The Chemistry of Two-Electron Mixed Valence Excited States

无机化学、生物无机化学和金属有机化学项目的这一奖项支持麻省理工学院化学系的Daniel G.Nocera博士对两电子转移反应的研究。这项研究的目的是阐明光活化金属中心发生双电子步骤氧化还原反应的激发态反应途径。每个研究的络合物都将包含两个不同氧化状态的金属原子，通过单一或多个金属-金属键连接。在单一金属-金属键合物种的情况下，金属的氧化状态有两个不同。例如，由二氟膦配体桥联的卤化氢中二氢或二卤素的光消除有望通过可以表征的Rh2(II，0)混合价中间体进行。还将合成和研究更多的配合物，包括那些含有不对称配体以稳定两电子混合价态中心的配合物。在二聚体通过多个键连接的情况下，通过光产生具有M-M+特性的核可以实现两电子的混合价。这种物种可以从具有四个键或具有共享边的生物八面体排列的络合物中获得。多电子反应发生在许多重要的过程中，包括光催化、能量转换和信息处理。这里研究的反应是不寻常的，因为一个光子促进了两个电子的运动。了解多电子转移的机制应该会为涉及过渡金属和小分子光转化的新反应开辟道路。参与该项目的学生将体验合成技术和物理方法。

This award in the Inorganic, Bioinorganic, and Organometallic Chemistry Program supports research on two-electron transfer reactions by Dr. Daniel G. Nocera of the Chemistry Department, Massachusetts Institute of Technology. The goal of the research is to elucidate excited state reaction pathways for oxidation-reduction reactions occurring in two-electron steps at photoactivated metal centers. Each complex studied will contain two metal atoms in different oxidation states, linked by either single or multiple metal-metal bonds. In the case of single metal-metal bonded species, the oxidation states of the metals differ by two. For example, photoelimination of dihydrogen or dihalogen from hydrido halides of dirhodium bridged by difluorophospine ligands is expected to proceed through a Rh2(II,0) mixed valence intermediate that can be characterized. Additional complexes, including ones containing asymmetric ligands to stabilize the two-electron mixed valence centers, will be synthesized and studied. In the case of dimers linked by multiple bonds, two-electron mixed valency will be achieved by photogenerating a core with M-M+ character. Such species can be obtained from complexes with quadruple bonds or with an edge-sharing bioctahedral arrangement. Photoinitiated bond addition and atom transfer reactions for a variety of substrates will be explored.Multielectron reactions are not well understood, but occur in many important processes, including photocatalysis, energy conversion, and information processing. The reactions studied here are unusual in that one photon promotes the movement of two-electrons. Understanding the mechanism of multielectron transfer should open the way to new reactions involving transition metals and small molecule phototransformations. Students involved in the project will experience both synthetic techniques and physical methods.