Metal Complexes of Indigo and of Some Related Ligands

Abstract

While the first coordination compounds of indigo were reported over 100 years ago, a systematic study of the coordination chemistry of this important dye and also its structural “relatives” remained silent for over half a century. Only in the last two decades of the 20th century research on this topic started again keeps on growing ever since. It could be established, mainly by X‐ray crystallography, but also by many other modern spectroscopic techniques, that deprotonated indigo, and its deprotonated oxidized and reduced forms act as mono‐ and bidentate chelate ligands in metal complexes

The Indigo Isomer Epindolidione as a Redox‐Active Bridging Ligand for Diruthenium Complexes

“…It is thus likely that the two facile reduction processesR 1a nd R2 for [2](ClO 4 ) 2 are attributable to electron uptake by pap ligandso n opposite sides of the dinuclearm olecule. On the other hand, the crowding of reductions R1-R5 at negative potentials for [1](ClO 4 ) 2 suggests bpy-based processes with little intramolecular interaction. The number of electrons associated with the reversible redox processes in Figure2 was evaluated by spectroelectrochemistry (see below).…”

“…The complexes were purified by columnc hromatography (see the Experimental Section). Thin layer chromatographic (TLC) experimentsf urther establishedt he exclusivef ormationo fo ne diastereomeric form for both [1](ClO 4 ) 2 and [2](ClO 4 ) 2 ,identified as the meso isomer in both cases (see below).…”

“…The molecular structureso ft he dications in the crystals of [1](ClO 4 ) 2 and[ 2](ClO 4 ) 2 were determined by X-ray crystallography ( Figure 1, Ta ble 1). The bpy-containing compound crystallizes with two independent molecules ( Figure S4 in the Supporting Information).…”

“…The halfwave potential E 1/2 was set equal to 0.5(E pa + E pc ), where E pa and E pc are anodic and cathodic cyclic voltammetry peak potentials, respectively. 1 HNMR spectra were recorded with aB ruker AvanceI II in EtOH (40 mL) was heated to reflux for 2h and the precipitated AgCl was filtered off through as intered Gooch crucible. The filtrate was added to ap reheated ethanolic solution (20 mL) of the ligand (H 2 L, 25 mg, 0.095 mmol) and Et 3 N( 20 mg, 0.20 mmol) and heated at reflux under dinitrogen atmosphere for 8h.T he solvent was removed under reduced pressure and the residue was moistened with af ew drops of CH 3 CN and as aturated aqueous solution of NaClO 4 was added.…”

“…Single crystals of [1](ClO 4 ) 2 and [2](ClO 4 ) 2 were grown by slow evaporation of their 1:1C H 2 Cl 2 /CH 3 OH solutions. X-ray diffraction data were collected by using aR igaku Saturn-724 + CCD singlecrystal diffractometer using Mo Ka radiation at 150(2) K. The data collection was evaluated by using the CrystalClear-SM Expert software.…”