Synthesis and characterization of In(iii) S-thiobenzoylthioglycolate complexes and their catalytic applications in CO2 fixation and multicomponent synthetic reactions†

Indium(III) complexes of S-thiobenzoylthioglycolate (Stbtg) with nitrogen-donor ligands, such as 2,2′-bipyridyl and 1,10-phenanthroline, have been synthesized. The complexes [In(1,10-phen)(Stbtg)₃] (1), [In(2,2′-bipy)(Stbtg)₃] (2), and a thioglycolate salt, Na[In(2,2′-bipy)(SCH₂COO)₂]·H₂O (3), obtained by the decomposition of thiobenzoylthioglycolate complexes, were fully characterized using NMR and IR spectroscopy and single-crystal X-ray diffraction. The catalytic activities of these complexes were evaluated for two significant types of reactions. Complex 1 demonstrated exceptional catalytic efficiency in the Knoevenagel condensation and Knoevenagel-initiated multicomponent reactions (MCRs) for the synthesis of 2-amino-4H-chromene derivatives, including cyclohexane-1,3-dione, 5,5-dimethylcyclohexane-1,3-dione, 4-hydroxycoumarin, barbituric acid, and 2-aminobenzimidazole. Additionally, the complexes were found to be highly effective in CO₂ fixation reactions, with complex 1 exhibiting the highest activity, followed by 2 and 3. These results highlight the potential of In(III) complexes as catalysts in a variety of applications, such as organic synthesis and environmentally significant CO₂ fixation, demonstrating the broad applicability of non-transition metal complexes in sustainable chemical processes.