SusChEM: Water Oxidation by Homogeneous Manganese Catalysts

在这个由化学系化学合成计划资助的项目中，印第安纳大学化学和生物化学系的Jeremy M.Smith教授研究了定义明确的锰催化剂如何将水转化为氧气。大自然已经学会了利用可见光将水转化为氧气。这个过程被称为光合作用，利用复杂生物蛋白质中的锰。在这个项目中，正在研究较小的锰化合物，以提供关于光合氧形成的基本信息，并提供基于廉价、丰富的金属的新型催化剂，供实验室或化学工业使用。该项目的一个重要部分涉及对学生进行生物无机化学和能源化学的培训。本项目利用合成、光谱和物理研究来研究锰大环配合物对水的氧化机理。模块化催化剂设计允许引入官能团，从而能够系统地研究质子和氢原子传输以及金属辅助因素对催化剂性能的影响。一系列吡啶膦锰化合物作为光系统II析氧络合物的功能模型。这项工作旨在：(1)实验验证计算提出的这些络合物氧化水气的机理，(2)确定吡啶膦立体电子性质对催化选择性和活性的影响，以及(3)描述第二配位球对催化活性的影响，包括质子和氢原子继电器的存在，以及氧化还原无害金属的存在。这些物种的光谱、反应活性和机理研究提供了与生物水氧化机制相关的见解，特别是关键的O-O键形成步骤。用X射线衍射、核磁共振、电子顺磁共振和红外光谱等标准物理方法对化合物进行了表征，并结合电化学测量和标准机理探针对催化剂的催化行为进行了研究。

In this project funded by the Chemical Synthesis Program of the Chemistry Division, Professor Jeremy M. Smith, Department of Chemistry and Biochemistry, Indiana University, investigates how well-defined manganese catalysts convert water into oxygen. Nature has learned to convert water to oxygen using visible light. This process is called photosynthesis and uses manganese in a complicated biological protein. In this project, smaller managanese compounds are being studied both to provide basic information on photosynthetic oxygen formation and to provide new catalysts, based on inexpensive, abundant metals, for use in the laboratory or by the chemical industry. An important part of the project involves the training of students in bioinorganic and energy chemistry. This project utilizes synthetic, spectroscopic and physical studies to investigate the mechanism of water oxidation by manganese macrocyclic complexes. The modular catalyst design allows for the introduction of functional groups, enabling systematic studies into the effect of proton and hydrogen atom transport as well as metal cofactors on catalyst performance. A family of manganese pyridinophane compounds serve as functional models for the oxygen evolving complex of Photosystem II. This work sets out to: (1) experimentally validate a computationally-proposed mechanism for water oxidation by these complexes, (2) determine the impact of pyridinophane stereoelectronic properties on catalytic selectivity and activity, and (3) delineate the effect of the second coordination sphere on catalytic activity, including the presence of proton and hydrogen atom relays, and redox-innocent metals. Spectroscopic, reactivity and mechanistic investigations of these species provide insights relevant to the biological water oxidation mechanism, particularly the key O-O bond forming step. Compounds are characterized by standard physical methods of X-ray diffraction, NMR, EPR, and IR, while catalytic behavior is investigated by a combination of electrochemical measurements and standard mechanistic probes.