Modular Crab-Shape Bpy-Bisulidines, a New Class of Bifunctional C₂-Symmetric Chiral Tetradentate Ligands and Application in Asymmetric Catalysis

Abstract

Chiral bipyridines represent a class of ligands noted for their distinctive reactivity and stereoselectivity in metal-catalyzed reactions. Herein, we have developed a new class of bifunctional C₂-symmetric chiral bipyridine-type tetradentate ligands, abbreviated as Bpy-Bisulidines. These crab-shape ligands feature that: (1) bipyridine framework possesses the rich coordination ability with various metal ions; (2) chiral imidazolidine could generate a deep chiral pocket; (3) C₂-symmetry could reduce the number of possible transition states; (4) rigid chiral enviroments are close to the metal, and (5) imidazolidine N-H moiety acts as hydrogen-bonding donor. The newly developed chiral Bpy-Bisulidine ligands were successfully applied in Ni(II)-catalyzed asymmetric Friedel-Crafts alkylation reaction and inverse-electron-demand Hetero-Diels-Alder reactions, achieving excellent stereoselectivities. Our work is the first example of bifunctional C₂-symmetric chiral imidazolidine-type tetradentate ligands. X-ray crystallographic analysis of the Bpy-Bisulidine-Ni(OTf)₂ complex, control experiments and linear correlation showed that the catalytically active species was a monomeric catalyst.

Keywords

Bpy-bisulidines / Crab-shape / Modular synthesis / Tetradentate ligands / C₂-Symmetric / Rigid / Synthesis design / Heterocycles

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