Functionalized Pyridine-Based Iron(II) Complexes: Synthesis, Structural Characteristics and Catalytic Activity in...

Herein, we report four newly synthesized iron complexes 1, 2, 3, and 4 based on functionalized bipyridine, phenanthroline, and pyridine-imidazole ligands, along with their structural characterization and catalytic activity toward selective oxidation of alcohols to aldehydes. Structural analysis revealed that the oxidation state of iron is +2 in all the complexes with stabilization in the crystal lattice facilitated by diverse noncovalent interactions, including π-π stacking, C─H···π interactions, halogen···π interactions, and dipole-dipole interactions. Among the series, the electron-rich complex 1 demonstrated superior catalytic efficiency within short reaction times. Using NaIO₄ as a terminal oxidant, complex 1 enabled the conversion of a wide range of alcohols into the corresponding aldehydes in good to excellent yields, while being tolerant of common organic functional groups. The selective conversion of alcohols to aldehydes without overoxidation is highly essential in organic synthesis. The comparative catalytic performances of complexes 1-4 are rationalized by correlating their redox and structural properties. Based on several control experiments and literature reports, we have also proposed a plausible mechanism for present protocol.