Oxidative Elimination and Reductive Addition of Thiol‐Terminated Polymer Ligands to Metal Nanoparticles

Abstract

Metal nanoparticles (NPs) stabilized with thiol-(HS-) terminated polymers have applications in medicine, optoelectronics, and catalysis. It is assumed that upon exposure to oxidants or even air, these NPs lose colloidal stability, due to the oxidation of the HSend-group and elimination of polymer ligands from the NP surface, however, this mechanism does not explain the unsuccessful recovery of the NP stability by adding fresh HS-terminated polymers. Here we propose the oxidation of the surface metal atoms as a mechanism for the oxidative elimination of polymer from the NP surface. Based on this mechanism, we reversed NP aggregation by reducing the oxidized metal surface and re-attaching HS-terminated polymer ligands. This mechanism is general for various metal NPs and different HSterminated polymers. We show that oxidative elimination and reductive addition reactions can improve the colloidal stability of polymer-capped metal NPs and control their redox stimuli-responsive self-assembly.

Visualizing Formation of High Entropy Alloy Nanoparticles by Aggregation of Amorphous Metal Cluster Intermediates

“…Prior work in our lab showed that excessive aggregation of alloyed nanoparticles as seen here was likely due to large concentrations of hydroxyl radicals in solution, which can cause ligand desorption or intermolecular crosslinking of surface ligands. 43,66 These in situ results were qualitatively consistent with NaBH4 reduction experiments that showed particle aggregation for metal to ligand ratios of > 5:1, although aggregation was more severe during the LPTEM experiments with a lower metal:ligand ratio due to the presence of oxidizing hydroxyl radicals.…”

“…46 Similarly, we utilized lower metal:ligand ratios than solution chemical synthesis because our previous work demonstrated that excess ligand was required to scavenge oxidizing hydroxyl radicals that can preferentially oxidize some metals and desorb ligands via oxidative elimination. 43,65,66 (diffusion limited) to 𝑑~𝑡 1/2 (reaction limited). 67 Prior in situ small angle x-ray scattering (SAXS) revealed similar linear increases in particle diameter with time during aggregative growth of gold nanoparticles by NaBH4 reduction of aqueous gold chloride.…”