Asymmetric construction of tetrahedral chiral zinc with high configurational stability and catalytic activity

• Published in: Nature communications Vol. 11; no. 1; p. 6263
• Main Authors: Endo, Kenichi, Liu, Yuanfei, Ube, Hitoshi, Nagata, Koichi, Shionoya, Mitsuhiko
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.12.2020; Nature Publishing Group; Nature Portfolio
• Subjects: 140/131; 140/58; 639/638/263; 639/638/549/884; 639/638/911; Absolute configuration; Asymmetry; Benzene; Catalysts; Catalytic activity; Chirality; Construction; Coordination compounds; Crystallization; Diels-Alder reactions; Enantiomers; Humanities and Social Sciences; Ligands; Metal complexes; multidisciplinary; Optical materials; Racemization; Science; Science (multidisciplinary); Stability; Substitution reactions; Yield; Zinc; Zinc compounds
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-020-20074-7

Chiral metal complexes show promise as asymmetric catalysts and optical materials. Chiral-at-metal complexes composed of achiral ligands have expanded the versatility and applicability of chiral metal complexes, especially for octahedral and half-sandwich complexes. However, Werner-type tetrahedral complexes with a stereogenic metal centre are rarely used as chiral-at-metal complexes because they are too labile to ensure the absolute configuration of the metal centre. Here we report the asymmetric construction of a tetrahedral chiral-at-zinc complex with high configurational stability, using an unsymmetric tridentate ligand. Coordination/substitution of a chiral auxiliary ligand on zinc followed by crystallisation yields an enantiopure chiral-only-at-zinc complex (> 99% ee). The enantiomer excess remains very high at 99% ee even after heating at 70 °C in benzene for one week. With this configurationally stable zinc complex of the tridentate ligand, the remaining one labile site on the zinc can be used for a highly selective asymmetric oxa-Diels-Alder reaction (98% yield, 87% ee) without substantial racemisation. Unlike traditional chiral metal complexes, which typically contain chiral ligands, in chiral-at-metal complexes chirality originates from a stereogenic metal center bound to achiral ligands. Herein, the authors use an unsymmetric tridentate ligand to construct a Werner-type tetrahedral chiral-at-zinc complex which displays high configurational stability and catalyzes an oxa-Diels-Alder reaction with high yield and enantioselectivity.