Deprotonation Reactions and Electrochemistry of Substituted Open-Chain Pentapyrroles and Sapphyrins in Basic Nonaqueous Media

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• 作者：Zhongping Ou ; Deying Meng ; Mingzhu Yuan ; Wenhao Huang ; Yuanyuan Fang ; Karl M. Kadish
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：October 31, 2013
• 年：2013
• 卷：117
• 期：43
• 页码：13646-13657
• 全文大小：624K
• 年卷期：v.117,no.43(October 31, 2013)
• ISSN：1520-5207

文摘

Electrochemical and spectroelectrochemical properties of three open-chain pentapyrroles and the corresponding sapphyrins were examined in pyridine containing 0.1 M tetra-n-butylammonium perchlorate and dichloromethane (CH₂Cl₂) or benzonitrile (PhCN) containing tetra-n-butylammonium hydroxide (TBAOH). The investigated compounds are represented as (Ar)₄PPyH₃ and (Ar)₄SH₃, where Ar is a F^{鈥?/sup> or Cl鈥?/sup> substituted phenyl group, PPy is a trianion of the open-chain pentapyrrole, and S is a trianion of the sapphyrin. The pentapyrroles, (Ar)₄PPyH₃, undergo two reversible one-electron reductions in pyridine, while the structurally related sapphyrins exhibit four reductions in this solvent, the first two of which are irreversible due to coupled chemical reactions following the electron transfers. Both series of neutral compounds could be deprotonated in CH₂Cl₂ or PhCN by addition of TBAOH to solution, and the progress of these reactions was monitored as a function of the base concentration by cyclic voltammetry and UV鈥搗is spectroscopy. The neutral pentapyrroles were spectroscopically shown to undergo a loss of two protons in a single step to generate the [(Ar)₄PPyH]2鈥?/sup> dianion while the sapphyrins could only be monodeprotonated, leading to formation of the [(Ar)₄SH₂]鈭?/sup> monoanion under the same solution conditions. The deprotonation constants were measured for each series of compounds in benzonitrile, and oxidation鈥搑eduction mechanisms are examined as a function of the solution 鈥榖asicity鈥?}