Enantiomeric Excess Dependent Splitting of NMR Signal through Dynamic Chiral Inversion and Coligand Exchange in a Coordination Complex

Takimoto, Kazuyoshi; Ishihara, Shinsuke; Labuta, Jan; Březina, Václav; Payne, Daniel T.; Hill, Jonathan P.; Ariga, Katsuhiko; Sumita, Masato; Mori, Shigeki and Sato, Hisako (2020). Enantiomeric Excess Dependent Splitting of NMR Signal through Dynamic Chiral Inversion and Coligand Exchange in a Coordination Complex. The Journal of Physical Chemistry Letters, 11(19) pp. 8164–8169.

DOI: https://doi.org/10.1021/ACS.JPCLETT.0C02284

Abstract

Nuclear magnetic resonance (NMR) spectroscopy cannot be used to discriminate enantiomers, and NMR resonances of enantiomeric mixtures are generally not affected by enantiomeric excess (ee). Here, we report that a coordination complex (L·2Zn·3C), where L is a salen-like prochiral ligand and C is an exchangeable acetate coligand, exhibits symmetrical splitting of one of the 1H NMR resonances of L with the degree of splitting linearly proportional to ee of the chiral guest coligand C, 2-phenoxypropionic acid. Despite the well-defined chirality in the crystal structure of L·2Zn·3C, concurrent fast chiral inversion and coligand exchange in solution renders L·2Zn·3C the primary example of prochiral solvating agent (pro-CSA) based on a coordination complex. Notably, the NMR resonances remain split even in dilute solution due to the lack of chiral guest dissociation in the coligand exchange system. This work provides new insights into chiral transfer events in metal–ligand complexes.

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