This project aimed at the development of new organic molecules (ligands) that bind transition metal atoms and modify their chemical properties so that they can serve as catalysts, that is facilitate effective chemical transformations for the synthesis of chemicals.
Currently, both research labs and industrial production plants make extensive use of noble metals (Palladium, platinum, Rhodium, Iridium,...) for catalysis. These are efficient, but associated with a high monetary and environmental cost as their extraction is energy intensive and their concentration in waste streams is potentially detrimental to the environment. It would be advantageous to be able to use the more abundant, less expensive, sometimes less toxic metals of the first transition series (Iron, Cobalt, Nickel) instead. However, the reactivity of latter have proven more difficult to control, yielding often inefficient or unselective processes.
To tackle this problem, we synthesized new organic molecules that can cooperate with such metal centers to activate organic molecules and achieve catalytic transformations. Specifically, we used ligands that incorporate multiple bonds (C=E, where E is N, O, C, and B=N) as a reactive cooperative site. Because the interaction between the multiple bond and the metal is labile, our ligands incorporate two "arms" terminated with a strongly-binding phosphorus atom that anchor the reactive site to the metal. For comparison, an analogous ligand containing a third phosphorus atom instead of a multiple bond was included in the study. We investigated the binding of these "pincer" ligands to earth-abundant metals and the reactivity of the formed complexes with small molecules such as Hydrogen, Silanes, aromatic compounds. We evaluated the produced molecules in industrially relevant catalytic reactions including C–C cross coupling and hydrogenation and characterized their mode of action in details using both experimental and theoretical methods. These findings will inform further development of new catalysts, both in our own labs and in the broader scientific community.
