Using an efficient photocatalyst Fe3O4@SiO2@(CH2)3N(CH2COOH)2-Cu (II) for photoinduced electron transfer (PET) reactions leading to tetrahydroquinoline derivatives

Abstract

Harnessing visible light for organic synthesis has garnered significant attention due to its efficiency and eco-friendly nature in producing valuable organic compounds. In this study, a magnetic nano-photocatalyst based on iminodiacetic acid (IDA) was designed and synthesized to facilitate the preparation of tetrahydroquinoline derivatives via a photoinduced electron transfer (PET) mechanism. IDA, serving as both a potent chelating agent and a visible light-sensitizing moiety, was immobilized onto the surface of silica-coated magnetic nanoparticles (Fe₃O₄@SiO₂). This immobilization was achieved using 3-aminopropyltriethoxysilane (APTES) as a coupling agent, which provides terminal amine groups to enhance light absorption. Subsequent complexation yielded the final nano-photocatalyst, designated as Fe₃O₄@SiO₂@(CH₂)₃N(CH₂COOH)₂-Cu (II). Different characterization techniques confirmed the successful synthesis and structural integrity of the nano-photocatalyst. Morphological analyses revealed that the nanoparticles retained their spherical shape post-functionalization. Under visible-light irradiation, the IDA-modified magnetic silica nanoparticles demonstrated exceptional catalytic activity, enabling the high-yield cyclization of tetrahydroquinoline derivatives with conjugated structures at ambient temperature in air. The IDA moiety plays a pivotal role by acting as a strong chelating ligand for transition metals such as copper, while the magnetic core facilitates easy separation and recovery for repeated use. The initial application of this nano-photocatalyst in tetrahydroquinoline synthesis, coupled with its robust reusability, underscores its significant catalytic efficiency. The resulting tetrahydroquinoline derivatives were thoroughly characterized using FT-IR, CHN elemental analysis, ¹H NMR, and ¹³C NMR spectroscopy.