Towards Responsive Spiroborate‐Based Assemblies of Podand‐Type Ligands Functionalized with Two Terminal/Peripheral Catecholate Moieties in the Presence of Alkali Cations

The synthesis of two ligands bearing two terminal catecholate binding sites connected by an oligo(ethyleneglycol) bridge of two distinct lengths and their self‐assembly upon boron coordination and alkali cation binding (M=Li, Na, K, Cs) are reported. Attempts to synthesize positional isomers of the ligands are also described. Binding of the four alkali cations M+ through M−O interactions was studied depending on the length of the oligo(ethyleneglycol) chain in solution by 1H and DOSY NMR, mass spectrometry (MS) and in the solid‐state by X‐ray diffraction (XRD) on single crystals. MS spectrometry as well as 1H NMR revealed the presence of monomeric and oligomeric spiroborate compounds. Two monomeric macrocycles could be characterized by XRD, entrapping either lithium or cesium cations within the spiroborate macrocycle. Flexible bis‐catecholate podand‐type ligands of various lengths were synthesized. Upon reaction with boric acid and a hydroxide alkaline solution, a spiroborate node forms and the alkali cation is wrapped by the flexible spacer. Influence of the spacer's length and the alkali cation size on the formation of monomeric or oligomeric spiroborate compounds was studied in solution by DOSY NMR.