Thiazolo[5,4-d]thiazole-Based Metal-Organic Framework for Catalytic CO₂ Cycloaddition and Photocatalytic Benzylamine...

Metal-organic frameworks (MOFs) with permanent porosity and multifunctional catalytic sites constructed by two or more organic ligands are regarded as effective heterogeneous catalysts to improve certain organic catalytic reactions. In this work, a pillared-layer Zn-MOF (MOF-LS10) was constructed by 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine (H₄TCPP) and 2,5-di(pyridin-4-yl)thiazolo[5,4-d]thiazole (DPTZTZ). After activation, MOF-LS10 has a permanent porosity and moderate CO₂ adsorption capacity. The introduction of thiazolo[5,4-d]thiazole (TZTZ), a photoactive unit, into the framework endows MOF-LS10 with excellent photocatalytic performance. MOF-LS10 can not only efficiently catalyze the formation of cyclic carbonates from CO₂ and epoxide substrates under mild conditions but also can photocatalyze benzylamine coupling at room temperature. In addition, we used another two ligands 1,2,4,5-tetrakis(4-carboxyphenyl)benzene (H₄BTEB) and 1,4-di(pyridin-4-yl)benzene (DPB) to synthesize MOF-LS11 (constructed by BTEB^4- and DPTZTZ) and MOF-LS12 (constructed by TCPP^4- and DPB) in order to explore whether the pyrazine structural unit and the TZTZ structural unit synergistically catalyze the reaction. The electron paramagnetic resonance spectrum demonstrates that the superoxide radical (^·O₂^-), generated by electron transfer from the MOF excited by light to the oxidant, is the main active substance of oxidation. The design and synthesis of MOF-LS10 provide an effective synthetic strategy for the development of versatile heterogeneous catalysts for various organic reactions and a wide range of substrates.