Development of Catalytic Reduction of Renewable Carbon Resources Using Well-Elaborated Organometallic Complexes with PNNP Tetradentate Ligands

The recent depletion of fossil fuel resources has impelled industrial and academic researchers to search for alternative carbon sources. Developing sustainable resources/energy is one of the most urgent missions for human beings since the increasing resources/energy demand is in drastic conflict with the limited global fossil fuel storage. In another perspective, massive production of CO2 is inevitable and the fatal risk as far as fossil resources are continuously used as the only sources of carbon. Considerable effort has been invested in biotechnology and sustainable/green technologies to develop a chemical industry in which renewable energy resources complement dwindling fossil fuel sources for the new millennium. A round-table discussion of the US Department of Energy identified the top 30 value-added chemicals derived from biomass, which included various (poly)carboxylic acids and polyols. Non-biodegradable microplastics already plague our oceans and are destroying the world. It is really no secret. These chemicals exist in high oxidation and/or highly oxygenated/nitrogenated states, and thus, current state-of-the-art oxidation catalysts must be substantially modified so that new millennium catalysts could effectively promote the reduction and dehydration of such renewable resources. We have developed new molecular technologies based on well-elaborated metal complexes with PNNP tetradentate ligands for dehydration and reduction of unactivated amides, polycarboxylic acids, and CO2 using thermal or light energy. Those catalytic systems represent potentially sustainable methods for the production of alternative energy carriers/platform chemicals on a large scale. Herein, we offer a brief account on the development of molecular insights into mononuclear low-valent transition metal complexes for reduction of a range of renewable carbon resources.