Absence of Non‐Linear Effects Despite Evidence for Catalyst Aggregation

An in-depth study of the catalytic system, consisting enantioselective addition ZnEt2 to benzaldehyde with (1R,2S)-(−)-N-Methylephedrine (NME) as chiral ligand, suggests presence dimeric and trimeric aggregates, deduced from product ee vs. catalyst loading NMR investigations (1H, DOSY). Formation aggregation was excluded in earlier studies this system displays a linear ligand ee-correlation, which is usually taken an indication for absence aggregation. A subsequent theoretical study, using monomer-dimer competition model, we have recently developed, highlights possible parameter configurations leading plots – despite dimers. It shows that, while Kagan Noyori models allow linearity very specific cases only, multitude scenarios may lead here, especially if heterochiral dimers are catalytically active.