Organometallic Nanoparticles Ligated by NHCs: Synthesis, Surface Chemistry and Ligand Effects

Abstract

Over the last 20 years, the use of metallic nanoparticles (MNPs) in catalysis has awakened a great interest in the scientific community, mainly due to the many advantages of this kind of nanostructures in catalytic applications. MNPs exhibit the characteristic stability of heterogeneous catalysts, but with a higher active surface area than conventional metallic materials. However, despite their higher activity, MNPs present a wide variety of active sites, which makes it difficult to control their selectivity in catalytic processes. An efficient way to modulate the activity/selectivity of MNPs is the use of coordinating ligands, which transforms the MNP surface, subsequently modifying the nanoparticle catalytic properties. In relation to this, the use of Nheterocyclic carbenes (NHC) as stabilizing ligands has been demonstrated to be an effective tool to modify the size, stability, solubility and catalytic reactivity of MNPs. Although NHC-stabilized MNPs can be prepared by different synthetic methods, this review is centered on those prepared by an organometallic approach. Here, an organometallic precursor is decomposed under H2 in the presence of non-stoichiometric amounts of the corresponding NHC-ligand. The resulting organometallic nanoparticles present a clean surface, which makes them perfect candidates for catalytic applications and surface studies. In short, this revision study emphasizes the great versatility of NHC ligands as MNP stabilizers, as well as their influence on catalysis.

N-heterocyclic carbene adsorption states on Pt(111) and Ru(0001)

“…[37][38][39][40] In contrast to the growing body of work on Pt, published studies of NHC-ligands on Ru are limited to nanoparticles prepared for use in heterogeneous catalysis reactions. 3,14,44 The present understanding of NHCs on coinage metal surfaces was gained from combined data obtained by several research groups using a wide range of surface science techniques, in addition to data from computational studies. Although RAIRS (reflectance-absorbance infrared spectroscopy) is a particularly informative surface analysis technique, to date it was only used in a small number of studies of NHCs on extended surfaces.…”

Functionalization of Metal-Supported Graphene by an N-Heterocyclic Carbene

“…N-heterocyclic carbene ligands (NHCs) are increasingly used to modify the properties of nanoparticles and extended surfaces of inorganic materials. − These persistent carbenes form chemically and thermally robust and addressable adsorption layers on metals − and they can be used to tune catalytic ,, and electronic , properties. Rapid developments in the field are facilitated by the increasing availability of easily handled precursor salts that do not co-deposit strongly adsorbing counterions. , The great majority of the work on surfaces deals with the modification of coinage metals. − Considerably less attention has been given to Pt-group metals − and, to our knowledge, only Yoon et al described the grafting of an NHC to graphene.…”

“…N-heterocyclic carbene ligands (NHCs) are increasingly used to modify the properties of nanoparticles and extended surfaces of inorganic materials. 1−6 These persistent carbenes form chemically and thermally robust and addressable adsorption layers on metals 7−11 and they can be used to tune catalytic 3,12,13 and electronic 14,15 properties. Rapid developments in the field are facilitated by the increasing availability of easily handled precursor salts that do not codeposit strongly adsorbing counterions.…”

Bis-NHC–Ag/Pd(OAc)2 Catalytic System Catalyzed Transfer Hydrogenation Reaction

“…Pd nanoparticles (Pd NPs) were formed by the decomposition of Pd-NHC bonds in a Pd/NHC catalytic system or by the reduction of the Pd precursor, especially in the presence of aliphatic amines such as triethylamine. The NHC-ligated Pd NPs present an efficient catalytic activity in the catalysis [44][45][46][47][48]. We recently reported an in situ-generated bis-NHC/Pd(OAc)2 catalytic system, which was derived from bis-benzimidazolium salt and Pd(OAc)2, as a catalyst for the Suzuki-Miyaura reaction, Mizoroki-Heck reaction, and Friedel-Crafts alkylation reaction of indole and nitrostyrene in good to excellent yields (Figure 1a) [49,50].…”