Catalytic C–H bond functionalisation chemistry: the case for quasi-heterogeneous catalysis

Abstract

This feature article examines the potential of heterogeneous Pd species to mediate catalytic C-H bond functionalisation processes employing suitable substrates (e.g. aromatic/heteroaromatic compounds). A focus is placed on the reactivity of supported and non-supported Pd nanoparticle (PdNPs) catalysts, in addition to the re-appropriation of well-established heterogeneous Pd catalysts such as Pd/C. Where possible, reasonable comparisons are made between PdNPs and traditional 'homogeneous' Pd precatalyst sources (which form PdNPs). The involvement of higher order Pd species in traditional cross-coupling processes, such as Mizoroki-Heck, Sonogashira and Suzuki-Miyaura reactions, allows the exemplification of potential future topics for study in the area of catalytic C-H bond functionalisation processes.

Plausible role of nanoparticle contamination in the synthesis and properties of organic electronic materials

“…Recent studies of catalytic reactions have surprisingly shown that catalytically active metal complexes do not remain unchanged during the synthetic transformation [14,15]. Indeed, several transformations involving metal complexes do take place simultaneously with the catalytic reaction ( Figure 4) [14].…”

Definition of green synthetic tools based on safer reaction media, heterogeneous catalysis, and flow technology

“…Among the different approaches for the definition of catalytic methodologies, the use of insoluble catalysts that operate in a heterogeneous fashion is highly intriguing and also challenging [48][49][50][51][52][53]. Significant advantages may derive from the adoption of this strategy with the reduction of waste produced, provided that an easy recovery and reuse of the catalyst is achieved.…”

Pdo.o2Ceo.98O2: a copper- and ligand-free quasi-heterogeneous catalyst for aquacatalytic Sonogashira cross-coupling reaction

“…Hg(0) is known to form amalgams with a variety of metals in their zero oxidation state (Reay and Fairlamb, 2015). Hence, if Pd dissociates from the solid Pd 0.02 Ce 0.98 O 2-, it would bind with Hg(0) thereby quenching its catalytic activity.…”

“…However, the leaching of palladium from the catalyst is still the main problem, even though most researchers have reported that their catalysts can be recycled by the redeposition of Pd onto the support (Redon, Peña and Crescencio, 2014). This is due to the quasi-heterogeneous mechanism of the Sonogashira cross-coupling reaction via the solvated palladium clusters (Reay and Fairlamb, 2015).…”

“…Hence, if Pd dissociates from the solid Pd 0.02 Ce 0.98 O 2-, it would bind with Hg(0) thereby quenching its catalytic activity. However, Pd in a raised oxidation state is not expected to be quenched by Hg(0) (Reay and Fairlamb, 2015). Thus, the mercury-poisoning test was used to establish whether bare Pd(0) did participate in catalysing the Sonogashira coupling reactions.…”