Copper metallic nanoparticles capped with PEGylated PAMAM-G3 dendrimers for the catalytic reduction of low solubility nitroarenes of pharmaceutical interest

Copper nanoparticles (Cu NPs) were synthesized using NaBH₄ as reducing agent and increasing molar ratios of 50 % PEGylated polyamidoamine dendrimer of the third generation (PEG-PAMAM-G3) as a capping agent. The dendrimer-stabilized Cu NPs were evaluated as novel catalysts for the reduction of poorly soluble nitrocompounds in aqueous media. The nanocatalysts were characterized using transmission electron microscopy (TEM), ultraviolet-visible light (UV–vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and dynamic light scattering (DLS). UV–vis revealed the presence of localized surface resonance plasmon at 560 nm, whereas TEM analysis confirmed disperse and spherical Cu NPs of around 2.6–3.7 nm. The catalysts were successfully tested in the efficient aqueous reduction of 4-(4-nitrophenyl)morpholine as model low solubility substrate using NaBH₄ as reducing agent. The best catalytic performance was attained by the catalyst having a PAMAM:Cu ratio of 0.4, which retained its activity throughout four catalytic cycles. The catalyst was also efficient in the aqueous reduction of two pharmaceutically relevant building blocks such as 4-(2-fluoro-4-nitrophenyl)morpholine) and 4-(4-nitrophenyl)morpholin-3-one. Our results suggest that PEG-PAMAM-G3 prevents Cu NPs agglomeration and flocculation, and enhances their stability in aqueous solution thus enabling their use in environmentally friendly catalytic processes.