Synthesis of BiarylsviaLigand-Free Suzuki-Miyaura Cross-Coupling Reactions: A Review of Homogeneous and Heterogeneous Catalytic Developments

Recyclable LaF3·Pd nanocatalyst in Suzuki coupling: green synthesis of biaryls from haloarenes and phenylboronic acids

Herein we prepared the novel LaF3·Pd nanocatalyst characterized by XRD and TEM analysis. The nanocatalyst was applied in Suzuki coupling reaction for the synthesis of biaryls in aqueous medium from readily available aryl halides (bromides and iodides) and substituted phenylboronic acids in the presence of K2CO3 as the base at 70 °C. The present method is capable of giving the C-C coupled product in good to excellent yields (up to 97%). The reactions were conducted under green conditions in aqueous medium and the nanocatalyst used in this study was recyclable. The recyclability and reusability of the catalyst was checked for seven consecutive cycles without significant loss in reactivity.

Recent Advancements in Continuous-Flow Suzuki-Miyaura Coupling Utilizing Immobilized Molecular Palladium Complexes

Immobilized Pd-catalyzed Suzuki-Miyaura coupling under continuous-flow conditions using a packed-bed reactor, representing an efficient, automated, practical, and safe technology compared to conventional batch-type reactions. The core objective of this study is the development of an active and durable catalyst. In contrast to supported Pd nanoparticles, the attachment of Pd complexes onto solid supports through well-defined coordination sites is considered a favorable approach for preparing highly dispersed and stabilized Pd species. These species can be directly employed in various flow reactions without the need for pre-treatment. This concept paper explores recent achievements involving the application of immobilized Pd complexes as precatalysts for continuous-flow Suzuki-Miyaura coupling. Our focus is to elucidate the significance of the designed catalyst structures in relation to their catalytic performance under flow conditions. Additionally, we highlight various reaction systems and catalyst packing methods, emphasizing their crucial roles in establishing a practical synthesis process.

Palladium(II)-immobilized Triptycene based Hypercrosslinked Polymers: An Efficient, Green, and Reusable Heterogenous Catalyst for Suzuki-Miyaura Cross-coupling Reaction

The Suzuki-Miyaura cross-coupling (SMCC) involves the coupling of organohalides and organoboron molecules in the presence of Pd(II)-based catalysts. Often SMCC reactions employ homogenous catalysts. However, such homogenous SMCC reactions are associated with certain limitations which has motivated design of effective and sustainable Pd(II)-based heterogeneous catalytic systems. Herein, we report a systematic development of a Pd(II)-immobilized and triptycene based ionic hyper crosslinked polymer (Pd@TP-iHCP) and explored its application as a heterogeneous catalyst for SMCC reaction. Pd@TP-iHCP has ample N-heterocyclic carbene (NHC) pendants that anchor Pd(II) centres on the polymeric matrix. Pd@TP-iHCP was characterized satisfactorily using FT-IR, 13 C CP-MAS NMR, BET surface area analysis, SEM, EDX and HRTEM. The performance of Pd@TP-iHCP as a heterogeneous catalyst for SMCC reactions was explored using various combinations of aryl boronic acids and aryl halides. Experimental results show that Pd@TP-iHCP is associated with a moderately high surface area. It is an efficient catalyst for SMCC (in aqueous media) with a modest loading of 0.8 mol % Pd(II)-catalyst since high yields of the expected products were obtained in shorter time intervals. Pd@TP-iHCP also features excellent stability and catalyst recyclability since it could be re-used for several cycles without any significant decrease in catalytic efficiency.

Pretransmetalation Intermediates in Suzuki-Miyaura Cross-Couplings: Synthesis of Csp3-, Csp2- and Csp-Organopalladium(II) Boronates

Organopalladium(II) boronates represent fundamental pretransmetalation intermediates in Suzuki-Miyaura cross-couplings. These species are typically kinetically unstable, making them particularly elusive. In this study, a range of unprecedented, kinetically stable alkyl-, alkenyl-, allenyl-, and alkynylpalladium(II) boronates were prepared from various C_sp³, C_sp², and C_sp electrophiles via a simple, general method. The structures of these complexes were secured by X-ray crystallography, and the chemical competence of a number of these intermediates in transmetalation was demonstrated.

Electro- and photoactivation of silver-iron oxide particles as magnetically recyclable catalysts for cross-coupling reactions

Colloidal Ag particles decorated with Fe3O4 islands can be electrochemically or photochemically activated as inverse catalysts for C(sp2)-H heteroarylation. The silver-iron oxide (SIO) particles are reduced into redox-active forms by cathodic charging at mild potentials or by short-term light exposure, and can be reused multiple times by magnetic cycling without further activation. A negative shift in the reduction peak is attributed to an overpotential produced by surface Fe3O4 which separates residual Ag ions or clusters from bulk silver. The catalytic efficiency of SIO is maintained even with acid degradation, which can be countered simply by adding water to the reaction medium.

TiO2-Modified Montmorillonite-Supported Porous Carbon-Immobilized Pd Species Nanocomposite as an Efficient Catalyst for Sonogashira Reactions

In this study, a combination of the porous carbon (PCN), montmorillonite (MMT), and TiO₂ was synthesized into a composite immobilized Pd metal catalyst (TiO₂-MMT/PCN@Pd) with effective synergism improvements in catalytic performance. The successful TiO₂-pillaring modification for MMT, derivation of carbon from the biopolymer of chitosan, and immobilization of Pd species for the prepared TiO₂-MMT/PCN@Pd⁰ nanocomposites were confirmed using a combined characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption isotherms, high-resolution transition electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was shown that the combination of PCN, MMT, and TiO₂ as a composite support for the stabilization of the Pd catalysts could synergistically improve the adsorption and catalytic properties. The resultant TiO₂-MMT₈₀/PCN₂₀@Pd⁰ showed a high surface area of 108.9 m²/g. Furthermore, it exhibited moderate to excellent activity (59-99% yield) and high stability (recyclable 19 times) in the liquid-solid catalytic reactions, such as the Sonogashira reactions of aryl halides (I, Br) with terminal alkynes in organic solutions. The positron annihilation lifetime spectroscopy (PALS) characterization sensitively detected the development of sub-nanoscale microdefects in the catalyst after long-term recycling service. This study provided direct evidence for the formation of some larger-sized microdefects during sequential recycling, which would act as leaching channels for loaded molecules, including active Pd species.

