Reversible O-O Bond Scission and O 2 Evolution at MOF-Supported Tetramanganese Clusters.

The scission of the O-O bond in O 2 during respiration and the formation of the O-O bond during photosynthesis are the engines of aerobic life. Likewise, the reduction of O 2 and the oxidation of reduced oxygen species to form O 2 are indispensable components for emerging renewable technologies, including energy storage and conversion, yet discrete molecule-like systems that promote these fundamental reactions are rare. Herein, we report a square-planar tetramanganese cluster formed by self-assembly within a metal-organic framework that reversibly reduces O 2 by four electrons, facilitating the interconversion between molecular O 2 and metal-oxo species. The tetranuclear cluster spontaneously cleaves the O-O bond of O 2 at room temperature to generate a tetramanganese-bis(μ 2 -oxo) species, which, in turn, is competent for O-O bond reformation and O 2 evolution at elevated temperatures, enabled by the head-to-head orientation of two oxo species. This study demonstrates the viability of four-electron interconversion between molecular O 2 and metal-oxo species and highlights the importance of site isolation for achieving multi-electron chemistry at polynuclear metal clusters.