The heptazine-based microporous polymer HMP-TAPA was synthesized via a direct nucleophilic substitution reaction between trichloroheptazine and tris(4-aminophenyl)amine (TAPA), resulting in a highly porous, stable, and multifunctional organic framework. The material exhibits a surface area of 424 m²/g—the highest reported for any heptazine-based polymeric network—due to the use of a small, electron-rich trigonal linker, TAPA, which enhances both porosity and electronic functionality. This structural design enables efficient visible-light absorption across a broad spectral range, with a band gap of 2.32 eV derived from Tauc plot analysis of UV/Vis diffuse reflectance data. The conduction band edge is positioned at −0.53 V vs. NHE, while the valence band lies at +1.79 V vs. NHE, creating favorable energetics for photoinduced charge separation and oxygen reduction.
HMP-TAPA functions as an effective metal-free photocatalyst for the oxidative homocoupling of benzylamine to dibenzylimine under visible light irradiation. In optimized conditions, 94% conversion of benzylamine was achieved with exceptional selectivity (98%) toward the desired imine product. Control experiments confirmed that neither light nor catalyst alone initiated the reaction, underscoring the necessity of both components. The mechanism involves photogenerated holes oxidizing benzylamine to its radical cation, which increases the acidity of the benzylic C–H bond. Simultaneously, electrons reduce molecular oxygen to superoxide radicals, which abstract hydrogen from the radical cation to form a benzyliminium ion. Subsequent dehydration and coupling yield dibenzylimine. The critical role of superoxide radicals was verified by quenching experiments using TEMPO, which reduced conversion to only 11%.69-53-4 supplier EPR spectroscopy further confirmed the presence of superoxide species during irradiation.
Notably, HMP-TAPA also demonstrates strong heterogeneous base catalytic activity, attributed to its high nitrogen content and abundant surface basic sites. Temperature-programmed desorption of CO₂ revealed two distinct desorption peaks at 92 °C and 352 °C, corresponding to weak and strong basic sites, respectively. The total concentration of basic sites was quantified at 278 mol/g—significantly higher than g-C₃N₄ (44 mol/g)—indicating superior potential for base-catalyzed reactions. This property enabled efficient Knoevenagel condensation between aromatic aldehydes and active methylene compounds such as methyl cyanoacetate and malononitrile under mild, base-free conditions at room temperature. Reactions proceeded rapidly, achieving >99% conversion within 3 hours for electron-withdrawing aldehydes (e.g., p-chloro-, p-nitrobenzaldehyde), while electron-donating groups (e.g., p-anisaldehyde) showed slower kinetics due to reduced electrophilicity of the carbonyl carbon. The mechanism proceeds via deprotonation of the active methylene compound at surface N–H sites, followed by nucleophilic attack on the carbonyl group, forming an oxyanion intermediate that undergoes dehydration to yield α,β-unsaturated esters.BSA Antibody MedChemExpress
The catalyst exhibited excellent recyclability, maintaining high activity over five consecutive cycles without significant loss in performance.PMID:34695364 Post-recycling characterization by SEM, FTIR, and UV/Vis spectroscopy confirmed retention of morphology, chemical structure, and optical properties. Furthermore, HMP-TAPA displayed remarkable chemical stability across extreme pH conditions, remaining intact after prolonged exposure to concentrated H₂SO₄ (18 N), HCl (12 N), and NaOH (6–9 N). This resilience stems from extensive intramolecular hydrogen bonding within the heptazine framework, which shields C–N bonds from hydrolysis through steric hindrance and hydrophobic microenvironments.
In summary, HMP-TAPA emerges as a versatile, robust, and highly functional heterogeneous catalyst capable of enabling dual-mode reactivity: photocatalytic oxidation and base-catalyzed C–C bond formation. Its high surface area, tunable electronic structure, and exceptional stability make it uniquely suited for sustainable chemical transformations under ambient conditions. This work highlights the power of rational design in constructing advanced porous polymers with tailored functionalities for diverse applications in green chemistry and materials science.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
