Coordination preferences of 3,3′-biisoxazolidines: A new kind of conformationally flexible chelating ligand

Abstract

3,3′-Bi{2-methyl-5-Ar}isoxazolidines (Ar = 2-Py, L 1; Ph, L 2) were designed as new conformational flexible N-donor multidentates. They readily form complexes with metal ions and the coordination preferences of the ligands were characterized by means of 1H NMR spectroscopy and X-ray crystallography. In the [(Cp*IrCl 2) 2{L 1}] complex the ligand bridges two iridium ions employing pyridyl-N functions, while in [Cp*Ir(L 2)Cl]Cl and Cu{L 2}Cl 2 · CHCl 3 the ligand forms five-membered chelates via the isoxazolidine nitrogen atoms. Tridentate coordination in [Ni{L 1}(H 2O)(NO 3)]NO 3 supports formation of two chelates involving donors of two isoxazolidine and of pyridyl groups, with a facial arrangement of the binding sites around octahedral Ni ions. In associate [UO 2(CH 3OH) 2(NO 3) 2] · L 1 the non-coordinating biisoxazolidine is involved in hydrogen bonding with molecular bis-methanol uranyl nitrate moieties.