Nitrogen-rich dicyandiamide-grafted graphene oxide catalyst for the synthesis of 1,2,5,6-tetrahydropyridine-3-carboxylates

Abstract

In this study, a novel biomass-derived multifunctional catalyst, GO@APTES@DCDA@Sb³⁺, was successfully synthesized through sequential surface modification and thoroughly characterized by FT-IR spectroscopy, Raman spectroscopy, XRD analysis, ICP-MS analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The structural and morphological investigations confirmed the incorporation of nitrogen-rich groups and the uniform coordination of Sb³⁺ ions on the graphene oxide framework, which introduced multiple Lewis acidic sites. Catalytic performance was evaluated in the one-pot solvent-free synthesis of 1,2,5,6-tetrahydropyridine-3-carboxylate derivatives, where GO@APTES@DCDA@Sb³⁺ outperformed other metal-modified catalysts, affording up to 56% yield under optimized conditions (50 °C, 380 min, 5 mg catalyst). The anti-isomer was obtained with diastereomeric ratios (dr) up to 90 : 10–100 : 0. Kinetic assessments were conducted to confirm the catalyst's effectiveness in the newly developed reaction. Derived thermodynamic parameters showed ΔH^‡ = 0.9571 kJ mol⁻¹ and ΔS^‡ = −0.0144 kJ mol⁻¹ K⁻¹; notably, ΔG^‡ was found to increase progressively as a function of temperature. The catalyst showed excellent recyclability, maintaining high activity over repeated cycles, and demonstrated stability with negligible metal leaching. Furthermore, the methodology was successfully extended to gram-scale synthesis, highlighting its practical applicability.