Ultrasmall Palladium Nanoparticles Confined within Dendronized Polymers as High-Efficiency Catalysts

Palladium nanoparticles (PdNPs) have attracted considerable interest for years and have been extensively applied as nanocatalysts for hydrogenation and C–C cross-coupling reactions. In general, small PdNPs are highly active nanocatalysts. However, it is a challenge to prepare PdNP catalysts with a size of less than 1.0 nm. Here, ultrasmall PdNPs (ca. 1.0 nm) are prepared using the linear PG0 or dendronized PG1 and PG2 as stabilizers. The catalytic activity of G0-PdNPs (1.00 ± 0.4 nm), G1-PdNPs (0.99 ± 0.4 nm), and G2-PdNPs (0.98 ± 0.4 nm) is estimated and compared in the catalytic 4-nitrophenol reduction and Suzuki–Miyaura reactions. The G1-PdNPs are observed to show the highest catalytic activity for both the reactions. In the 4-nitrophenol reduction, G1-PdNPs had a rate constant of 4.25 × 10^–2 s^–1 and a turnover frequency of up to 18,750 h^–1. In the Suzuki–Miyaura reactions, G1-PdNPs with an ultralow dosage (50 ppm) can reach approximately quantitative yields with a turnover frequency of 3166 h^–1, and G1-PdNPs also exhibit good applicability and generality for different substrates. The current work provides a valuable reference for the design and preparation of ultrasmall PdNPs in catalysis.