Synthesis of optically active polymers containing a main-chain hydroxamic acid backbone via asymmetric polymerization

Abstract

Hydroxamic acids are versatile functional motifs that form stable chelates with transition-metal ions and serve as chiral ligands in catalytic systems. Here we report the synthesis of a novel optically active polymer incorporating hydroxamic acid units into its main chain via asymmetric polymerization and post-polymerization conversion. The asymmetric polymerization of an achiral bifunctional monomer catalyzed by a planar-chiral ruthenium complex, followed by a thiol–ene reaction and deprotection of the p-alkoxybenzyl group, afforded the desired polymer, maintaining the chiral environment, as confirmed by UV and CD spectroscopy. ¹H NMR analysis revealed a temperature-dependent cis–trans equilibrium in the hydroxamic acid architecture, influenced by neighboring units in the polymer chain. Additionally, the coordination ability of the hydroxamic acid moieties was investigated using a substitutionally inert palladium(II) complex. The formation of a bidentate coordination complex between the hydroxamic acid units and palladium(II) was confirmed by ¹H and ³¹P NMR spectroscopy. UV and CD spectra of the Pd-coordinated polymer showed new Cotton effects and absorptions, reflecting structural changes induced by metal coordination.