Synthesis of Homoleptic and Heteroleptic Ruthenium Complexes Appended with Glucosyl Ligand by the Click-to-Chelate Approach

Abstract

Homoleptic and heteroleptic complexes of Ru(TAGP-tapy)₃Cl₂ {TAGP-tapy is 2-[1-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-1H-1,2,3-triazol-4-yl]-pyridine} bearing a clustered glucose-derived ligand and Ru(bpy)₂(TAGP-tapy)Cl₂ (bpy is 2,2'-bipyridine) have been synthesized by the chelating reaction of RuCl₃·3H₂O with TAGP-tapy and cis-Ru(bpy)₂Cl₂ with TAGP-tapy, respectively. The bidentate 1,2,3-triazolelinked glucose-derived ligand TAGP-tapy was prepared by copper-catalyzed coupling (click reaction) of 2-ethynylpyridine with acetyl protected glucosyl azide, 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl azide (TAGP-N₃). TAGP-N₃ was prepared by nucleophilic substitution reaction of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (TAGP-Br) with NaN₃. These ruthenium complexes were purified by column chromatography or HPLC. Structures of the intermediates and ruthenium complexes were confirmed by HPLC, ¹H and ¹³C NMR, FT-IR, and ESI-MS spectroscopies. UV-Vis and fluorescence spectroscopic methods were used to study optical properties of the ligand TAGP-tapy and ruthenium complexes. TAGP-tapy exhibited interesting solvent-polarity dependent fluorescence properties and a significant red-shift in emissions. Both complexes demonstrated distinctive fluorescence emission band in the visible region.