Oligosaccharide binding to a boronic-acid-appended phenanthroline·Cu(I) complex which creates superstructural helicates and catenates

Compound 2 bearing two boronic acid moieties at two sides of a 1,10-phenanthroline moiety was synthesized. 2 forms a 1:2 complex with Cu(I) and four boronic acid groups are arranged in the peripheral positions around the central metal chelate. When a saccharide guest links two boronic acid groups in the different ligands, the resultant structure is classified into a helicate, whereas when a saccharide guest links two boronic acid groups in the same ligands, the resultant structure is classified into a catenate. Careful examination of the CD spectra of 2₂·Cu(I) complex with saccharides established that (i) the D-glucose complex gives the helicate with P-helicity, (ii) the maltose complex give the helicate with M-helicity, (iii) the maltopentaose and maltohexaose complexes give the catenate with P-helicity, and (iv) maltotriose and maltotetraose cannot provide the stable complex with 2₂·Cu(I). The results indicate that 2₂·Cu(I) can act as a versatile core to create various superstructures using a boronic acid-saccharide interaction.