Using fewer catalysts to promote the chemical conversion of more substrates is the dream synthesis pursued by synthetic chemists. Achieving highly selective reactions using trace amounts (< 1 ppm) of catalysts is rare and has undoubted practical value. Herein, we designed and synthesized a single-atom Pd-metalated porous organic ligand polymer, denoted as Pd₁@POL, and used the polymer to realize the regioselective hydrosilylation of allenes (Pd loading was as low as 0.98 ppm). The synergistic effect of the dispersed catalytic active sites in the catalyst and supports with ligand regulation function can directionally realize the formation of specifically configured hydrosilylation products. The as-fabricated single-atom catalyst (SAC; i.e., Pd₁@POL-5) showed an amazing catalytic efficiency and selectivity for hydrosilylation of allene (turnover number was up to 772,358, which was 200 times higher than previously recorded, and regioselectivity > 100:1). The catalyst could be recycled numerous times in a continuous flow system without reductions in activity and selectivity. This work demonstrated the application prospect of the SAC in the synthesis of complex organic compounds and trace amount catalysis, which can lay the foundation for its large-scale and industrialized application in drug synthesis and other fields.

Single-atom site (SAS) catalysts have attracted considerable attention due to their excellent performance. However, most of the current research models of SAS catalysts are based on inorganic catalysts, where "metal and coordination atom interaction" cannot simulate the fine-tuning effect of organic ligands on metal catalytic centers in homogeneous catalysts. Therefore, certain chemical transformations in homogeneous catalysis cannot be perfectly replicated. Here, we used porous organic ligand polymers as the carrier, which effectively changes the charge regulation of nanoparticles and monoatomic metal catalysts. Drawing lessons from traditional homogeneous metal/ligand catalysis, we introduced various functional groups into the ligand polymers to adjust the electronic properties, and successfully realized the hydrosilylation of internal alkynes with high catalytic performance. The selectivity and catalytic efficiency under the Pd@POL-1 catalyst system were improved compared with previous studies. The internal alkynes with various structures can complete this reaction, and the ratio of E/Z can reach up to 100:1.