Earth-Abundant metals with exclusively achiral ligands for sustainable chiral-at-metal catalysis
Asymmetric catalysis relies on the design of chiral catalysts and is dedicated to the economical generation of non-racemic chiral compounds, which are building blocks for the production of drugs, agricultural chemicals, flavors, fragrances, and materials. Chiral transition metal complexes constitute an important class of chiral catalysts and are typically synthesized by combining metal salts or organometallic precursors with chiral ligands. A neglected approach follows a different direction and exploits the generation of metal-centered chirality in the course of the assembly of achiral ligands around a central metal. Our group has pioneered the general use of such chiral-at-metal catalysts from noble metals, with the metal center both serving as the exclusive stereogenic center and at the same time acting as the reactive center for catalysis. The design of reactive chiral-at-metal catalysts based on earth-abundant metals, which have economical and environmental benefits, is the focus of this proposal. The design strategy appeals for its combination of sustainability (earth-abundant metals) and simplicity (achiral ligands). Furthermore, without the requirement for chiral motifs in the ligand sphere, untapped opportunities emerge for the design of chiral 3d metal complexes with distinct electronic properties and unique architectures. This unexplored chemical space for chiral catalysts will be applied to the challenging enantioselective functionalization of C(sp3)-H bonds with inexpensive and sustainable 3d metal catalysts.
The implementation of chiral-at-metal catalysts from earth-abundant metals will rely on taming the high lability of coordinative bonds of 3d metals to warrant a satisfactory configuration stability. This will be addressed by exploiting the chelate effect of tailored multidentate ligands in combination with strong-field ligands and attractive weak interactions between coordinated ligands.