A Blueprint for Secondary Coordination Sphere Editing: Approaches Toward Lewis‐Acid Assisted Carbon Dioxide Co‐Activation

The reduction of carbon dioxide (CO₂) to value-added products is top-of-mind. In this arena, chemists are well-positioned to lead the charge. Herein, we present advances made in homogeneous CO₂ reduction using transition metal/Lewis-acid systems, with a focus on installing Lewis-acids into the primary or secondary coordination sphere of the ligand framework.

Abstract

Carbon dioxide (CO₂) is a potent greenhouse gas of environmental concern. Seeking to offer a solution to the “CO₂-problem”, the chemistry community has turned a focus toward transition metal complexes which can activate, reduce, and convert CO₂ into carbon-based products. The design of such systems involves judicious selection of both metal and accompanying donor ligand; in part, these efforts are motivated by biological metalloenzymes that undertake similar transformations. As a design element, metal-ligand cooperativity, which leverages intramolecular interactions between a transition metal and an adjacent secondary ligand site, has been acknowledged as a vitally important component by the CO₂ activation community. These systems offer a “push-pull” style of activation where electron density is chaperoned onto CO₂ with an accompanying electrophile, such as a Lewis-acid, playing the role of acceptor. This pairing allows for the stabilization of reactive C _x H _y O _z -containing intermediates and can bias CO₂ product selectivity. In the laboratory, chemists can test hypotheses and ideas, enabling rationalization of why a given pairing of transition metal/Lewis-acid leads to selective CO₂ reduction outcomes. This Concept identifies literature examples and highlights key design properties, allowing interested contributors to design, create, and implement novel systems for productive transformations of a small molecule (CO₂) with huge potential impact.

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