Use of Medium Effects to Tune the E1/2 Values of Bimetallic and Oligometallic Compounds
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- 作者：Fré ; dé ; ric Barriè ; re ; Nicole Camire ; William E. Geiger ; Ulrich T. Mueller-Westerhoff ; and Richard Sanders
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：June 26, 2002
- 年：2002
- 卷：124
- 期：25
- 页码：7262 - 7263
- 全文大小：43K
- 年卷期：v.124,no.25(June 26, 2002)
- ISSN：1520-5126
文摘
The redox potentials of bis(fulvalene)dinickel, 1, and the tetrakis(ferrocenyl)nickel dithiolene complex 2 have been measured in a variety of nonaqueous electrolytes. The difference in E1/2 values of the two successive one-electron oxidations of 1 (i.e., 
E1/2 values) increased from a low of 212 mV in anisole/[NBu4]Cl to a high of 850 mV in CH2Cl2-Na[B(C6H3(CF3)2)4], reflecting an increase of over 1010 in the comproportionation constant (Kcomp = [1+]2/[1][12+]). Six reversible one-electron processes are possible for compound 2, the four oxidations arising from the ferrocenyl substituents, and the two reductions arising from the Ni dithiolene moiety. The E1/2 spreads of the four oxidation waves and the two reduction waves are both highly sensitive to medium effects. For both 1 and 2, the largest E1/2 values for cationic products are found in solvents of low polarity and donor strength containing electrolyte salts having large anions and small cations. Conversely, the smallest E1/2 values for anionic products are found under these conditions, culminating in the observation of a single two-electron reduction wave for 2/22- in CH2Cl2-Na[B(C6H3(CF3)2)4]. A combination of solvation and ion-pairing effects must be considered, and may be used to advantage, when using E1/2 values as a measure of electronic interactions between redox centers in compounds containing two or more electron-transfer sites.
E1/2 values) increased from a low of 212 mV in anisole/[NBu4]Cl to a high of 850 mV in CH2Cl2-Na[B(C6H3(CF3)2)4], reflecting an increase of over 1010 in the comproportionation constant (Kcomp = [1+]2/[1][12+]). Six reversible one-electron processes are possible for compound 2, the four oxidations arising from the ferrocenyl substituents, and the two reductions arising from the Ni dithiolene moiety. The E1/2 spreads of the four oxidation waves and the two reduction waves are both highly sensitive to medium effects. For both 1 and 2, the largest E1/2 values for cationic products are found in solvents of low polarity and donor strength containing electrolyte salts having large anions and small cations. Conversely, the smallest E1/2 values for anionic products are found under these conditions, culminating in the observation of a single two-electron reduction wave for 2/22- in CH2Cl2-Na[B(C6H3(CF3)2)4]. A combination of solvation and ion-pairing effects must be considered, and may be used to advantage, when using E1/2 values as a measure of electronic interactions between redox centers in compounds containing two or more electron-transfer sites.