Resolution of chiral nitrogen atoms in 1D helical coordination polymers

Abstract

A unique stereochemically labile secondary amine with a chiral nitrogen atom assemble cobalt and zinc ions in the aid of chelating ancillary ligands to give rise to three helical 1D coordination polymers, [Co(p‑cpdba)(2,2′‑bpy)]n (1), {[Zn(p‑cpdba)(2,2′‑bpy)]}n (2) and [Zn(p‑cpdba)(1,10‑phen)]n (3) (cpdba2− = 4‑(4‑carboxyphenylamino)‑3,5‑dinitrobenzolate, 2,2′‑bpy = 2,2′‑bipyridine, 1,10‑phen = 1,10‑phenanthroline). Compound 1 exhibits a racemic double-stranded chained structure with chelating 1,10‑phen occupying two sites of the octahedral cobalt(II). By changing to five-coordinated square pyramidal zinc(II) and employing 2,2′‑bpy and 1,10‑phen, two triple-stranded chained compounds 2 and 3 are synthesized. As expected, all chiral nitrogen atoms within each chiral chain of every triple-stranded helix in 2 and 3 have the same absolute configuration due to the confining growth along one dimension. Therefore, the resolution of chiral nitrogen atom is achieved though only at a one-dimensional scale.