Nature of the Copper-Oxide-Mediated C–S Cross-Coupling Reaction: Leaching of Catalytically Active Species from the Metal Oxide Surface

Divergent catalytic behaviors of assembled organogold(i) clusters derived from enyne cyclization

Homogeneous gold catalysis has attracted much recent attention due to diverse activation modes of gold(i) towards unsaturated organic groups. Because of attractive aurophilic interaction, structural transformations of metalated species into high nuclear clusters are often proposed in gold catalysis, while to date little is known about their assembly behaviors and catalytic activity. In this work, based on stoichiometric Au(i)-mediated enyne cyclization reactions, we achieve a discrete vicinal dicarbanion-centered Au4 intermediate and three assembled Au11, Au28, and Au14 clusters held together by several aryl dicarbanions. Spectral monitoring, kinetic and theoretical investigations confirm that these discrete and assembled intermediates display four different pathways upon catalyzing the cyclization reaction of the same 1,5-enyne substrate. The discrete Au4 cluster undergoes a full protodeauration process to generate active [Au(PPh3)]+ species for catalytic use. In contrast, the net-like Au11 cluster experiences a substrate-induced dissociation to generate a semi-stable Au10 unit and an active [alkyne-Au(PPh3)]+ fragment for further transformation. The dumbbell-like Au28 cluster is prone to cleavage of the central Au-Au linkage and each Au14 moiety exposes a coordination unsaturated site to activate a substrate molecule. However, the synthetic closed-Au14 cluster with full ligand protection is no longer catalytically active.

Multiple neighboring active sites of an atomically precise copper nanocluster catalyst for efficient bond-forming reactions

Atomically precise copper nanoclusters (NCs) are an emerging class of nanomaterials for catalysis. Their versatile core-shell architecture opens the possibility of tailoring their catalytically active sites. Here, we introduce a core-shell copper nanocluster (CuNC), [Cu29(StBu)13Cl5(PPh3)4H10]tBuSO3 (StBu: tert-butylthiol; PPh3: triphenylphosphine), Cu29NC, with multiple accessible active sites on its shell. We show that this nanocluster is a versatile catalyst for C-heteroatom bond formation (C-O, C-N, and C-S) with several advantages over previous Cu systems. When supported, the cluster can also be reused as a heterogeneous catalyst without losing its efficiency, making it a hybrid homogeneous and heterogeneous catalyst. We elucidated the atomic-level mechanism of the catalysis using density functional theory (DFT) calculations based on the single crystal structure. We found that the cooperative action of multiple neighboring active sites is essential for the catalyst's efficiency. The calculations also revealed that oxidative addition is the rate-limiting step that is facilitated by the neighboring active sites of the Cu29NC, which highlights a unique advantage of nanoclusters over traditional copper catalysts. Our results demonstrate the potential of nanoclusters for enabling the rational atomically precise design and investigation of multi-site catalysts.

C(sp)-C(sp3) Bond Formation through Ligand- and Additive-Free CuO-Mediated Decarboxylative Direct Cross-Coupling of Coumarin-/Chromone-3-carboxylic Acids and Terminal Alkynes

A practical and efficient method for the synthesis of functionalized 4-(aryl-/heteroaryl-ethynyl)chroman-2-ones and 2-(aryl-/heteroaryl-ethynyl)chroman-4-ones through copper-catalyzed decarboxylative direct cross-coupling of coumarin-/chromone-3-carboxylic acids with terminal alkynes, leading to the formation of C(sp)-C(sp3) bonds, has been unearthed. Advantages of this protocol include avoidance of any ligands and bases, a broad substrate scope, tolerance of diverse functional groups, and good to excellent yields.

Dinuclear complexes, a one dimensional chain and a two dimensional layer of bismuth(iii) chalcogenones for C–S cross coupling reactions

The bismuth coordination polymers derived from organochalcogenone ligands and their catalytic applications in the synthesis of annulated heterocyclic aryl thioethers have been investigated.

