Kadish Karl M, Frémond Laurent, Burdet Fabien, Barbe Jean-Michel, Gros Claude P, Guilard Roger
Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA.
J Inorg Biochem. 2006 Apr;100(4):858-68. doi: 10.1016/j.jinorgbio.2006.01.010. Epub 2006 Mar 3.
A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O(2) to H(2)O and/or H(2)O(2) when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1M HClO(4). The examined compounds are represented as (PCY)M(III)ClCo(IV)Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H(2)Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co(2) which were shown to efficiently electrocatalyze the four electron reduction of O(2) at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co(2), (PCY)H(2)Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O(2) electroreduction at potentials more positive by an average 110mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E(1/2) values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co(2) and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H(2)Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co(2) contains a Co(II) porphyrin and a Co(IV) corrole.
一系列异双核共面卟啉 - 咕啉二元化合物，其中含有一个通过四种不同间隔基之一以面对面排列方式与铁（III）或锰（III）卟啉相连的钴（IV）咕啉，已被研究作为在含有1M高氯酸的空气饱和水溶液中吸附在石墨电极表面时将O(2)电还原为H(2)O和/或H(2)O(2)的催化剂。所研究的化合物表示为(PCY)M(III)ClCo(IV)Cl，其中P是卟啉二价阴离子，C是咕啉三价阴离子，Y是联亚苯基（B）、9,9 - 二甲基呫吨（X）、二苯并呋喃（O）或蒽（A）间隔基。一方面，将这七种研究的二元化合物在两种异双金属(PCY)MClCoCl系列催化剂中的催化行为与先前报道的具有单个钴（III）咕啉大环与具有相同连接桥集合的游离碱卟啉相连的相关二元化合物(PCY)H(2)Co进行比较，另一方面与形式为(PCY)Co(2)的二钴卟啉 - 咕啉二元化合物进行比较，后者已被证明在酸性介质中能在石墨电极上有效地电催化O(2)的四电子还原。卟啉 - 咕啉二元化合物的四个系列(PCY)Co(2)、(PCY)H(2)Co、(PCY)FeClCoCl和(PCY)MnClCoCl之间的比较表明，在所有情况下，与含有与游离碱金属卟啉或具有铁（III）或锰（III）中心金属离子的金属卟啉相连的钴（III）或钴（IV）咕啉大环的相关系列化合物相比，二钴二元化合物催化O(2)电还原的电位平均更正110mV。数据表明，电催化开始的E(1/2)值与电子转移的起始位点有关，在(PCY)Co(2)的情况下是钴（III）/钴（II）卟啉还原过程，在(PCY)MnClCoCl、(PCY)FeClCoCl和(PCY)H(2)Co的情况下是钴（IV）/钴（III）咕啉还原。总体数据还表明，(PCY)Co(2)中二钴二元化合物的催化活性形式包含一个钴（II）卟啉和一个钴（IV）咕啉。
