Phenoxylation of Alkynes through Mono‐ and Dual Activation Using Group 11 (Cu, Ag, Au) Catalysts

Hydrophenoxylation of alkynes by gold catalysts: a mini review

CONTEXT

The field of chemistry has significantly evolved, with catalysis playing a crucial role in transforming chemical processes. From Valerius' use of sulfuric acid in the sixteenth century to modern advancements, catalysis has driven innovations across various industries. The introduction of gold as a catalyst marked a pivotal shift, expanding its applications beyond ornamentation to homogeneous catalysis. Gold's unique properties, such as its electrophilic nature and flexibility, have enabled its use in synthesizing complex molecules, including those in nanomedicine and sustainable chemical processes. The development of gold-based complexes, particularly in hydroalkoxylation and hydroamination reactions, showcases their efficiency in forming carbon-oxygen bonds under mild conditions. Recent studies on dual gold catalysis and heterobimetallic complexes further highlight gold's versatility in achieving high turnover rates and selectivity. This evolution underscores the potential of gold catalysis in advancing environmentally sustainable methodologies and enhancing the scope of modern synthetic chemistry. The debate about the nature of monogold and dual-gold catalysis is open.

METHODS

DFT calculations have played a key role in promoting the activation of alkynes, in particular the hydrophenoxylation of alkynes by metal-based catalysts. They not only help identify the most efficient and selective catalysts but also aid in screening for those capable of performing a dual metal catalytic mechanism. The most commonly used functionals are BP86 and B3LYP, with the SVP and 6-31G(d) basis sets employed for geometry optimizations, and M06 with TZVP or 6-311G(d,p) basis sets used for single-point energy calculations in a solvent. Grimme dispersion correction has been explicitly added either in the solvent single point energy calculations or in the gas phase geometry optimizations or in both. To point out that M06 implicitly includes part of this dispersion scheme.

Synthesis and reactivity of N-heterocyclic carbene (NHC) gold-fluoroalkoxide complexes

We disclose a novel series of N-heterocyclic carbene (NHC) gold complexes with varied steric and electronic properties, bearing fluorinated alkoxide anions. Early reactivity studies involving these synthons, lead to the synthesis of various complexes of relevance to gold chemistry and catalysis.

Quantitative simulationSimulation of nitrogen doping effects on benzene selective adsorption by activated carbon in aqueous conditions

Investigating the impact of nitrogen doping on the selective adsorption of benzene on activated carbon under aqueous conditions holds significant importance in regulating nitrogen content on activated carbon precisely and enhancing benzene adsorption in the air. This study utilizes quantum chemical simulation to systematically compute the pairwise interactions of pyridine nitrogen, pyrrole nitrogen, graphite nitrogen, and their coexistence on carbon materials, including electrostatic potential, van der Waals potential, and polarity changes. We examine the adsorption of benzene and water on nitrogen-doped carbon materials and calculate the type and proportion of weak interactions in the adsorption process through energy decomposition analysis. Visual analysis of weak interactions is conducted via independent gradient scatter plots and isosurface plots. Based on this research, we investigate the influence of nitrogen doping on the competitive adsorption of benzene and water on carbon materials using adsorption energy and configuration changes. Our findings reveal that nitrogen doping disrupts the uniform electrostatic potential distribution and polarity of carbon materials. Specifically, graphite nitrogen inhibits water molecule adsorption by enhancing mutual repulsion and weakening dispersion and electrostatic interactions, consequently promoting benzene adsorption on carbon materials. Moreover, hydrogen bonds form between pyridine nitrogen, pyrrole nitrogen, and water, making carbon materials more hydrophilic. However, when combined with graphite nitrogen, this increases the negative van der Waals potential of carbon materials, further enhancing benzene adsorption. Experimental results align with the simulation, reinforcing the significance of this research in developing efficient activated carbon adsorbents for benzene under aqueous conditions.

Effect of oxygen functional groups on competitive adsorption of benzene and water on carbon materials: Density functional theory study

It is important to study the effect of oxygen-containing functional groups on the competitive adsorption mechanism of benzene and water on the surface of carbon materials, and to directional modification of activated carbon to improve its selective adsorption of benzene in air. In this study, the adsorption characteristics of benzene and water on original and linked ester, carboxyl, hydroxyl, carbon materials linked by ether groups were calculated by quantum chemical simulation based on density functional theory. The types and proportions of weak interactions in the adsorption process were calculated by energy decomposition analysis, and the adsorption mechanism of carbon materials for water and benzene was described. The influence and contribution of oxygen-containing functional groups on the adsorption of benzene and water were further analyzed by van der Waals potential and electrostatic potential, respectively, so as to determine the difference in the adsorption effect of different types of oxygen-containing functional groups on the two molecules. It was found that the carboxyl group has a great influence on the hydrophilicity of carbon materials, and the electrostatic potential distribution before and after linking the carboxyl group changed significantly. Therefore, they can attract each other with water through hydrogen bonds and occupy the surface adsorption sites of carbon materials, thereby inhibiting the adsorption of benzene on carbon materials. On the contrary, due to its hydrophobic properties, the ether group will free up adsorption space for the adsorption of benzene on the surface of the carbon material, which is beneficial to the adsorption of benzene. The adsorption experiments were carried out, and the results were consistent with the simulation. This study provides an idea for preparing efficient carbonaceous adsorbent of benzene and reducing benzene pollution in industry.

Towards Dual-Metal Catalyzed Hydroalkoxylation of Alkynes

Poly (vinyl ethers) are compounds with great value in the coating industry due to exhibiting properties such as high viscosity, soft adhesiveness, resistance to saponification and solubility in water and organic solvents. However, the main challenge in this field is the synthesis of vinyl ether monomers that can be synthetized by methodologies such as vinyl transfer, reduction of vinyl phosphate ether, isomerization, hydrogenation of acetylenic ethers, elimination, addition of alcohols to alkyne species etc. Nevertheless, the most successful strategy to access to vinyl ether derivatives is the addition of alcohols to alkynes catalyzed by transition metals such as molybdenum, tungsten, ruthenium, palladium, platinum, gold, silver, iridium and rhodium, where gold-NHC catalysts have shown the best results in vinyl ether synthesis. Recently, the hydrophenoxylation reaction was found to proceed through a digold-assisted process where the species that determine the rate of the reaction are PhO-[Au(IPr)] and alkyne-[Au(IPr)]. Later, the improvement of the hydrophenoxylation reaction by using a mixed combination of Cu-NHC and Au-NHC catalysts was also reported. DFT studies confirmed a cost-effective method for the hydrophenoxylation reaction and located the rate-determining step, which turned out to be quite sensitive to the sterical hindrance due to the NHC ligands.