Combining Metal-Metal and Metal-Ligand Cooperativity: Homomultimetallic complexes of copper, iron and ruthenium

Abstract

By far most of chemical products are produced using a catalysts. Catalysts are able to accelerate chemical reactions, can give high selectivity to one or a few (desired) products, often require less energy for the reaction and minimizes waste production. Soluble catalyst, so called homogeneous catalysts, are often used for the synthesis of large, complex molecules, such as pharamceuticals. These homogeneous catalysts often are metal complexes, which are compounds that have a molecule, called a ligand, bound to a metal atom or ion. Most man-made effective catalysts rely on scarce and expensive precious metals. However, in nature many challenging chemical transformations are performed by multiple abundant metal atoms inside proteins that behave as large metal complexes. This is possible by these enzymes because of several concepts, of which two are metal-metal cooperativity and metal-ligand cooperativity, which means that mulitple metals work together to break and make chemical bonds and that the ligand also assists the metal in this process. Many modern metal complex catalysts use metal-ligand cooperativity or metal-metal cooperativity, but not both. This work describes the synthesis of various multimetallic complexes of copper, iron and ruthenium with the metals close to each other, which can enable both metal-ligand and metal-metal cooperativity. These new classes of molecules are used to study different catalytic reaction among which are the azide-alkyne cylcoaddition reaction, selective hydogenation of alkynes to trans-alkenes and electrochemical hydrogen production. We show that these multimetallic catalysts can give a unique selectivity for a certain product or provide a different mechanistic route compared to other catalysts, which can be a starting point for discovering new chemical reactions or products from a certain reaction.