Department of Chemistry , Indian Institute of Technology Roorkee , Roorkee 247667 , India.
Department of Chemistry , University of Houston , Houston , Texas 77204-5003 , United States.
Inorg Chem. 2020 Jan 21;59(2):1481-1495. doi: 10.1021/acs.inorgchem.9b03329. Epub 2019 Dec 31.
The electrochemical and physicochemical properties of tetraphenylporphyrins and tetraphenylchlorins with two fused indanedione (IND) or malononitrile (MN) groups and two antipodal Br, Ph, or H β-substituents are investigated in nonaqueous media. These compounds were synthesized by oxidative fusion of free-base -chlorins, followed by metalation. The corresponding free-base di-fused chlorins were also isolated as intermediates and characterized for comparisons. The examined di-fused porphyrins (DFP) and di-fused chlorins (DFC) are represented as MDFP(Y)(R) and HDFC(Y)(R), where M = 2H, Cu, Ni, Zn, and Co, Y is a fused indanedione (IND) or malononitrile group (MN), and R = H, Br, or Ph. The IND- and MN-appended compounds in both series exhibit the expected two one-electron oxidations but quite different redox behavior is observed upon reduction, where the free-base IND-appended chlorins show four reversible one-electron reductions, compared to only two for the related free-base MN-appended chlorins. Although porphyrin trianions and tetraanions have been recently described for derivatives with highly electron-withdrawing and/or π-extending substituents, this seems not to be the case for the doubly fused IND-chlorins, where the first two one-electron additions are proposed to be located at the conjugated macrocycle and the last two at the fused IND groups, each of which is reduced at a different potential, consistent with the behavior expected for two equivalent and interacting redox centers. Unlike the examined chlorins, which are all stable in their electroreduced forms, the electrogenerated anionic forms of the di-fused porphyrins are all highly reactive and characterized by cyclic voltammograms having reduction peaks not only for the synthesized compounds added to solution but also for one or more new redox active species formed at the electrode surface in homogeneous chemical reactions following electron transfer. Comparisons are made between electrochemical behavior of the structurally related porphyrins and chlorins and the sites of electron transfer assigned on the basis of known electrochemical diagnostic criteria. One of the compounds, ZnDFP(MN), was also structurally characterized as having a ruffled and twisted macrocyclic conformation.
在非水介质中研究了具有两个融合的茚二酮（IND）或丙二腈（MN）基团和两个对映体 Br、Ph 或 Hβ-取代基的四苯基卟啉和四苯基氯的电化学和物理化学性质。这些化合物是通过游离碱卟啉和氯的氧化融合，然后进行金属化合成的。还分离出相应的游离碱双融合氯作为中间体进行比较。所研究的双融合卟啉（DFP）和双融合氯（DFC）表示为 MDFP（Y）（R）和 HDFC（Y）（R），其中 M = 2H、Cu、Ni、Zn 和 Co，Y 是融合的茚二酮（IND）或丙二腈基团（MN），R = H、Br 或 Ph。这两个系列中的 IND 和 MN 取代的化合物都表现出预期的两个单电子氧化，但观察到的还原行为却大不相同，其中游离碱 IND 取代的氯显示出四个可逆的单电子还原，而相关的游离碱 MN 取代的氯只有两个。尽管最近已经描述了具有高吸电子和/或π扩展取代基的衍生物的卟啉三阴离子和四阴离子，但对于双融合 IND-氯来说似乎并非如此，其中前两个单电子加成被提议位于共轭大环上，而最后两个位于融合的 IND 基团上，每个基团都在不同的电位下还原，这与预期的两个等效且相互作用的氧化还原中心的行为一致。与所有在其电还原形式中稳定的被研究的氯不同，双融合卟啉的电生成阴离子形式都是高度反应性的，并且其循环伏安图表现出不仅对于添加到溶液中的合成化合物而且对于在电极表面上形成的一个或多个新的氧化还原活性物质的还原峰，这些物质在电子转移后通过均相化学反应形成。比较了结构相关的卟啉和氯的电化学行为以及根据已知电化学诊断标准分配的电子转移位置。其中一种化合物 ZnDFP（MN）也被结构表征为具有起皱和扭曲的大环构象。
