Hg(II) Complexes Constructed from Indazole Ligands as New Heterogeneous Catalyst for the Biginelli/Transesterification Reaction: Synthesis and Quantum-Chemical Investigations

The present work deals with the synthesis, spectral characterization, DFT calculations, and catalytic activity of the new Hg(II) complexes derived from indazole ligands. The o-amino-ketones were obtained from the reduction of 6H-isoxazolo[4,3-e]indazoles as new heterocyclic ligands. Coordination of the ligands to Hg(II) cation led to the formation of new Hg(II) complexes. The IR, mass, and NMR spectra as well as the elemental analyses confirmed the structures of the new complexes. Furthermore, the DFT calculations at the B3LYP/6-311+G(d,p) level were used to gain further insight into the geometry of Hg(II) complexes. The catalytic activity of Hg(II) complexes as heterogeneous catalysts was studied for the synthesis of biologically active 3,4-dihydropyrimidin-2(1H)-one C5 ester (DHPMs), using classical Biginelli reaction followed by transesterification transformation. The results showed that the presented method gave the products good to excellent yields at reduced reaction time, which might be owing to the increased reactivity of the reactants on the surface area of Hg(II) complexes.