Rational Design of an Adenine-Based Coordination Polymer as a Dual Hydrogen-Bond Donor Heterogeneous Catalyst for Friedel–Crafts Alkylation and Cascade Deacetalization–Knoevenagel Condensation

Coordination polymers (CPs) have been widely studied as heterogeneous catalysts due to their Lewis-acid activity; however, the active site blockage from the strong metal-substrate interaction remains a challenge. As a promising alternative, hydrogen-bond-donating (HBD) catalysis, primarily driven by organic linkers, has been the area of recent interest. Thus, the judicious selection of linkers is crucial for synthesizing HBD-active CPs. In this context, biologically relevant adenine acts as an outstanding building block due to the presence of multiple binding sites. Herein, an adenine-based two-dimensional (2D) CP, SSICG-14 ([Zn (Ad)(HIPA)]·2H₂O), was synthesized by a solvothermal reaction between Zn salt, adenine (Ad), and a second-HBD functional group containing ligand 5-hydroxyisophthalic acid (HIPA). SSICG-14 shows high stability and contains two HBD functional groups, -NH₂ and -OH, which motivate us to utilize it as a heterogeneous catalyst for the Friedel-Crafts reaction and the cascade deacetalization-Knoevenagel condensation reaction. In both cases, SSICG-14 exhibited a high efficiency. Additionally, the importance of the strategic installation of two HBD-capable functional groups was established by comparing the efficiency of SSICG-14 with a previously reported Zn-CP without the presence of these HBD functional groups (-NH₂ and -OH). The significance of these HBD sites in the catalytic transformation was further established through fluorescence studies.