Palladium Catalysts with Sulfonate-Functionalized-NHC Ligands for Suzuki−Miyaura Cross-Coupling Reactions in Water

Catalytic applications of zwitterionic transition metal compounds

This frontiers article highlights recent developments on the application of transition metal-based zwitterionic complexes in catalysis. Recent applications of selected zwitterionic catalysts in polymerization reactions, including the carbonylative polymerization of cyclic ethers, carbon-carbon coupling reactions, the asymmetric hydrogenation of unfunctionalized olefins, and the hydrofunctionalization of alkenes are reviewed. In addition, advances in the field of hydrogenation/dehydrogenation reactions related to energy applications, including the hydrogenation of CO₂ and the dehydrogenation of formic acid and N-heterocycles, the functionalization of CO₂ with amines and hydrosilanes, and the valorization of polyfunctional bio-based feedstocks, such as the dehygrogenation of glycerol to lactic acid or the reduction of levulinic acid into γ-valerolactone, are also described.

Palladium (II)-Salan Complexes as Catalysts for Suzuki-Miyaura C-C Cross-Coupling in Water and Air. Effect of the Various Bridging Units within the Diamine Moieties on the Catalytic Performance

Water-soluble salan ligands were synthesized by hydrogenation and subsequent sulfonation of salens (N,N'-bis(slicylidene)ethylenediamine and analogues) with various bridging units (linkers) connecting the nitrogen atoms. Pd (II) complexes were obtained in reactions of sulfosalans and [PdCl₄]^2-. Characterization of the ligands and complexes included extensive X-ray diffraction studies, too. The Pd (II) complexes proved highly active catalysts of the Suzuki-Miyaura reaction of aryl halides and arylboronic acid derivatives at 80 °C in water and air. A comparative study of the Pd (II)-sulfosalan catalysts showed that the catalytic activity largely increased with increasing linker length and with increasing steric congestion around the N donor atoms of the ligands; the highest specific activity was 40,000 (mol substrate) (mol catalyst × h)^-1. The substrate scope was explored with the use of the two most active catalysts, containing 1,4-butylene and 1,2-diphenylethylene linkers, respectively.

Transition-Metal-Mediated Modification of Biomolecules

The site-selective modification of biomolecules has grown spectacularly in recent years. The presence of a large number of functional groups in a biomolecule makes its chemo- and regioselective modification a challenging goal. In this context, transition-metal-mediated reactions are emerging as a powerful tool owing to their unique reactivity and good functional group compatibility, allowing highly efficient and selective bioconjugation reactions that operate under mild conditions. This Minireview focuses on the current state of organometallic chemistry for bioconjugation, highlighting the potential of transition metals for the development of chemoselective and site-specific methods for functionalization of peptides, proteins and nucleic acids. The importance of the selection of ligands attached to the transition metal for conferring the desired chemoselectivity will be highlighted.

Application of Palladium-Catalyzed Cross-Coupling Reactions in Organic Synthesis

:

Palladium-catalyzed cross-coupling reactions have gained a continuously growing interest of synthetic organic chemists. The present review gives a brief account of applications of the palladium-catalyzed cross-coupling reactions in comprehensive synthesis, viz., the Heck, Stille, Suzuki–Miyaura, Negishi, Sonogashira, Buchwald–Hartwig, Ullmann and the Oxidative, decarboxylative cross-coupling reactions, with particular emphasis on the synthesis of heterocyclic compounds.

Solubilization of Hydrophobic Catalysts Using Nanoparticle Hosts

A modular strategy for the solubilization and protection of hydrophobic transition metal catalysts using the hydrophobic pockets of water soluble gold nanoparticles is reported. Besides preserving original catalyst activity, this encapsulation strategy provides a protective environment for the hydrophobic catalyst and brings reusability. This system provides a versatile platform for the encapsulation of different hydrophobic transition metal catalysts, allowing a wide range of catalysis in water while uniting the advantages of homogeneous and heterogeneous catalysis in the same system.

Facile one-pot nanocatalysts encapsulation of palladium–NHC complexes for aqueous Suzuki–Miyaura couplings

Pd–NHC loaded nanocatalysts (NCs) were readily constructed by a facile one-pot self-assembly approach. These nanoparticles exhibited excellent catalytic activity in aqueous Suzuki–Miyaura couplings.

Tailoring the structure, pH sensitivity and catalytic performance in Suzuki–Miyaura cross-couplings of Ln/Pd MOFs based on the 1,1′-di(p-carboxybenzyl)-2,2′-diimidazole linker

Four Pd/Ln MOFs have been synthesized and tested as catalysts in Suzuki–Miyaura reactions in neat water, neat ethanol as well as water–ethanol mixtures.

A new diphosphine-carbonyl complex of ruthenium: an efficient precursor for C–C and C–N bond coupling catalysis

Reaction of 1,2-bis(diphenylphosphino)benzene (dppbz) with [{Ru(CO)₂Cl₂}_n] affords [Ru(dppbz)(CO)₂Cl₂], which serves as an excellent pre-catalyst for Suzuki-type C–C coupling and Buchwald-type C–N coupling reactions.

An efficient Pd-NHC catalyst system in situ generated from Na2PdCl4 and PEG-functionalized imidazolium salts for Mizoroki-Heck reactions in water

Three PEG-functionalized imidazolium salts L1–L3 were designed and prepared from commercially available materials via a simple method. Their corresponding water soluble Pd–NHC catalysts, in situ generated from the imidazolium salts L1–L3 and Na₂PdCl₄ in water, showed impressive catalytic activity for aqueous Mizoroki–Heck reactions. The kinetic study revealed that the Pd catalyst derived from the imidazolium salt L1, bearing a pyridine-2-methyl substituent at the N3 atom of the imidazole ring, showed the best catalytic activity. Under the optimal conditions, a wide range of substituted alkenes were achieved in good to excellent yields from various aryl bromides and alkenes with the catalyst TON of up to 10,000.

Synthesis of water-soluble palladium(ii) complexes with N-heterocyclic carbene chelate ligands and their use in the aerobic oxidation of 1-phenylethanol

Water-soluble palladium(ii) complexes with NHC chelate ligands have been prepared and studied as catalysts in the aerobic oxidation of alcohols in water.

Self-assembly of dinuclear Pd(ii)/Pt(ii) metallacyclic receptors incorporating N-heterocyclic carbene complexes as corners

A series of new Pd(ii)/Pt(ii) metallacycles were self-assembled in water, using bipyridinium-based ligands and kinetically-labile metal centers having chelating N-heterocyclic carbenes.

Hydrogen Production and Storage on a Formic Acid/Bicarbonate Platform using Water-Soluble N-Heterocyclic Carbene Complexes of Late Transition Metals

The synthesis and characterization of two water-soluble bis-N-heterocyclic carbene (NHC) complexes of rhodium and iridium is presented. Both compounds are active in H₂ generation from formic acid and in hydrogenation of bicarbonate to formate. The rhodium derivative is most active in both reactions, reaching a TOF of 39 000 h^-1 and a TON of 449 000 for H₂ production. The catalytic hydrogenation reactions were carried out in an autoclave system and analyzed using the integrated peak areas in the ¹ H NMR spectra. Decomposition of formic acid was investigated using a Fisher-Porter bottle equipped with a pressure transducer. Long-term stability for hydrogen evolution was tested by surveillance of the gas flow rate. The procedure does not require any additives like amines or inert gas conditions. Density functional theory calculations in agreement with experimental results suggest a bicarbonate reduction mechanism involving a second catalyst molecule, which provides an external hydride acting as reducing agent.