Comparative study of aryl halides in Pd-mediated reactions: key factors beyond the oxidative addition step

The comparative experimental study of Ar–X (X = Cl, Br, I) reactivity and analysis reported herein suggest that oxidative addition cannot be considered the sole reason of the observed low reactivity of aryl chlorides.

Copper(i) oxide nanoparticle-mediated C–C couplings for synthesis of polyphenylenediethynylenes: evidence for a homogeneous catalytic pathway

Polyphenylenediethynylenes have been synthesized using copper(i) oxide nanocatalysts under ligandless conditions, mild base, and atmospheric air as the oxidant in good yield and number average molecular weight.

Palladium nanoparticles as efficient catalyst for C-S bond formation reactions

The development of green, economical and sustainable chemical processes is one of the primary challenges in organic synthesis. Herein, we report an efficient and heterogeneous palladium-catalyzed sulfonylation of vinyl cyclic carbonates with sodium sulfinates via decarboxylative cross-coupling. Both aliphatic and aromatic sulfinate salts react with various vinyl cyclic carbonates to deliver the desired allylic sulfones featuring tri- and even tetrasubstituted olefin scaffolds in high yields with excellent selectivity. The process needs only 2 mol% of Pd2(dba)3 and the in situ formed palladium nano-particles are found to be the active catalyst.

Solid-State C-S Coupling in Nickel Organochalcogenide Frameworks as a Route to Hierarchical Structure Transfer to Binary Nanomaterials

In this work, the transfer of the flexible and easily tunable hierarchical structure of nickel organochalcogenides to different binary Ni-based nanomaterials via selective coupling of organic units was developed. We suggested the use of substituted aryl groups in organosulfur ligands (SAr) as traceless structure-inducing units to prepare nanostructured materials. At the first step, it was shown that the slight variation of the type of SAr units and synthetic procedures allowed us to obtain nickel thiolates [Ni(SAr)₂]_n with diverse morphologies after a self-assembly process in solution. This feature opened the way for the synthesis of different nanomaterials from a single type of precursor using the phenomenon of direct transfer of morphology. This study revealed that various nickel thiolates undergo selective C-S coupling under high-temperature conditions with the formation of highly demanding nanostructured NiS particles and corresponding diaryl sulfides. The in situ oxidation of the formed nickel sulfide in the case of reaction in an air atmosphere provided another type of valuable nanomaterial, nickel oxide. The high selectivity of the transformation allowed the preservation of the initial organochalcogenide morphologies in the resulting products.

Facile synthesis of 1,2-thiobenzonitriles via Cu-catalyzed denitrogenative radical coupling reaction

The first example of denitrogenative radical coupling with 3-aminoindazoles is presented. A diverse array of 1,2-thiobenzonitriles were obtained in good yields with wide substrate scope via oxidative C–N cleavage of 3-aminoindazoles.

Cu(I)–PNF, an organic-based nanocatalyst, catalyzed C–O and C–S cross-coupling reactions

Peptide nanofiber has been prepared via a self-assembly protocol and decorated with Cu(I) to prepare a nanostructural catalyst. The catalytic activity of this prepared nanomaterial (Cu(I)–PNF) was examined in C–O and C–S cross-coupling reactions. Compared with conventional copper–ligand catalytic systems, CuNP–PNF has unique advantages such as water solubility, high efficiency, and low cost, which makes it a highly efficient and beneficial catalyst to reuse in cross-coupling reactions.

pH-Control as a way to fine-tune the Cu/Cu2O ratio in radiation induced synthesis of Cu2O particles

