Modular Crab‐Shape Bpy‐Bisulidines, a New Class of Bifunctional <scp> <i>C</i> <sub> <i>2</i> </sub> </scp> ‐Symmetric Chiral Tetradentate Ligands and Application in Asymmetric Catalysis
Lin‐Lu Liu, Hong Cen, Dajian Pan, M. Zhang, Xifeng Zhu, Xiong‐Wei Liu, Xu‐Ting Chen, Xiong‐Li Liu
Abstract
Comprehensive Summary 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 C 2 ‐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) C 2 ‐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 C 2 ‐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.