Carbon–iodine atropisomerism on triazole and triazolium frameworks: a breathing axle with divergent adaptivity

Abstract

Atropisomerism around a carbon–iodine(III) bond represents a rare form of chirality centered on a long, polarizable hypervalent linkage. Embedding this C–I(III) bond into an inherently asymmetric, diadamantylated triazole scaffold creates a vivid platform that reveals how such a bond responds to steric and electronic perturbations. Neutral triazole- and cationic triazolium–benziodoxoles display similarly high atropostability (racemization half-lives of several years at 25 °C), arising from opposing effects introduced by N-methylation: electronic weakening of the C–I bond versus steric buttressing that restricts rotation. Under acidic conditions, however, their behaviors diverge; the triazole derivative undergoes accelerated rotation, whereas the triazolium analogue retains substantial configurational stability. The CF₃ groups of the benziodoxole ring serve as sensitive ¹⁹F NMR reporters for two complementary modes of chiral recognition. The neutral triazole engages BINOL through directional hydrogen bonding, whereas the triazolium derivative binds phosphate anions via halogen bonding and electrostatic interaction. Together, these results establish the hypervalent C–I(III) bond as a stereoelectronically tunable rotational element—an axle that enables molecular rotors combining well-defined rotational dynamics with switchable recognition behavior.