Organometallic catalysts are effective in hydrogenating carbon dioxide, an over-abundant gas in our atmosphere, into a C1 fuel source. Noble metal catalysts efficiently hydrogenate CO2 to formate and methanol, but their high toxicity, cost, and danger to the environment make them less sustainable. Therefore, base-metal catalysts offer a practical solution to reduce these concerns. However there are limitations to these base-metal systems. The turnover number recorded for these systems is lower than their noble-metal counterparts, along with requiring an excessive amount of base to be efficient. Most base-metal catalyst systems that hydrogenate CO2 to C1 feedstocks contain PNP-based ligand scaffolds. Work in our group has focused on the synthesis of new PNP-style pincer ligands that utilize a 2,6-diaminopyridine backbone containing proton-responsive sulfonamide moieties that should aid in hydrogenation of CO2 and stabilization of reactive intermediates involved in catalysis. Herein we report progress on the preparation and characterization of a sterically and electronically diverse collection of PNP ligands. The PNP ligands exhibit broad 31P NMR spectra and low temperature NMR spectroscopy in concert computations were used to examine this fluxional process. In addition, we describe efforts on the synthesis and characterization of several base-metal complexes containing nickel and iron along with future efforts in catalytic reduction.

Synthesis and characterization of PNP ligands and PNP-base metal complexes containing sulfonamide groups in the secondary coordination sphere

ACS Spring 2022

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