Intramolecular Ligand Dynamics in d15-(PPh3)-Capped Gold Nanoparticles Investigated by 2H NMR

Abstract

The knowledge of intramolecular dynamics, geo-metric confinement, and structure of surface-bound ligands are important factors for understanding surface chemistry, catalysis, and design of catalytically optimized nanoparticles. In this report, intramolecular dynamics of perdeuterated triphenylphosphine ligands, d15-(PPh3), bound to the surface of gold nanoparticles (AuNPs) are characterized by pulsed deuteron nuclear magnetic resonance (2H NMR) in the solid state. The 2H quadrupolar echo Fourier transform NMR line shapes indicate fast 180° flip dynamics (π flip) of phenyl rings in surface-bound d15-(PPh3) ligands about the P−C bond at the rate of k ≥ 7 × 107 s−1. In contrast, the d15-(PPh3)AuCl complex, a model compound that is also present in this nanoparticle system, does not exhibit measurable π flips on the time scale sampled by the experiment (∼10−5 s). Its phenyl rings appear rigid from ambient temperature up to 386 K. The experimental 2H NMR line shape results are consistent with a theoretical mode...