Using silyl protecting group to enable post-deposition C-C coupling reactions of alkyne-functionalized N-heterocyclic carbene monolayers on Au surfaces.

N-Heterocyclic carbenes (NHCs) were functionalized with a triisopropylsilyl (TIPS)-protected alkyne group and self-assembled on Au films to enable post-deposition functionalization by C-C coupling reactions. The TIPS group efficiently protected the alkyne and prevented its deprotonation during surface-anchoring of NHC. Sonogashira C-C coupling reactions were performed on the Au film in high yield following removal of the TIPS group, demonstrating that post-deposition coupling reactions can be employed to widen the chemical scope of surface-anchored NHCs.

Site-Independent Hydrogenation Reactions on Oxide-Supported Au Nanoparticles Facilitated by Intraparticle Hydrogen Atom Diffusion.

Metal-support interactions have been widely utilized for optimizing the catalytic reactivity of oxide-supported Au nanoparticles. Optimized reactivity was mainly detected with small (1-5 nm) oxide-supported Au nanoparticles and correlated to highly reactive sites at the oxide-metal interface. However, catalytically active sites are not necessarily restricted to the interface but reside as well on the Au surface. Uncovering the interconnection between reactive sites located at the interface and those situated at the metal surface is of crucial importance for understanding the reaction mechanism on Au nanoparticles. Herein, high-spatial-resolution IR nanospectroscopy measurements were conducted to map the localized reactivity in hydrogenation reactions on oxide-supported Au particles while using nitro-functionalized ligands as probes molecules. Comparative analysis of the reactivity pattern on single particles supported on various oxides revealed that oxide-dependent reactivity enhancement was not limited to the oxide-metal interface but was detected throughout the Au particle, leading to site-independent reactivity. These results indicate that reactive Au sites on both the oxide-metal interface and metal surface can activate the nitro groups toward hydrogenation reactions. The observed influence of oxide support (TiO2 > SiO2 > Al2O3) on the overall reactivity pattern specified that hydrogen dissociation occurred at the oxide-metal interface, followed by highly efficient intraparticle hydrogen atom diffusion to the interior parts of the Au particle. In contrast to Au particles, the oxide-metal interface had only a minor impact on the reactivity of supported Pt particles in which hydrogen dissociation and nitro group reduction were effectively activated on Pt sites. Single-particle measurements provided insights into the relative reactivity pattern of oxide-supported Au particles, revealing that the less-reactive Au metal sites can activate hydrogenation reactions in the presence of hydrogen atoms that diffuse from the Au/oxide boundary.