Development of Cobalt and Iron Catalysts Bearing Rigid Polydentate Ligands for Proton Reduction and C-H Bond Oxidation

The demand for energy consumption has increased exponentially since the Industrial Revolution. The major source of this energy has been and continues to be fossil fuels. The depletion of fossil fuels and environmental concerns associated with their combustion has motivated us to develop a renewable energy alternative to meet future energy demands. Hydrogen is a clean energy alternative to fossil fuels, which can be generated from solar-driven water splitting. However, more efficient and inexpensive catalysts for the hydrogen evolution reaction (HER) are needed. In this context, hydrogen production has been investigated with a stable and highly reactive cobalt-based catalyst. While petroleum and natural gas are not ideal energy sources, they are important feedstocks of inexpensive hydrocarbons for the chemical and pharmaceutical industries. The selective conversion of C-H bonds into new functional groups under mild conditions is therefore of considerable interest. High-valent nonheme iron-oxo catalysts have been developed as potent oxidants for the functionalization of unactivated C-H bonds. Likewise, the desire to further improve catalyst stability and selectivity for C-H bond oxidation encouraged us to develop and study the coordination chemistry of a polyaromatic ligand that is rigid, tetradentate, and absent of weak C-H bonds to give a strong chelate effect and high stability under strongly oxidizing conditions. The geometry, spin state, redox behavior, and other properties are analyzed for a series of first-row metal complexes