Predesigned Metal-Anchored Building Block for In Situ Generation of Pd Nanoparticles in Porous Covalent Organic Framework: Application in Heterogeneous Tandem Catalysis

The development of nanoparticle–polymer-hybrid-based
heterogeneous
catalysts with high reactivity and good recyclability is highly desired
for their applications in the chemical and pharmaceutical industries.
Herein, we have developed a novel synthetic strategy by choosing a
predesigned metal-anchored building block for in situ generation of
metal (Pd) nanoparticles in the stable, porous, and crystalline covalent
organic framework (COF), without using conventional reducing agents.
In situ generation of Pd nanoparticles in the COF skeleton is explicitly
confirmed from PXRD, XPS, TEM images, and 15N NMR spectral
analysis. This hybrid material is found to be an excellent reusable
heterogeneous catalyst for the synthesis of biologically and pharmaceutically
important 2-substituted benzofurans from 2-bromophenols and terminal
alkynes via a tandem process with the turnover number up to 1101.
The heterogeneity of the catalytic process is unambiguously verified
by a mercury poisoning experiment and leaching test. This hybrid material
shows superior catalytic performance compared to commercially available
homogeneous as well as heterogeneous Pd catalysts.