Amino-ether macrocycle that forms Cu^II templated threaded heteroleptic complexes: a detailed selectivity, structural and theoretical investigations

Abstract

A new oxy(ether)tris(amine) macrocycle, MC has been synthesized for Cu^II complex formation within the cavity of the macrocyclic wheel in endotopic fashion. This complex is further reacted with the bidentate chelating ligands, 1,10-phenanthroline (L1), 2,2′-bipyridyl (L2), 4,4′-dimethyl-2,2′-bipyridyl (L3) and 5,5′-dimethyl-2,2′-bipyridyl (L4) to achieve the pseudorotaxanes PRT1–PRT4, respectively. These bis-heteroleptic complexes were characterized by the electrospray ionization mass spectrometry (ESI-MS), UV/Vis, EPR spectroscopy and Single-crystal X-ray structural analysis. Binding constants of the heteroleptic complexes were found in the range of 1.16 × 10² to 1.55 × 10³ M⁻¹ in acetonitrile. Further, the double level selectivity studies of MC using different metal ions [Co^II, Ni^II, Cu^II, Zn^II] and a number of simple bidentate chelating ligands shows the selective formation of PRT1 that justifies the self-sorting nature of the system. Further, substitution of axles from pseudorotaxanes PRT2–PRT4 could also be achieved by L1 with nearly 100% efficiency. To corroborate the experimental studies (comparison with the crystal geometry, importance of the π–π stacking, etc.) the geometries of the pseudorotaxanes were optimized using DFT (B3LYP) in the gas phase.