Probing achiral benzene-1,3,5-tricarboxamide monomers as inducers of homochirality in supramolecular helical catalysts

Adding a complementary achiral monomer to macromolecules embedding a mixture of enantiopure monomers (the “sergeants”) and achiral monomers (the “soldiers”) is expected to decrease the optical purity of the polymer main chain because of the dilution of the sergeant in the thus generated terpolymer. Herein, we report the influence of such achiral benzene-1,3,5-tricarboxamide (BTA) additives on the structural, chiroptical and catalytic properties of “sergeants-and-soldiers” mixtures composed of an achiral BTA ligand coordinated to copper and of an enantiopure BTA monomer derived from cyclohexylalanine. Whilst N,N’,N’’-tris(octyl)benzene- 1,3,5-tricarboxamide (BTA C8) shows no significant improvement in term of enantioselectivity in the catalytic reaction of reference, achiral BTA monomers derived from ,’-disubstituted amino esters all lead to an increase in the selectivity at low “sergeant” ratio. This different behaviour was probed by characterizing the coassemblies embedding BTA C8, i.e. the worst-performing achiral additive, and the BTA derived from the ester of 1-aminocyclohexane carboxylic acid (BTA Achc), the best-performing one. Both additives were found to efficiently intercalate with the ligand and the “sergeant” leading to the formation of single helices. However, only the terpolymer embedding BTA Achc exhibits a cooperative assembly behaviour that leads to long, stable, and homochiral coassemblies, accounting for the good enantioselectivity even at very low “sergeant” ratio (0.25%). This study also reveals the possibility to tune the nature of the achiral additive and its amount relatively to the pristine coassemblies for achieving a good compromise between the extent of the “sergeants-and-soldiers” effect and the optimal enantioselectivity displayed by the catalytic terpolymers.