Electrochemistry of Platinum(II) Porphyrins: Effect of Substituents and π-Extension on Redox Potentials and Site of Electron Transfer
Electrochemistry of Platinum(II) Porphyrins: Effect of Substituents and π-Extension on Redox Potentials and Site of Electron Transfer
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DOI：
10.1021/ic3003367
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发表时间：
2012-06-04
影响因子：
4.6
通讯作者：
Kadish, Karl M.
中科院分区：
文献类型：
--
作者：
Chen, Ping;Finikova, Olga S.;Kadish, Karl M.
研究了14种具有不同pi共轭大环和不同供电子或吸电子取代基的铂（II）卟啉在非水介质中的电化学和光谱性质。8个化合物的化学式为（Ar4P）Pt-II，其中Ar4P =四芳基卟啉的双离子，而6个化合物具有pi延伸的大环，具有四个β， β '-融合的苯并或萘基团，分别表示为（TBP）Pt-II和（TNP）Pt-II，其中TBP和TNP分别是四苯并卟啉和四芳基卟啉的双离子。每个Pt（II）卟啉在非水介质中经历两次可逆单电子还原和一到三次可逆单电子氧化。这些反应用循环伏安法、紫外可见薄层光谱电化学和ESR光谱进行了表征。这两种还原总是发生在共轭pi-环体系中，以产生相对稳定的Pt(II) pi-阴离子自由基和阴离子。第一次氧化导致所研究的卟啉形成稳定的阳离子自由基；但对于含有吸电子取代基的四芳基卟啉，第二次氧化的产物可能发生内部电子转移，得到具有未氧化大环的Pt（IV）卟啉。讨论了大环结构对紫外可见光谱、氧化还原电位和电子转移位置的影响。
Fourteen platinum(II) porphyrins with different pi-conjugated macrocycles and different electron-donating or electron-withdrawing substituents were investigated as to their electrochemical and spectroscopic properties in nonaqueous media. Eight compounds have the formula (Ar4P)Pt-II, where Ar4P = the dianion of a tetraarylporphyrin, while six have pi-extented macrocycles with four beta,beta'-fused benzo or naphtho groups and are represented as (TBP)Pt-II and (TNP)Pt-II where TBP and TNP are the dianions of tetrabenzoporphyrin and tetranaphthoporphyrin, respectively. Each Pt(II) porphyrin undergoes two reversible one-electron reductions and one to three reversible one-electron oxidations in nonaqueous media. These reactions were characterized by cyclic voltammetry, UV-visible thin-layer spectroelectrochemistry and in some cases by ESR spectroscopy. The two reductions invariably occur at the conjugated pi-ring system to yield relatively stable Pt(II) pi-anion radicals and dianions. The first oxidation leads to a stable pi-cation radical for each investigated porphyrin; but in the case of tetraarylporphyrins containing electron-withdrawing substituents, the product of the second oxidation may undergo an internal electron transfer to give a Pt(IV) porphyrin with an unoxidized macrocycle. The effects of macrocycle structure on UV-visible spectra, oxidation/reduction potentials, and site of electron transfer are discussed.