Evaluation of Zn2+ Coordination Structures in Chiral Zn2+ Complexes Based on Shape Measurement Factors: Relationships between Activity and the Coordination Structure.

Autor: Aoki, Shin, Kikuchi, Chiharu, Kitagawa, Yuichi, Hasegawa, Yasuchika, Sonoike, Shotaro, Saga, Yutaka, Hatanaka, Miho
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Zdroj: European Journal of Inorganic Chemistry; 11/30/2019, Vol. 2019 Issue 44, p4740-4751, 12p
Abstrakt: We previously reported on enantioselective aldol reactions of acetone and cyclic ketones with benzaldehyde derivatives catalyzed by chiral Zn2+ complexes that mimic class II aldolases. The results and mechanistic studies indicated that the catalytic activity of Zn2+ complexes is dependent not only on the coordination numbers of Zn2+ but also on its coordination structure. In this study, we report on shape measures (abbreviated as S values in this manuscript) of such Zn2+ complexes with respect to the 5‐coordination structure based on calculations with continuous shape measures (CShM) using their crystal structures. The S values of Zn2+ ions in Zn2+ complexes for trigonal bipyramidal (D3h) or square pyramidal (C4v) structures suggest that Zn2+ ions in the catalytically active Zn2+ complexes possess D3h and C4v structures, while Zn2+ ions in the unreactive Zn2+ complex has a C4v structure. Moreover, the S values of Zn2+ were calculated with respect to 6‐coordination geometry, based on the assumption that aldol reactions proceed via 6‐membered transition states, and it was implied that 6‐coordinated Zn2+ ions in aldol‐active Zn2+ complexes prefer an octahedron structure (Oh). These results for the S values of Zn2+ ions in the active Zn2+ complexes and those for complexes reported by other research groups suggest that the transition of 5‐coordinated D3h to the 6‐coordinated Oh structure is essential for achieving catalytic stereoselective aldol reactions. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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