant difference in reactivity is attributedto the greater rearrangement in the geometry of the inner-coordination sphere that accompanies electron transferin the CuII/I([18]aneS6) system, wherein two Cu−S bonds are ruptured upon reduction. In contrast to other Cu(II/I)complexes with macrocyclic polythiaethers that have self-exchange rate constants within the same range, no evidencefor conformationally gated electron transfer was observed, even in the case of the most rapid oxidation reactionstudied.
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