Enantiopure Chiral Coordination Polymers Based on Polynuclear Paddlewheel Helices and Arsenyl Tartrate

Abstract

Herein, we report the preparation of chiral, one-dimensional coordination polymers based on trinuclear paddlewheel helices [M3(dpa)4]2+ (M = Co(II) and Ni(II); dpa = the anion of 2,2′-dipyridylamine). Enantiomeric resolution of a racemic mixture of [M3(dpa)4]2+ complexes was achieved by chiral recognition of the respective enantiomer by [Δ-As2(tartrate)2]2− or [Λ-As2(tartrate)2]2− in N,N-dimethylformamide (DMF), affording crystalline coordination polymers formed from [(Δ-Co3(dpa)4)(Λ-As2(tartrate)2)]·3DMF (Δ-1), [(Λ-Co3(dpa)4)(Δ-As2(tartrate)2)]·3DMF (Λ-1), [(Δ-Ni3(dpa)4)(Λ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Δ-2) or [(Λ-Ni3(dpa)4)(Δ-As2(tartrate)2)]·(4 − n)DMF∙nEt2O (Λ-2) repeating units. UV-visible circular dichroism spectra of the complexes in DMF solutions demonstrate the efficient isolation of optically active species. The helicoidal [M3(dpa)4]2+ units that were obtained display high stability towards racemization as shown by the absence of an evolution of the dichroic signals after several days at room temperature and only a small decrease of the signal after 3 h at 80 °C.