New bis(N-heterocyclic carbene) palladium complex immobilized on magnetic nanoparticles: as a magnetic reusable catalyst in Suzuki-Miyaura cross coupling reaction

A magnetic palladium nickel carbon nanocomposite as a heterogeneous catalyst for the synthesis of distyrylbenzene and biphenyl derivatives

Distyrylbenzene and 9,10-distyrylanthracene derivatives were synthesized using an Fe₃O₄@Pd@Ni/C nanocomposite as a recyclable catalyst. The catalyst was recycled up to eight times.

Pd-N-heterocyclic carbene complex catalysed C–H bond activation of 2-isobutylthiazole at the C5 position with aryl bromides

An effective and efficient catalytic system has been reported for the synthesis of C5-arylated 2-isobutylthiazoles.

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

A critical review of conclusions about the putative heterogeneous mechanism in the Suzuki-Miyaura coupling by supported Pd solids is reported. In the first section, the turnover frequencies (TOF) of 20 well-established homogeneous catalysts are shown to be in the range 200 to 1,000,000,000 h − 1 . The evidences used to prove a heterogeneous mechanism are discussed and another interpretation is proposed, hypothesizing that only the leached species are responsible for the catalytic reaction, even at ppb levels. Considering more than 40 published catalytic systems for which liquid phase Pd content have been reported, activities have been computed based on leached Pd concentrations and are shown to be in the range TOF 150 to 70,000,000 h − 1 . Such values are compatible with those found for the well-established homogeneous catalysts which questions the validity of the conclusions raised by many papers about the heterogeneous (solid) nature of Suzuki-Miyaura catalysis. Last, a tentative methodology is proposed which involves the rational use of well-known tests (hot-filtration test, mercury test…) to help to discriminate between homogeneous and heterogeneous mechanisms.

Advances in Magnetic Nanoparticles-Supported Palladium Complexes for Coupling Reactions

Carbon‒carbon (C‒C) and carbon‒heteroatom (C‒X) bonds that form via transition-metal-catalyzed processes have been extensively used in the organic synthesis and preparation of natural products and important compounds such as heterocycles, biologically active molecules, and dendrimers. Among the most significant catalysts, magnetic nanoparticles-supported palladium complexes are very effective, versatile, and heterogeneous catalysts for a wide range of C‒C and C‒X coupling reactions due to their reusability, thermal stability, and excellent catalytic performance. In this review, recent advances to develop magnetic nanoparticles supported palladium complexes, including their preparation, characterization, catalytic application, and reusability in the formation of both C‒C and C‒X bonds, by authors such as Sonogashira, Heck, Suzuki‒Miyaura, and Stille, and a few examples concerning N-arylation, S-arylation, and Csp2-P coupling reactions are discussed.

The Current Status of Heterogeneous Palladium Catalysed Heck and Suzuki Cross-Coupling Reactions

In the last 30 years, C–C cross coupling reactions have become a reliable technique in organic synthesis due their versatility and efficiency. While drawbacks have been experienced on an industrial scale with the use of homogenous systems, many attempts have been made to facilitate a heterogeneous renaissance. Thus, this review gives an overview of the current status of the use of heterogeneous catalysts particularly in Suzuki and Heck reactions. Most recent developments focus on palladium immobilised or supported on various classes of supports, thus this review highlights and discuss contributions of the last decade.

Zwitterionic Rhodium and Iridium Complexes Based on a Carboxylate Bridge-Functionalized Bis-N-heterocyclic Carbene Ligand: Synthesis, Structure, Dynamic Behavior, and Reactivity

A series of water-soluble zwitterionic complexes featuring a carboxylate bridge-functionalized bis-N-heterocyclic carbene ligand of formula [Cp*M^IIICl{(MeIm)₂CHCOO}] and [M^I(diene){(MeIm)₂CHCOO}] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; M = Rh, Ir; MeIm = 3-methylimidazol-2-yliden-1-yl; diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd)) were prepared from the salt [(MeImH)₂CHCOO]Br and suitable metal precursor. The solid-state structure of both types of complexes shows a boat-shaped six-membered metallacycle derived of the κ²C,C' coordination mode of the bis-NHC ligand. The uncoordinated carboxylate fragment is found at the bowsprit position in the Cp*M^III complexes, whereas in the M^I(diene) complexes it is at the flagpole position of the metallacycle. The complexes [Rh^I(diene){(MeIm)₂CHCOO}] (diene = cod, nbd) exist as two conformational isomers in dichloromethane, bowsprit and flagpole, that interconvert through the boat-to-boat inversion of the metallacycle. An inversion barrier of ∼17 kcal·mol^-1 was determined by two-dimensional exchange spectroscopy NMR measurements for [Rh^I(cod){(MeIm)₂CHCOO}]. Reaction of zwitterionic Cp*M^III complexes with methyl triflate or tetrafluoroboric acid affords the cationic complexes [Cp*M^IIICl{(MeIm)₂CHCOOMe}]⁺ or [Cp*M^IIICl{(MeIm)₂CHCOOH}]⁺ (M = Rh, Ir) featuring carboxy and methoxycarbonyl functionalized methylene-bridged bis-NHC ligands, respectively. Similarly, complexes [M^I(diene){(MeIm)₂CHCOOMe}]⁺ (M = Rh, Ir) were prepared by alkylation of the corresponding zwitterionic M^I(diene) complexes with methyl triflate. In contrast, reaction of [Ir^I(cod){(MeIm)₂CHCOO}] with HBF₄·Et₂O (Et = ethyl), CH₃OTf, CH₃I, or I₂ gives cationic iridium(III) octahedral complexes [Ir^IIIX(cod){(MeIm)₂CHCOO}]⁺ (X = H, Me, or I) featuring a tripodal coordination mode of the carboxylate bridge-functionalized bis-NHC ligand. The switch from κ²C,C' to κ³C,C',O coordination of the bis-NHC ligand accompanying the oxidative addition prevents the coordination of the anions eventually formed in the process that remain as counterions.

A magnetic nanoparticle-supported N-heterocyclic carbene-palladacycle: an efficient and recyclable solid molecular catalyst for Suzuki-Miyaura cross-coupling of 9-chloroacridine

A robust magnetic nanoparticle-supported N-heterocyclic carbene-palladacycle has been readily synthesized by directly anchoring the structural defined acenaphthoimidazolylidene palladacycle with a long tail on magnetic nanoparticles (MNPs), and functioned as a solid molecular catalyst and exhibited extremely high catalytic activity towards the challenging Suzuki-Miyaura cross-coupling reactions between less-studied heterocyclic 9-chloroacridine and diverse boronic acids. Remarkably, the catalyst could be used 5 times without obvious loss of activity highlighting the efficiency of our strategy of immobilization of previledged catalysts.