Silica-Supported Cu Nanoparticle Catalysts for Alkyne Semihydrogenation: Effect of Ligands on Rates and Selectivity

Abstract

Narrowly dispersed, silica-supported Cu nanoparticles (ca. 2 nm) prepared via surface organometallic chemistry from a mesityl complex [CuMes] are highly active for the hydrogenation of a broad range of alkynes. High-throughput experimentation allows for identifying the optimal ligand and reaction conditions to turn these supported Cu nanoparticles into highly chemo- and stereoselective catalysts for the preparation of Z-olefins (overall, 23 examples). For instance, PCy-modified Cu nanoparticles semihydrogenate 1-phenyl-1-propyne to cis-β-methylstyrene (20 bar H, 40 °C) with turnover number and turnover frequency of ca. 540 and 1.9 min, respectively, and with 94% selectivity at full conversion.

Pairwise hydrogen addition in the selective semihydrogenation of alkynes on silica-supported Cu catalysts

“…9 This synthetic protocol provided silica-supported Cu(0) nanoparticles with an average size in the range 1.9 ± 0.3 nm, as determined by high-angle annular dark field scanning transmission microscopy after the sample was slowly exposed to air. 9 Treatment of Cu/SiO 2-700 with PCy 3 afforded a surface-modified catalyst (Cy 3 P–Cu/SiO 2-700 ) with enhanced selectivity in alkyne batch semihydrogenation. 9 Both catalysts were then used in the PHIP experiments with 1-butyne, 1-butene or 2-butyne.…”

“…9 Treatment of Cu/SiO 2-700 with PCy 3 afforded a surface-modified catalyst (Cy 3 P–Cu/SiO 2-700 ) with enhanced selectivity in alkyne batch semihydrogenation. 9 Both catalysts were then used in the PHIP experiments with 1-butyne, 1-butene or 2-butyne.…”

“…Subsequent impregnation of this material with tricyclohexylphosphine yields the Cy 3 P–Cu/SiO 2-700 catalyst, as reported in detail elsewhere. 9 …”

“…It has been recently demonstrated by some of us that combining small silica-supported Cu nanoparticles and a phosphorus-based ligand allows one to achieve this goal. 9 However, a more detailed understanding of the reaction mechanism and the role of the phosphine ligand is critically needed to aid the rational development of improved catalysts.…”

Reduction of phenylacetylenes using Raney Ni–Al alloy, Al powder in the presence of noble metal catalysts in water

“…6,7 Recently, use of a copper catalyst as a monophasic catalytic system and silica-supported copper nanoparticles have been employed for the selective semireduction of alkynes. 8,9 In another study, a nonclasical…”