Metal-ligand cooperativity at nickel π-complexes for the stabilization of reactive intermediates and hydrogenation catalysis

Abstract

As the chemical industry is one of the largest and most impactful industrial sectors, chemistry research plays a determining role in the transition towards a sustainable world. To this end, the 12 principles of Green Chemistry are an important guide in the design of new chemical processes, focusing on minimizing (or eliminating) the use and generation of hazardous substances. The “Catalysis vs. Stoichiometric” principle establishes the key role of catalysts, as using them in small amounts can accelerate a chemical reaction. Generally, catalytic processes occur in a selective manner, involving less resources and generating less waste. In line with this principle, this thesis focuses on the development of the catalytic potential of nickel, an earth-abundant metal, bound to phosphorus-based organic ligands bearing an unsaturated C=X (X = C, O or N) moiety. Our approach involved two different lines. First, the diverse transformations of a crucial “nickelacyclobutane” reactive intermediate were investigated to better understand and control the selectivity of catalytic reactions. The obtained results show that nickel intermediates can undergo selective reactivity in processes traditionally done by expensive precious metals. Second, an unusual mechanism for H–H and C–H bond activation using an olefin-nickel complex was discovered, and its utility for catalytic hydrogenation was demonstrated. These results bring new insight into how metal complexes catalyze hydrogenation reactions and provides a basis for the development of a new family of sustainable catalysts.