Study of the Cooperative Effect of Two or More Metal Centers in the Metal-Oxo Mediated O-OBond Formation and Cleavage Steps

自然界经常使用多核金属活性位点，包括锰、铁和铜等廉价而丰富的金属，以实现水的氧化、甲烷羟基化或四电子还原双氧为水等重要功能。金属-氧介导的O-O键形成和裂解反应是这些过程的组成部分。基于廉价和丰富材料的同样高效的人工催化剂引起了极大的兴趣。然而，迄今为止已知的用于上述过程的分子催化剂数量相对较少，其中大多数是基于昂贵的第二和第三行过渡金属。此外，在大多数情况下，已知的化合物是一种预催化剂，而催化活性的确切种类还没有很好地确定。为了设计进一步改进的催化剂，有很大的动力来充分表征现有配合物的活性物种，包括所有相关的高氧化态、中间体和过渡态，从而建立它们影响小分子活化的机制。为了深入了解金属介导的小分子活化过程中两个或多个金属中心的协同效应，我们建议合成一系列具有生物相关性的过渡金属如Fe， Co， Ni和Cu的多核配合物，其中体系的核数将系统地从2到6不等。在O-O键形成和解理过程中，涉及不同金属中心和核的配合物的反应性将被比较，并特别强调反应中间体的分离。我们将对活性中间体进行详细的光谱表征，并对它们的反应性和理论进行研究，这将有助于我们建立被捕获中间体的结构-功能相关性。这种结合了光谱和计算方法的方法，可以为设计有效的催化剂提供必要的先决条件，这些催化剂用于在环境条件下使用便宜且容易获得的第一排过渡金属来选择性官能化非活化的C-H键、双氧还原或水氧化。

Nature often employs polynuclear metal active sites involving cheap and abundant metals like manganese, iron and copper to achieve vital functions like oxidation of water, methane hydroxylation, or the four electron reduction of dioxygen to water. Metal-oxo mediated O-O bond formation and cleavage reactions are integral part of these processes. Artificial catalysts that are similarly efficient and based on inexpensive and abundant materials are of great interest. However, only a relatively small number of molecular catalysts for the above processes are hitherto known, with the majority of them being based on expensive second and third row transition metals. Moreover, in most cases the known compound is a precatalyst and the precise species responsible for catalytic activity is not well established. To engineer further improved catalysts, there is a substantial impetus to characterize fully the active species of existing complexes, including all relevant higher oxidation states, intermediates, and transition states, so as to establish the mechanism(s) by which they affect activation of small molecules. In the context of obtaining detailed insights into the synergic effect of two or more metal centers during the metal-mediated activation of small molecules, we propose to synthesize a series of multinuclear complexes of biologically relevant transition metals like Fe, Co, Ni and Cu, where the nuclearity of the system will be systematically varied from 2 to 6. The reactivity of the complexes involving different metal centers and nuclearity in O-O bond formation and cleavage processes will then be compared with particular emphasis on the isolation of reactive intermediates. A detailed spectroscopic characterization of the reactive intermediates will be undertaken together with their reactivity and theoretical studies, which will help us to establish a structure-function correlation for the trapped intermediates. This combined spectroscopic and computational approach, may allow vital insights into the prerequisites necessary for the design of efficient catalysts for the selective functionalization of unactivated C-H bonds, dioxygen reduction, or water oxidation by using cheap and readily available first row transition metals under ambient conditions.