Radicals in Catalysis; Selective Metal-Mediated Radical-Type Transformations

Organometallic catalysis is the cornerstone of sustainable fine-chemical transformations, but we are currently using only a limited part of its full potential. Our understanding of organometallic catalysis is primarily based on studies of closed-shell reactivity, and consequently traditional synthetic catalysis is based on diamagnetic organometallic complexes undergoing a limited number of elementary steps (oxidative-addition, reductive-elimination, insertion/deinsertion, metathesis, and transmetallation). A whole new area of open-shell organometallic catalysis has so far been almost neglected, while offering fascinating possibilities to steer and control radical-type reactions. Radicals are intrinsically reactive, and were long believed to be too reactive to be selective. However, in the coordination sphere of transition metals highly selective radical-type processes are certainly possible. In fact, radical-type reactions are tremendously important in several bio-synthetic pathways mediated by metallo-enzymes. Nature solves its most difficult and most interesting bio-synthetic problems with radical-reactivity. Yet, despite their radical-nature, these reactions proceed with ultrahigh precision and selectivity. Achieving similar selectivities in radical-type transformations employing simpler synthetic systems was long believed to be impossible, which is however an important misconception. This proposal aims at achieving high-precision catalytic radical-type reactions with synthetic organometallic catalysts, making efficient use of a combination of innovative bio-inspired enzyme-like tools. These include redox-(re)activity of ligands, metallo-radical reactivity, cooperative ligand effects and site isolation (molecular caging). These new tools will be employed in selective radical-type ring-closure-, polymerisation-, and hydrocarbon functionalization reactions. An important objective is to achieve these new reactions in an efficient and cost-effective manner. This implies selective catalytic reactions with cheap first-row transition metals. Innovative combinations of electro-synthesis and homogeneous catalysis will be explored to enable selective radical-type transformations with cheaper starting materials. Hence, the newly developed methods in this project will contribute substantially to solving long-standing efficiency and selectivity obstacles in important innovative chemical transformations.