Effect of Conformational Constraints on Gated Electron-Transfer Kinetics. 3. Copper(II/I) Complexes with cis- and trans-Cyclopentanediyl-1,4,8,11-tetrathiacyclotetradecane
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- 作者：Prabodha Wijetunge ; Chandrika P. Kulatilleke ; Luke T. Dressel ; Mary Jane Heeg ; L. A. Ochrymowycz ; and D. B. Rorabacher
- 刊名：Inorganic Chemistry
- 出版年：2000
- 出版时间：June 26, 2000
- 年：2000
- 卷：39
- 期：13
- 页码：2897 - 2905
- 全文大小：148K
- 年卷期：v.39,no.13(June 26, 2000)
- ISSN：1520-510X
文摘
Previous kinetic and electrochemical studies of copper complexes with macrocyclic tetrathiaethers-such as 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4)-have indicated that electron transfer and the accompanying conformationalchange occur sequentially to give rise to a dual-pathway mechanism. Under appropriate conditions, theconformational change itself may become rate-limiting, a condition known as "gated" electron transfer. We haverecently hypothesized that the controlling conformational change involves inversion of two donor atoms, whichsuggests that "gated" behavior should be affected by appropriate steric constraints. In the current work, twoderivatives of [14]aneS4 have been synthesized in which one of the ethylene bridges has been replaced by eithercis- or trans-1,2-cyclopentane. The resulting copper systems have been characterized in terms of their CuII/ILpotentials, the stabilities of their oxidized and reduced complexes, and their crystal structures. The electron self-exchange rate constants have been determined both by NMR line-broadening and by kinetic measurements oftheir rates of reduction and oxidation with six or seven counter reagents. All studies have been carried out at 25
C, 
= 0.10 M (NaClO4 and/or Cu(ClO4)2), in aqueous solution. Both Cu(II/I) systems show evidence of adual-pathway mechanism, and the electron self-exchange rate constants representative of both mechanistic pathwayshave been determined. The first-order rate constant for gated behavior has also been resolved for the CuI(trans-cyclopentane-[14]aneS4) complex, but only a limiting value can be established for the corresponding cis-cyclopentane system. The rate constants for both systems investigated in this work are compared to values previouslydetermined for the Cu(II/I) systems with the parent [14]aneS4 macrocycle and its derivatives involving phenyleneand cis- or trans-cyclohexane substituents. The results are discussed in terms of the influence of the fused ringson the probable conformational changes accompanying the electron-transfer process.
C, = 0.10 M (NaClO4 and/or Cu(ClO4)2), in aqueous solution. Both Cu(II/I) systems show evidence of adual-pathway mechanism, and the electron self-exchange rate constants representative of both mechanistic pathwayshave been determined. The first-order rate constant for gated behavior has also been resolved for the CuI(trans-cyclopentane-[14]aneS4) complex, but only a limiting value can be established for the corresponding cis-cyclopentane system. The rate constants for both systems investigated in this work are compared to values previouslydetermined for the Cu(II/I) systems with the parent [14]aneS4 macrocycle and its derivatives involving phenyleneand cis- or trans-cyclohexane substituents. The results are discussed in terms of the influence of the fused ringson the probable conformational changes accompanying the electron-transfer process.