Characterization of molecular cobalt complexes relevant to electrocatalytic CO_2 & H^+ reduction

Abstract

Certain mol. cobalt complexes are competent in electrocatalytic transformations such as CO_2 and /or H+ redn. While interesting from a purely chem. standpoint, these systems have also found interest because of their relevance to solar- energy related chem. transformations. The desire to lower the overpotentials necessary to achieve meaningful current densities has encouraged our investigations into the chem. and structural properties of the reduced compds. that are proposed to be involved in key mechanistic steps in hopes to gain insight into future catalyst design. In a typical proposed electrocatalytic mechanism, intermediates such as Co- CO_2 adducts or Co(III) - hydride complexes are invoked and are synthetic targets for our studies. We have synthesized compds. with N_4 macrocyclic ligands that contain intra- mol. H- bond donors and /or phosphine ligands in hopes to stabilize CO_2 adducts and hydride ligands bound to cobalt centers. Combined spectroscopic, X- ray structural, and reactivity studies provide insights into the properties of these compds. and will be discussed herein. Specifically, we have conducted a structure function study on an N_4 macrocyclic ligand with an N- H moiety that may be involved in stabilizing a CO_2 adduct that is subsequently reduced to form carbon monoxide in aq. acetonitrile. We have also prepd. another N_4 - macrocylcic cobalt complex that contains an axial phosphine ligand and have investigated putative hydride intermediates on this platform.

Additional details