About Solid Phase vs. Liquid Phase in Suzuki-Miyaura Reaction

Deconvoluting Substrates, Support, and Temperature Effects on Leaching and Deactivation of Pd Catalysts: An In Situ Study in Flow

Leaching behavior of three different Pd heterogeneous catalysts (PdEnCat 30, FibreCat FC1001, and Pd/Al2O3) during the Heck reaction of iodobenzene and methyl acrylate, in the presence of triethylamine, was compared using a tandem flow reactor. While leaching was observed in all three cases, Pd/Al2O3 appeared to be the most robust, showing little/no leaching at ambient temperature. The leached Pd species also appear to display different catalytic activities. With a slight modification of the reactor, the leaching caused by individual components of the reaction mixture can be assessed separately. For the polymer-supported catalysts, triethylamine caused the largest amount of leaching, even at 30 °C. In contrast, the leaching from Pd/Al2O3 was observed only in the presence of iodobenzene at 90 °C. Variations in leaching behavior were ascribed to differences in Pd species and immobilization methods.

Functionalization of Fe3O4@SiO2 nanoparticles with Cu(i)-thiosemicarbazone complex as a robust and efficient heterogeneous nanocatalyst for N-arylation of N-heterocycles with aryl halides

In this research, the functionalized silica-coated magnetite nanoparticles with Cu(i)-thiosemicarbazone complex (Fe3O4@SiO2-[CuL]) has been designed and synthesized as a magnetically retrievable nanocatalyst. Different techniques were employed to characterize the structure of Fe3O4@SiO2-[CuL] comprising FT-IR, FE-SEM, TEM, DLS, XRD, EDX, TGA, AAS, and VSM analysis. The catalytic performance of Fe3O4@SiO2-[CuL] was perused in Ullmann-type N-arylation of nucleobases, xanthines, and other N-heterocycles with diverse aryl halides which acquired the desired N-aryl products in good to excellent yields. Fe3O4@SiO2-[CuL] is a thermal and chemical stable, easy to prepare and recyclable, inexpensive, and ecofriendly catalyst that needs no additional additive or ligand as promoters. This catalyst could be separated without difficulty by a simple magnet and reused for at least seven sequential runs without a significant decline in its catalytic performance.

Synthesis of fish scale derived hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for highly efficient synthesis of new benzimidazole-1,2,3-triazole hybrid analogues as antifungal agents

The preparation, characterization and application of hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for synthesis of new benzimidazole-1,2,3-triazole hybrid analogues as promising antifungal agents have been described. HASPBAEECC is fully characterized by different microscopic, spectroscopic and physical techniques, including scanning electron microscopy (SEM), transmission, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA) and FT-IR. The 'Click̕ Huisgen cycloaddition reaction of N-propargyl benzimidazole with diverse azidoalkyls in a THF-water media at ambient temperature provides the products in good-to-excellent yields using HASPBAEECC. HASPBAEECC is proved to be a stable, low cost, reusable and environmentally benign nanohybrid catalyst. The target compounds were screened against some pathogenic fungal comprising Candida albicans, Candida krusei, Candida parapsilosis, Aspergillus fumigatus and Aspergillus flavus in which it was determined that compounds 11f and 11 h have displayed promising antifungal activity similar to fluconazole as a reference drug. HASPBAEECC is a novel hybrid nano-catalyst for highly efficient synthesis of new benzimidazole-1,2,3- triazole hybrid analogues as antifungal agents.

3D Porous Polymeric-Foam-Supported Pd Nanocrystal as a Highly Efficient and Recyclable Catalyst for Organic Transformations

The efficient recovery of noble metal nanocrystals used in heterogeneous organic transformations has remained a significant challenge, hindering their use in industry. Herein, highly catalytic Pd nanoparticles (NPs) were first prepared having a yield of >98% by a novel hydrothermal method using PVP as the reducing cum stabilizing agent that exhibited excellent turnover frequencies of ∼38,000 h^-1 for Suzuki-Miyaura cross-coupling and ∼1200 h^-1 for catalytic reduction of nitroarene compounds in a benign aqueous reaction medium. The Pd NPs were more efficient for cross-coupling of aryl compounds with electron-donating substituents than with electron-donating ones. Further, to improve their recyclability, a strategy was developed to embed these Pd NPs on mechanically robust polyurethane foam (PUF) for the first time and a "dip-catalyst" (Pd-PUF) containing 3D interconnected 100-500 μm pores was constructed. The PUF was chosen as the support with an expectation to reduce the fabrication cost of the "dip-catalyst" as the production of PUF is already commercialized. Pd-PUF could be easily separated from the reaction aliquot and reused without any loss of activity because the leaching of Pd NPs was found to be negligible in the various reaction mixtures. We show that the Pd-PUF could be reused for over 50 catalytic cycles maintaining a similar activity. We further demonstrate a scale-up reaction with a single-reaction 1.5 g yield for the Suzuki-Miyaura cross-coupling reaction.

Thiosemicarbazone Complexes of Transition Metals as Catalysts for Cross-Coupling Reactions

Catalysis of cross-coupling reactions under phosphane-free conditions represents an important ongoing challenge. Although transition metal complexes based on the thiosemicarbazone unit have been known for a very long time, their use in homogeneous catalysis has been studied only relatively recently. In particular, reports of cross-coupling catalytic reactions with such complexes have appeared only in the last 15 years. This review provides a survey of the research in this area and a discussion of the prospects for future developments.

Palladium PEPPSI-IPr Complex Supported on a Calix[8]arene: A New Catalyst for Efficient Suzuki–Miyaura Coupling of Aryl Chlorides

We report here the synthesis and characterization of a new calix[8]arene-supported PEPPSI-IPr Pd polymetallic complex. This complex, showing greater steric hindrance around the Pd centers compared with previous calix[8]arene-based catalysts, demonstrated high reactivity and selectivity for the Suzuki–Miyaura coupling of aryl chlorides under mild conditions. Along with this good performance, the new catalyst showed low Pd leaching into the final Suzuki–Miyaura coupling products, indicative of a heterogeneous-type reactivity. This rare combination of good reactivity towards challenging substrates and low metal leaching offers great promise at both academic and industrial levels.

Kinetic Study of the Herrmann–Beller Palladacycle-Catalyzed Suzuki–Miyaura Coupling of 4-Iodoacetophenone and Phenylboronic Acid

This article presents an experimental kinetic study of the Suzuki–Miyaura reaction of 4-iodoacetophenone with phenylboronic acid catalyzed by the Herrmann–Beller palladacycle. This catalyst, together with the solvent (ethanol) and the base (sodium methylate), were chosen to ensure catalyst stability and reactants solubility all along the reaction. Based on the study of initial reaction rates, a quasi-first-order was found for 4-iodoacetophenone with a first-order dependence on the initial concentration of palladium. A zero-order was found for the base and the phenylboronic acid. The oxidative addition step of the mechanism was thus considered as the rate determining step. A global rate law was derived and validated quantitatively. A global activation energy, with an average value of ca. 63 kJ/mol was determined.

Calixarene-supported Pd–NHC complexes as efficient catalysts for scalable Suzuki–Miyaura cross-couplings

Calixarene-supported PEPPSI-catalysts deliver high yielding and almost Pd trace-free Suzuki–Miyaura coupling products.

Network-supported, metal-mediated catalysis: progress and perspective

This minireview focuses on recent developments of network-supported catalysts to improve the performance of a wide range of metal-mediated catalytic reactions.