An N-heterocyclic carbene ligand promotes highly selective alkyne semihydrogenation with copper nanoparticles supported on passivated silica

Abstract

Binding of an N-heterocyclic carbene to Cu nanoparticles on passivated silica enables high selectivity in alkyne semihydrogenation.

Direct Synthesis of N‐Heterocyclic Carbene‐Stabilized Copper Nanoparticles from an N‐Heterocyclic Carbene–Borane

“…In spite of numerous works concerning their syntheses and applications, Cu NPs are still challenging to prepare as a colloidal solution that is resistant to aggregation over time and with a metal surface that is neither oxidized nor hydroxylated as long as it is kept under inert atmosphere . Their stabilization with NHCs has only been reported recently, whereby NHCs were used as additional ligands on supported preformed nanoparticles to tune the catalytic activity for the hydrogenation of alkynes . Before this recent work, the interaction of copper surfaces with NHCs was mostly probed on self‐assembled monolayers on flat surfaces, and also on supported Cu NPs post‐grafted with IMes NHC [1,3‐bis(2,4,6‐trimethylphenyl)‐1,3‐dihydro‐2 H ‐imidazol‐2‐ylidene] .…”

Small and Narrowly Distributed Copper Nanoparticles Supported on Carbon Prepared by Surface Organometallic Chemistry for Selective Hydrogenation and CO2 Electroconversion Processes

“…We then investigated the use of Cu/C B in alkyne hydrogenation since the corresponding silica‐supported Cu nanoparticles via SOMC showed good catalytic performances towards the semihydrogenation of alkynes . 1‐Phenyl‐1‐propyne was used as a prototypical substrate ( S , Table a) with Cu/C B (0.8 Cu mol %).…”

“…On the other hand, introducing 2 % mol of tricyclohexylphosphine (PCy 3 ) in the catalytic mixture allows reaching a selectivity of 84 % towards ( Z )− S 2H at full conversion of S (entry 4, Table b). The selectivity towards ( Z )− S 2H was further increased to 91 % selectivity upon using the more efficient N‐heterocyclic ligand IMes in place of PCy 3 , (entry 5, Table b) . The increased selectivity obtained with IMes originates from the competitive binding of this ligand on Cu NPs, which enables the adsorption of S and its conversion to S 2H , but adsorbs preferentially than the generated S 2H , hindering overhydrogenation .…”

“…The thus‐obtained nanoparticles have typically small size (1–10 nm range) that depends mainly on the metal and less on the support itself. For instance, this approach has been successfully applied to generate 2–5 nm particles of coinage metals as Cu– but also Ag or Au on silica, alumina, zirconia, titania as well as tailored supports. In the specific case of Cu, we have shown that highly dispersed nanoparticles supported on silica ( Cu/SiO 2 ) efficiently catalyze the semihydrogenation of alkynes in the presence of organic ligands, with performance reaching that of noble metal catalysts such as Lindlar Pd.…”

“…For instance, this approach has been successfully applied to generate 2–5 nm particles of coinage metals as Cu– but also Ag or Au on silica, alumina, zirconia, titania as well as tailored supports. In the specific case of Cu, we have shown that highly dispersed nanoparticles supported on silica ( Cu/SiO 2 ) efficiently catalyze the semihydrogenation of alkynes in the presence of organic ligands, with performance reaching that of noble metal catalysts such as Lindlar Pd. We also discovered that Cu/SiO 2 can selectively catalyze the hydrogenation of the olefinic bond of α,β‐conjugated esters, whereas commercial Cu/ZnO/Al 2 O 3 or large Cu nanoparticles are inactive for that transformation, underlining the single behaviour of small and dispersed nanoparticles …”