Ullmann‐Type <i>N</i> ‐Heteroarylation of Nitrogen Heterocycles Catalyzed by Heterogeneous CuNPs/HKUST‐1

ABSTRACT Ullmann‐type C–N coupling is an essential reaction to construct functional nitrogen heterocycles, whereas conventional copper catalytic systems are hampered by poor recoverability and residual metal contamination, hindering their green application. In this work, a Cu nanoparticle‐immobilized HKUST‐1 (CuNPs/HKUST‐1) composite was prepared at room temperature via a simple green strategy, using cheap commercial copper powder as the sole copper source. The as‐prepared CuNPs/HKUST‐1 displayed high catalytic activity for the Ullmann N ‐arylation of diverse nitrogen heterocycles with aryl iodides under an air atmosphere, delivering 88% isolated yield for the model reaction under optimized conditions. Notably, the method exhibited broad substrate scope, tolerating steric hindrance and diverse electronic substituents to achieve a maximum isolated yield of 99%. Owing to the strong interaction between copper nanoparticles and HKUST‐1 framework, the catalyst maintained favorable catalytic performance after 10 runs, with an ultralow copper leaching amount of 0.3%. Furthermore, Cu 2p and Cu LMM Auger spectra verified that surface Cu(0) and Cu(I) species served as the main active sites, and a possible catalytic mechanism based on low‐valent copper active sites was proposed. This work develops a facile and low‐cost strategy for fabricating recyclable copper‐based MOF catalysts, which shows great promise for environmentally friendly synthesis of nitrogen‐containing fine chemicals.