Homogeneous catalysis is of prime importance for the selective synthesis of high added value chemicals. Many of the currently available catalysts rely on noble metals (Ru, Os, Rh, Ir, Pd, Pt), which suffer from a high toxicity and environmental impact in addition to their high cost, calling for the development of new systems based on first-row transition metals (Mn, Fe, Co, Ni, Cu). The historical paradigm for catalyst design, i.e. one or more donor ligands giving electron density to stabilize a metal center and tune its reactivity, is currently being challenged by the development of acceptor ligands that mostly withdraw electron density from the metal center upon binding. In the last decade, such ligands – mostly based on boron and heavier main-group elements – have evolved from a structural curiosity to a powerful tool in designing new reactive units for homogeneous catalysis.
I will develop a novel class of ligands that use C=E (E=O, S, NR) multiple bonds anchored in close proximity to the metal by phosphine tethers. The electrophilic C=E multiple bond is designed to act as an acceptor moiety that adapts its binding mode to the electronic structure of reactive intermediates with the unique additional possibility of involving the lone pairs on heteroelement E in cooperative reactivity. Building on preliminary results showing that a C=O bond can function as a hemilabile ligand in a catalytic cycle, I will undertake a systematic, experimental and theoretical investigation of the structure and reactivity of M–C–E three membered rings formed by side-on coordination of C=E bonds to a first-row metal. Their ability to facilitate multi-electron transformations (oxidative addition, atom/group transfer reactions) will be investigated. In particular, hemilability of the C=E bond is expected to facilitate challenging C–C bond forming reactions mediated by Fe and Ni. This approach will demonstrate a new conceptual tool for the design of efficient base-metal catalysts.
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