Solvent Drives Switching between ? and Δ Metal Center Stereochemistry of M8L6 Cubic Cages

An enantiopure ligand with four bidentate metal-binding sites and four (S)-carbon stereocenters self-assembles withoctahedral ZnIIor CoIIto produceO-symmetric M8L6coordination cages. The Lambda-or Delta-handedness of the metal centers forming thecorners of these cages is determined by the solvent environment: the same (S)-ligand produces one diastereomer, (S)24-Lambda 8-M8L6,inacetonitrile but another with opposite metal-center handedness, (S)24-Delta 8-M8L6, in nitromethane. Van'tHoffanalysis revealed the Delta stereochemical configuration to be entropically favored but enthalpically disfavored, consistent with a loosening of the coordinationsphere and an increase in conformational freedom following Lambda-to-Delta transition. The binding of 4,4 '-dipyridyl naphthalenediimideand tetrapyridyl Zn-porphyrin guests did not interfere with the solvent-driven stereoselectivity of self-assembly, suggestingapplications where either a Lambda-or Delta-handed framework may enable chiral separations or catalysis

Automated summary

This study found that the solvent environment plays a crucial role in determining the chirality of coordination cages formed during self-assembly, with the handedness of the metal centers being dependent on the solvent. Further analysis revealed that the Delta configuration is entropically favored but enthalpically disfavored.