Sustainable Ligand-Free, Palladium-Catalyzed Suzuki-Miyaura Reactions in Water: Insights into the Role of Base

Ni/PiNe Heterogeneous Catalyst from Biomass Waste: Low-Loading, Ligand-Free Suzuki-Miyaura Cross-Coupling

An efficient Ni-based heterogeneous catalyst from pine needles urban waste valorization was designed and developed with a resource recycling strategy. The Ni/PiNe catalyst was fully characterized and tested in the Suzuki-Miyaura coupling under microwave irradiation. Although Ni is a promising candidate for replacing Pd-based catalytic systems, it generally requires a high catalyst amount and the exploitation of ligands and additives to enhance the reaction rate. On the contrary, with our new Ni/PiNe, 30 different products were efficiently synthesized with an isolated yield of up to 93 %, using a very low catalyst amount and in the absence of ligands. Furthermore, the Ni/PiNe catalyst also showed good durability for consecutive cycles and an impressive TON value (1140). In addition to the catalytic efficiency in short reaction time and to the stability and durability under MW irradiation, the Ni/PiNe allowed for further optimization, achieving a low E-factor value (14.0), thus highlighting the potential in further reducing the waste and costs associated to the process.

Mechanochemical Palladium-Catalyzed Cross-Coupling of Thianthrenium Salts and Arylboronic Acids

Cross-coupling reactions are indispensable for the construction of complex molecular scaffolds. In this work, we developed a sustainable methodology for the cross-coupling reaction of arene thianthrenium salts with aryl boronic acids, which can be effectively realized under mechanochemical conditions. Liquid-assisted grinding (LAG) enabled fast and high-yielding synthesis of a range of biaryls via Pd/RuPhos-catalyzed cross-coupling. The transformation works under ambient temperature and on air. Environmentally friendly solvent 2-methyltetrahydrofurane (Me-THF) was used as a LAG additive. Moreover, the major by-product of the cross-coupling reaction, thianthrene, can be recovered and reused.

Micellar catalysis: Polymer bound palladium catalyst for carbon-carbon coupling reactions in water

Metallosurfactants, defined here as hydrophobic metal-containing groups embedded in hydrophilic units when dispersed in water, emanate in the formation of metallomicelles. This approach continues to attract great interest for its ability to serve as micellar catalysts for various metal-mediated chemical transformations in water. Indeed, relevant to green chemistry, micellar catalysis plays a preeminent function as a replacement for organic solvents in a variety of chemical reactions. There are several methods for the interaction of metal complexes (catalysts or catalyst precursors) and surfactants for producing micellar aggregates. A very effective manner for achieving this involves the direct bonding of the metal center to the amphiphilic polymeric materials. Herein, we describe the synthesis of a metallosurfactant containing a palladium complex covalently incorporated into a CO2-based triblock polycarbonate derived using a dicarboxylic acid chain-transfer agent. This amphiphilic polycarbonate was shown to self-assemble in water to provide uniform and spherical micelles, where the catalytic metal center is located in the hydrophobic portion of the micelle. The resulting metallosurfactant was demonstrated to effectively catalyze carbon-carbon coupling reactions at very low catalyst loadings.

Metal-Micelle Interaction Leading to Spontaneous Formation of Ligand-Free Palladium(0) Nanoparticles: Highly Efficient Catalysis Enabling Biaryl Ketone Formation from Carboxylic Acid Derivatives

A novel strategy has been developed to spontaneously form ligand-free Pd(0) nanoparticles (NPs) from water- and air-sensitive Pd₂dba₃ in water. These NPs are thoroughly characterized by IR, NMR, and mass spectrometry, revealing that the metal-micelle binding plays a critical role in their stability and activity. High-resolution transmission electron microscopy supported the ultrasmall nature of NPs, whereas X-ray photoelectron spectroscopy analysis confirmed the zero-oxidation state of Pd. The shielding effect of micelles and enhanced stability of NPs enabled fast cross-couplings of water-sensitive triazine adducts of carboxylic acid to form nonsymmetrical biaryl ketones. These naturally formed NPs are more efficient than new synthetic NPs formed under a hydrogen atmosphere and traditional NPs formed using the air-sensitive Grignard reagent as a reductant. The activity of naturally formed NPs is compared with that of synthetic NPs over 34 substrates, revealing that naturally formed NPs are much more efficient than synthetic NPs.

The use of metal-organic frameworks as heterogeneous catalysts

This article presents an overview of some of the available research studies of MOFs as catalysts. Catalytic studies of magnetic iron oxide nanoparticles with modified surfaces, MOFs with precious metals such as palladium, platinum, and silver, with zirconium, hafnium, copper, alkaline earth metals, lanthanides are generalized. The studies of the catalytic activity of micro- and mesoporous MOF structures are described.

Synthesis of poly(9,9-dioctylfluorene) in a rotating packed bed with enhanced performance for polymer light-emitting diode

One of the most suitable methods for synthesizing conjugated polymers is the Suzuki cross-coupling reaction because of high tolerance and stability. Herein, we report an improved strategy to synthesize conjugated...

Catalyst-free synthesis of phenanthridines via electrochemical coupling of 2-isocyanobiphenyls and amines

One pot metal-free synthesis of phenanthridines and amides under electrochemical conditions.

New Trends in C-C Cross-Coupling Reactions: The Use of Unconventional Conditions

The ever-growing interest in the cross-coupling reaction and its applications has increased exponentially in the last decade, owing to its efficiency and effectiveness. Transition metal-mediated cross-couplings reactions, such as Suzuki-Miyaura, Sonogashira, Heck, and others, are powerful tools for carbon-carbon bond formations and have become truly fundamental routes in catalysis, among other fields. Various greener strategies have emerged in recent years, given the widespread popularity of these important reactions. The present review comprises literature from 2015 onward covering the implementation of unconventional methodologies in carbon-carbon (C-C) cross-coupling reactions that embodies a variety of strategies, from the use of alternative energy sources to solvent- free and green media protocols.

Zeolite-Enhanced Sustainable Pd-Catalyzed C-C Cross-Coupling Reaction: Controlled Release and Capture of Palladium

Supported palladium catalysts have attracted significant attention for use in cross-coupling reactions due to their recyclability. However, the inevitable progressive loss of Pd that occurs in the catalytic process deactivates the catalysts, which hinders their sustainable application. Herein, we report a zeolite-enhanced sustainable Pd catalyst for C-C cross-coupling reactions. Zeolite does a good job of acting as a sink for Pd²⁺ ions. This catalyst exhibits an excellent homogeneous catalytic performance by releasing Pd species from zeolite. In addition, the Pd²⁺ ions were successfully recaptured in a controlled catalytic system by combining the uniform microporous structure and good adsorption features of zeolite. The release/capture mechanism of the Pd species guaranteed the high loading and high dispersion of Pd on the recycled catalyst. The 0.84%Pd@USY catalysts were reused at least 10 times in water without an appreciable reduction in activity. This study presents a new perspective toward the design of a highly efficient and sustainable supported metal catalyst.