Enantiomeric Excess Dependent Splitting of NMR Signal Through Dynamic Chiral Inversion and Co-Ligand Exchange in a Coordination Complex.

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 co-ligand, 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 co-ligand C, 2-phenoxypropionic acid (PPA). Despite the well-defined chirality in the crystal structure of L·2Zn·3C, concurrent fast chiral inversion and co-ligand 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 co-ligand exchange system. This work provides new insights into chiral transfer events in metal-ligand complexes.