A comparative study for the efficiency of Pd (II) and Fe (III) complexes as efficient catalysts for synthesis of dihydro-7H-5-thia-hexaaza-s-indacen-6-one derivatives supported with DFT approach

Two novel complexes were synthesized by the reaction of benzothiazol-pyrimidin-2-ylidene ligand (BTP) with Pd (II) and Fe (III) ions. A variety of various spectral and analytical methods (infrared, ¹H/NMR, ¹³C/NMR, electronic spectra, CHN analyses, mass spectra, thermogravimetric analysis, and magnetic susceptibility) were used to characterize the investigated BTP ligand and its complexes. Correlation of experimental results with density functional theory calculation proves that the geometry of BTP-Fe complex is octahedral, whereas BTP-Pd complex is square planner. The catalytic effectiveness of BTP complexes were tested for three-component condensation process under moderate and environmentally friendly reaction conditions. Moreover, the effects of different Lewis acid, basic, and ionic liquid catalysts, as well as solvent and catalyst dose on the catalytic reaction were investigated. Both catalysts demonstrated strong catalytic capability in the carefully regulated ideal reaction circumstances. Heterogeneous catalyst BTP-Pd exhibited superior catalytic performance compared to homogeneous catalyst BTP-Fe. All products were obtained in high TOF (turnover frequency) numbers in the presence of these catalysts, which indicate the high efficiency of these catalysts in the synthesis of dihydro-7H-5-thia-hexaaza-s-indacen-6-one derivatives. Moreover, the two catalysts' recycling and reusability in reactions were also investigated. Heterogeneous BTP-Pd catalyst could be reused up to seven times with high efficiency, but the homogeneous catalyst (BTP-Fe) could only be recycled up to four times. Furthermore, the mechanism of catalytic reaction was suggested and supported by DFT calculation. The simplicity, safety, stability, use of commercially available catalysts, quick reaction times, and excellent yields make it promising for future industrial use.