Iodide-Coordinated Single-Site Pd Catalysts for Alkyne Dialkoxycarbonylation

Heterogeneous single-metal-site catalysts (HSMSCs) have attracted considerable interest, but most studies have focused on the metal atoms in the active site while ignoring the key role of ligands. The unique coordination environment of a single-site catalyst is crucial for realizing its potential. Constructing this kind of catalyst via a feasible and practical fabrication method is challenging. Herein, a single-site Pd catalyst with iodide ligands supported on activated carbon (Pd-1/AC) was successfully fabricated by atomic dispersion of large Pd nanoparticles (NPs). Intermediate I center dot radicals were detected during the atomic dispersion process of Pd NPs by in situ imaging photoelectron photoion coincidence spectroscopy (in situ iPEPICO) with vacuum ultraviolet synchrotron radiation. The molecular structure of single-site Pd was established as [Pd(CO)I-4(O=AC)](2-) through combined characterization. Alkyne dialkoxycarbonylation with high selectivity toward 1,4-dicarboxylic acid esters (>94%) and high acetylene conversion (>99%) was achieved. A sulfonic promoter on the Pd-1/AC catalyst for alkyne dialkoxycarbonylation was avoided because of the iodide ligand. Good durability and a broad substrate scope were successfully achieved.

Automated summary

Heterogeneous single-metal-site catalysts have shown great potential, with this particular Pd catalyst achieving high selectivity towards 1,4-dicarboxylic acid esters (>94%) and high acetylene conversion (>99%) without the need for a sulfonic promoter. The catalyst, supported on activated carbon with iodide ligands, demonstrated good durability and a broad substrate scope.