A Mechanistic Dichotomy in Two‐Electron Reduction of Dioxygen Catalyzed by N,N’‐Dimethylated Porphyrin Isomers
A Mechanistic Dichotomy in Two‐Electron Reduction of Dioxygen Catalyzed by N,N’‐Dimethylated Porphyrin Isomers
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N,N-二甲基化卟啉异构体催化双氧双电子还原的机理二分法
DOI：
10.1002/chem.202000942
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发表时间：
2020
影响因子：
4.3
通讯作者：
Takahiko Kojima
中科院分区：
文献类型：
--
作者：
Wataru Suzuki;Hiroaki Kotani;Tomoya Ishizuka;Takahiko Kojima
二氧（O2）选择性双电子还原为过氧化氢（H2O2），采用两种鞍形扭曲的dn，N ' -二甲基化卟啉异构体，anN21,N ' 22 -二甲基化卟啉（anti - Me2P）和anN21，N ' 23 -二甲基化卟啉（syn - Me2P）作为催化剂和二茂铁衍生物作为电子供体，在乙腈中存在质子酸。在氧还原反应（ORR）中，anti - Me2P具有更高的催化性能，其周转数（TON=250，持续30分钟）高于syn - Me2P（TON=218，持续60分钟）。催化ORR中的反应中间体经光谱测定证实为相应的异叶绿素（anti - Me2Iphorsyn - Me2Iph）。基于动力学分析，认为催化orr反应的速率决定步骤是质子偶联电子转移还原o2与异氯酚。根据观察到的初始速率对酸浓度的依赖性判断，外部质子加速了anti - me2iphr的ORR速率。相比之下，没有观察到syn - Me2Iphby外质子加速ORR速率。这两种同分异构体对o2的还原机制的不同应归因于o2与异氯酚内氢质子的氢键排列的不同。
Selective two‐electron reduction of dioxygen (O2) to hydrogen peroxide (H2O2) has been achieved by two saddle‐distortedN,N’‐dimethylated porphyrin isomers, anN21,N’22‐dimethylated porphyrin (anti‐Me2P) and anN21,N’23‐dimethylated porphyrin (syn‐Me2P) as catalysts and ferrocene derivatives as electron donors in the presence of protic acids in acetonitrile. The higher catalytic performance in an oxygen reduction reaction (ORR) was achieved byanti‐Me2Pwith higher turnover number (TON=250 for 30 min) than that bysyn‐Me2P(TON=218 for 60 min). The reactive intermediates in the catalytic ORR were confirmed to be the corresponding isophlorins (anti‐Me2Iphorsyn‐Me2Iph) by spectroscopic measurements. The rate‐determining step in the catalytic ORRs was concluded to be proton‐coupled electron‐transfer reduction of O2with isophlorins based on kinetic analysis. The ORR rate byanti‐Me2Iphwas accelerated by external protons, judging from the dependence of the observed initial rates on acid concentrations. In contrast, no acceleration of the ORR rate withsyn‐Me2Iphby external protons was observed. The different mechanisms in the O2reduction by the two isomers should be derived from that of the arrangement of hydrogen bonding of a O2with inner NHprotons of the isophlorins.