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

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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.