Influence of Electronic and Structural Effects on the Oxidative Behavior of Nickel Porphyrins
详细信息 查看全文
- 作者：Karl M. Kadish ; Min Lin ; Eric Van Caemelbecke ; Guido De Stefano ; Craig J. Medforth ; Daniel J. Nurco ; Nora Y. Nelson ; Bé ; né ; dicte Krattinger ; Cinzia M. Muzzi ; Laurent Jaquinod ; Yang Xu ; Dav
- 刊名：Inorganic Chemistry
- 出版年：2002
- 出版时间：December 16, 2002
- 年：2002
- 卷：41
- 期：25
- 页码：6673 - 6687
- 全文大小：225K
- 年卷期：v.41,no.25(December 16, 2002)
- ISSN：1520-510X
文摘
With the aim of better understanding the electronic and structural factors which govern electron-transfer processesin porphyrins, the electrochemistry of 29 nickel(II) porphyrins has been examined in dichloromethane containingeither 0.1 M tetra-n-butylammonium perchlorate (TBAP) or tetra-n-butylammonium hexafluorophosphate (TBAPF6)as supporting electrolyte. Half-wave potentials for the first oxidation and first reduction are only weakly dependenton the supporting electrolyte, but E1/2 for the second oxidation varies considerably with the type of supportingelectrolyte. E1/2 values for the first reduction to give a porphyrin 
-anion radical are effected in large part by theelectronic properties of the porphyrin macrocycle substituents, while half-wave potentials for the first oxidation togive a -cation radical are affected by the substituents as well as by nonplanar deformations of the porphyrinmacrocycle. The potential difference between the first and second oxidations (
Ox2 - Ox1) is highly variableamong the 29 investigated compounds and ranges from 0 mV (two overlapped oxidations) to 460 mV dependingon the macrocycle substituents and the anion of the supporting electrolyte. The magnitude of Ox2 - Ox1 isgenerally smaller for compounds with very electron-withdrawing substituents and when TBAP is used as the supportingelectrolyte. This behavior is best explained in terms of differences in the binding strengths of anions from thesupporting electrolyte (ClO4- or PF6-) to the doubly oxidized species. A closer analysis suggests two factors whichare important in modulating Ox2 - Ox1 and thus the binding affinity of the anion to the porphyrin dication. Oneis the type of -cation radical (a proxy for the charge distribution in the dication), and the other is the conformationof the porphyrin macrocycle (either planar or nonplanar). These findings imply that the redox behavior of porphyrinscan be selectively tuned to display separate or overlapped oxidation processes.
-anion radical are effected in large part by theelectronic properties of the porphyrin macrocycle substituents, while half-wave potentials for the first oxidation togive a -cation radical are affected by the substituents as well as by nonplanar deformations of the porphyrinmacrocycle. The potential difference between the first and second oxidations (Ox2 - Ox1) is highly variableamong the 29 investigated compounds and ranges from 0 mV (two overlapped oxidations) to 460 mV dependingon the macrocycle substituents and the anion of the supporting electrolyte. The magnitude of Ox2 - Ox1 isgenerally smaller for compounds with very electron-withdrawing substituents and when TBAP is used as the supportingelectrolyte. This behavior is best explained in terms of differences in the binding strengths of anions from thesupporting electrolyte (ClO4- or PF6-) to the doubly oxidized species. A closer analysis suggests two factors whichare important in modulating Ox2 - Ox1 and thus the binding affinity of the anion to the porphyrin dication. Oneis the type of -cation radical (a proxy for the charge distribution in the dication), and the other is the conformationof the porphyrin macrocycle (either planar or nonplanar). These findings imply that the redox behavior of porphyrinscan be selectively tuned to display separate or overlapped oxidation processes.