Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Research and industrial interest in radical C–H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C–H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M–R groups, and coupling of radical cations with nucleophiles (Nu).

Recent Advances in Radical C-H Activation/Radical Cross-Coupling.

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

Cu-catalysed arylation reactions devoted to the formation of C–C and C–heteroatom bonds (Ullmann-type couplings) have acquired great importance in the last decade. This review discusses the history and development of coupling reactions between aryl halides and various classes of nucleophiles, focusing mostly on the different mechanisms proposed through the years. Selected mechanistic investigations are treated more in depth than others. For example, evidence in favour or against radical mechanisms is discussed. Cu(I) and Cu(III) complexes involved in the Ullmann reaction and N/O selectivity in aminoalcohol arylation are discussed. A separate section has been dedicated to the synthesis of heterocyclic rings through intramolecular couplings. Finally, recent developments in green chemistry for these reactions, such as reactions in aqueous media and heterogeneous catalysis, have also been reviewed.

https://pubs.rsc.org/en/content/getauthorversionpdf/C3CS60289C

Copper catalysed Ullmann type chemistry: From mechanistic aspects to modern development

A novel silver-mediated highly selective oxidative C-H/C-H functionalization of 1,3-dicarbonyl compounds with terminal alkynes for the creation of polysubstituted furans and pyrroles in one step has been demonstrated. Promoted by the crucial silver species, perfect selectivity and good to excellent yields could be achieved. This protocol represents an extremely simple and atom-economic way to construct polysubstituted furans and pyrroles from basic starting materials under mild conditions.

Silver-Mediated Oxidative C–H/C–H Functionalization: A Strategy To Construct Polysubstituted Furans

The selective radical/radical cross-coupling of two different organic radicals is a great challenge due to the inherent activity of radicals. In this paper, a copper-catalyzed radical/radical C sp 3 H/P H cross-coupling has been developed. It provides a radical/radical cross-coupling in a selective manner. This work offers a simple way toward β-ketophosphonates by oxidative coupling of aryl ketone o -acetyloximes with phosphine oxides using CuCl as catalyst and PCy 3 as ligand in dioxane under N 2 atmosphere at 130 °C for 5 h, and yields ranging from 47 % to 86 %. The preliminary mechanistic studies by electron paramagnetic resonance (EPR) showed that, 1) the reduction of ketone o -acetyloximes generates iminium radicals, which could isomerize to -sp 3 -carbon radical species; 2) phosphorus radicals were generated from the oxidation of phosphine oxides. Various aryl ketone o -acetyloximes and phosphine oxides were suitable for this transformation.

Copper-Catalyzed Radical/Radical C(sp 3)-H/P-H Cross-Coupling: α-Phosphorylation of Aryl Ketone O-Acetyloximes.

Oxidative cross-coupling/cyclization to build polysubstituted pyrroles from terminal alkynes and β-enamino esters.

Insights toward the Cu-catalyzed C–C coupling reaction were investigated through operando IR and in situ X-ray absorption near-edge structure/extended X-ray absorption fine structure. It was found that the Cu(I) complex formed from the reaction of CuI with β-diketone nucleophile was liable under the cross-coupling conditions, which is usually considered as active catalytic species. This labile Cu(I) complex could rapidly disproportionate to the spectator Cu(II) and Cu(0) species under the reaction conditions, which was an off-cycle process. In this copper-catalyzed C–C coupling reaction, β-diketone might act both as the substrate and the ligand.

Labile Cu(I) Catalyst/Spectator Cu(II) Species in Copper-Catalyzed C–C Coupling Reaction: Operando IR, in Situ XANES/EXAFS Evidence and Kinetic Investigations

Jie Ke

Papers

Silver-Mediated Oxidative C–H/C–H Functionalization: A Strategy To Construct Polysubstituted Furans

Copper-Catalyzed Radical/Radical C(sp 3)-H/P-H Cross-Coupling: α-Phosphorylation of Aryl Ketone O-Acetyloximes.

Oxidative cross-coupling/cyclization to build polysubstituted pyrroles from terminal alkynes and β-enamino esters.

Labile Cu(I) Catalyst/Spectator Cu(II) Species in Copper-Catalyzed C–C Coupling Reaction: Operando IR, in Situ XANES/EXAFS Evidence and Kinetic Investigations

Synergistic Catalysis in the Sonogashira Coupling Reaction: Quantitative Kinetic Investigation of Transmetalation