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

Carbon dioxide (CO 2 ) is a potent greenhouse gas of environmental concern. Seeking to offer a solution to the "CO 2 -problem", the chemistry community has turned a focus toward transition metal complexes which can activate, reduce, and convert CO 2 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 CO 2 activation community. These systems offer a "push-pull" style of activation where electron density is chaperoned onto CO 2 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 CO 2 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 CO 2 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 (CO 2 ) with huge potential impact.