In this work we have optimized the γ-radiation induced synthesis of Cu-Cu2O particles from aqueous CuSO4 solution by investigating the effect of pH. The obtained precipitate was analyzed by XRD and SEM techniques. The results indicated that at solution pH lower than 3.75, quasi-spherical Cu agglomerates can be formed while at pH higher than 4.40 only octahedron-shaped Cu2O particles are produced. At solution pH in the range from 3.75 to 4.40, a Cu-Cu2O mixture is produced. It was found that the relative amount of Cu2O in the Cu-Cu2O precipitate increases with pH in the studied range. The influence of solution pH on the Cu/Cu2O ratios in the product can be explained on the basis of pH-dependent competition kinetics between the reactions leading to either Cu or Cu2O formation. As a consequence, the composition and morphology of the Cu-Cu2O precipitate can be tuned by controlling pH of the aqueous CuSO4 solution during the γ-radiation induced synthesis.

Engineered C-S Bond Construction

Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.

C-H functionalization by high-valent Cp*Co(iii) catalysis

Significant progress has been accomplished in directed C-H functionalization through the use of earth-abundant and inexpensive first-row transition metals. Among these base metals, Co is especially attractive in view of its versatile applications in C-H functionalization, in both low- and high-valent states. In this vein, catalytic Co(iii) species can be generated from the dissociation of a Cp*Co(iii) catalyst or through the oxidation of a low-valent cobalt catalyst in the presence of an oxidant. In this feature article, we will discuss the breakthroughs in Cp*Co(iii)-promoted C-H functionalization. In this field, C(sp²)-H functionalization has been extensively studied and developed. In contrast, few C(sp³)-H functionalization reactions have been reported.

Efficient dehydrative alkylation of thiols with alcohols catalyzed by alkyl halides

Alcohols can be efficiently converted into the useful thioethers by a transition metal- and base-free dehydrative S-alkylation reaction with thiols or disulfides by employing alkyl halides as the effective catalyst. This simple and efficient method is a green and practical way for the preparation of thioethers, as it tolerates a wide range of substrates such as aryl and alkyl thiols, as well as benzylic, allylic, secondary, tertiary, and even the less reactive aliphatic alcohols.

Sulfonate, sulfide and thiolate ligands into an ultrasmall nanocluster: [Ag40.13Cu13.87S19(tBuS)20(tBuSO3)12]

A novel Ag–Cu bimetallic nanocluster, Ag_40.13Cu_13.87S₁₉(tBuS)₂₀(tBuSO₃)₁₂, has been synthesized by precise control.

Synthesis of Cu Nanoparticles: Stability and Conversion into Cu2S Nanoparticles by Decomposition of Alkanethiolate

A lean synthesis of copper nanoparticles (Cu NP) from CuCl₂ in dodecane via formation of Cu(I)-dodecanethiolate (Cu(I)-DDT) and their decomposition paths including spontaneous C-S bond cleavage of the alkanethiol on the surface of Cu NP is presented. The reduction of Cu(I)-DDT by the tert-butylamine-borane complex (TBAB) in dodecane under N₂ at elevated temperatures leads to the formation of thiol-protected Cu NP with narrow size distribution in the size range of 3-10 nm depending on the reaction conditions. The Cu NP in the presence of excess dodecanethiol reacts further to Cu₂S NP under decomposition of the ligand on the particle surface. The Cu₂S formation occurs after a short time at T > 175 °C or within ∼12 h at room temperature. If excess thiol is removed immediately after the synthesis, the resulting colloid shows irreversible aggregation within days or hours. Our results suggest that alkanethiols are not long-term stable on nanocopper surfaces and that the formation of copper(I) sulfide under the cleavage of the C-S bond occurs even at room temperature.

Formation of C–C, C–S and C–N bonds catalysed by supported copper nanoparticles

Copper nanoparticles on different supports are effective reusable catalysts for the palladium- and ligand-free coupling of aryl halides with alkynes, thiols and azoles.

Regiocontrolled direct C4 and C2-methyl thiolation of indoles under rhodium-catalyzed mild conditions

A straightforward and mild Rh(iii)-catalyzed remote C4 (sp²) and C2 (sp³)-methyl thiolation of an indole core was developed.