Trinuclear cis-dioxidomolybdenum(VI) complexes of compartmental C3 symmetric ligands: Synthesis, characterization, DFT study and catalytic application for hydropyridines (Hps) via the Hantzsch reaction

Abstract

Trinuclear cis-dioxidomolybdenum(VI) complexes of the type [{MoVIO2(MeOH)}3L1-7] (1–7) have been synthesized using tris(H2ONO) donor ligands [H6L1-7 (I–VII)] assembled from benzene-1,3,5-tricarbohydrazide (bthz) and the corresponding salicylaldehyde (sal). All the ligands and the complexes were characterized by numerous techniques, such as FT-IR, UV–visible, NMR (1H and 13C) spectroscopy, electrochemical study, elemental analysis, thermogravimetric study and single crystal X-ray diffraction of the ligand III and complexes 1 and 5. In the presence of H2O2 as an oxidant, these complexes show excellent catalytic potential towards the one-pot three-components [ethyl acetoacetate, benzaldehyde (or its derivatives) and ammonium acetate] dynamic covalent assembly in the Hantzsch reaction. Under solvent free conditions, as high as 98% conversion along with 100% selectivity towards diethyl 2,6-dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicarboxylate (1,4-DHP) has been achieved in 1 h. Although solvents do not improve the conversion, they do influence the selectivity of the products. With the elapse of time, the conversion of dihydropyridine to the diethyl 2,6-dimethyl-4-phenylpyridine-3,5-dicarboxylate derivative occurs and completes in ca. 10 h with a distinct color change, showing the importance of the catalysts. Efforts have been made to provide suitable reaction pathways for the catalytic reaction based on spectroscopic and density functional theory studies.