Suitably Band-aligned MOF derived Ni2P/MnO2 Heterostructure With Ni(+1) Coordination Surface Sites For Self-Coupling of Aryl Halides to Bi-aryls

An efficient photo-redox route for the aryl-aryl self-coupling of aryl halides through a heterogeneous catalysis route has been demonstrated. Coordinatively unsaturated Ni 2 P surface with enhanced photochemical credentials upon hetero-structuring with δ-MnO 2 affects the organic transformation to biaryls with impressive yield and photo-conversion efficiency. Duel role of Ni 2 P catalyst with its participation as the catalytic active surface and the photo-redox centre distinguishes the organic transformation achieved herein with the other catalytic and photo-catalytic aryl-aryl self-coupling.

Enhancement of the catalytic activity of Suzuki coupling reactions by reduction of modified carriers and promotion of Pd/H2-PrxOy surface electron transfer

Pd/H2-PrxOy nanotubes were prepared by electrostatic spinning, high-temperature calcination and modified deposition–precipitation method, and exhibited high catalytic performance for Suzuki coupling reaction under mild conditions.

Palladium Nanoparticles Supported on Cellulosic Paper as Multifunctional Catalyst for Coupling and Hydrogenation Reactions

Hallmark of a successful catalyst is its high efficiency, economic aspects, operational simplicity, extensive reusability, higher environment friendliness, and potential use in multiple industrial applications. Herein, a facile protocol involving a catalyst with Pd nanoparticles supported on cellulose paper (also known as a "dip-catalyst") for the hydrogenation of a series of quinolines, nitroarene, and C-C bond formation reactions in most benign solvents such as water is described. The mere insertion/removal of the "dip-catalyst" strip enables instantaneous start/stop of the reaction, which enhances its reusability and ease of separation of products. Cellulose paper (CP) strips decorated with Pd nanoparticles (Pd/CP) are prepared by the reduction of K₂ PdCl₄ soaked strips using formic acid as reductant. The resulting spherical shaped Pd particles, confirmed by scanning electron microscopy, form stable catalysis centers on the support. XRD signature confirms the crystallinity of the Pd nanoparticles and the TEM images display 15-20 nm size particles uniformly decorating CP. X-ray photoelectron spectroscopy indicates the formation of metallic Pd. The catalyst is tested for the C-C bond formation reactions. Pd/CP catalyzed Suzuki-Miyaura coupling reaction demonstrate >99% conversion with optimum selectivity. On the other hand, Mizoroki-Heck reaction produced 87% conversion with the reaction of 4-methoxycarbonyl phenylboronic acid and iodobenzene in ethanol:water (1 : 1 v/v) using KOH as base. The developed Pd/CP construct produces >99% of the pyridine-ring hydrogenated product on quinoline hydrogenation using tetrahydroxydiboron (THDB) as the hydrogen source. Diverse and highly reducible functional groups were also evaluated for transfer hydrogenation, which demonstrates a high efficiency in terms of both reactivity and selectivity. The used catalysts are recyclable for the multiple cycles.

Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

The Suzuki-Miyaura reaction (the cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as a useful synthetic organic reaction that forms a C(sp²)-C(sp²) bond. The catalytic cycle of the reaction involves the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. It migrates the aryl and alkenyl groups of boronic acid to Pd and produces a Pd-C bond. Many studies have investigated the mechanism of transmetalation. They elucidated the mechanism of the organometallic reaction and its role as a fundamental step in catalytic reactions. This perspective reviews studies on the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. Emphasis was laid on the structures and chemical properties of the intermediate Pd complexes and the effects of OH^- on the pathways of the catalytic Suzuki-Miyaura reaction. The reactions of arylboronic acids with Rh(I)-OH complexes were investigated, which are relevant to the mechanism of Rh-catalysed addition of aryl boronic acids to enones and aldehydes. Recent studies on the transmetalation of boronic acids with other late transition metals such as Fe(II), Co(I), Pt(II), Au(III), and Au(I) are presented with the related catalytic reactions and their utilisation in the synthesis of aromatic molecules and π-conjugated materials.

New Palladium - ZrO2 Nano-Architectures from Thermal Transformation of UiO-66-NH2 for Carbonylative Suzuki and Hydrogenation Reactions

The new nanocomposites, Pd/C/ZrO₂ , PdO/ZrO_2, and Pd/PdO/ZrO₂ , were prepared by thermal conversion of Pd@UiO-66-Zr-NH₂ (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO₂ or C/ZrO₂ matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr-NH₂ . The most active PdO/ZrO₂ composite, formed benzophenone with TOF up to 1600 h^-1 , while by using Pd@UiO-66-Zr-NH₂ , much lower TOF values, 51-95 h^-1 , were achieved. After the reaction, PdO/ZrO₂ was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO₂ and PdO/ZrO₂ catalysts under microwave irradiation.

A recyclable self-supported nanoporous PdCu heterogeneous catalyst for aqueous Suzuki-Miyaura cross-coupling

Nanoporous PdCu (NP-PdCu) was prepared by the dealloying strategy from a PdCuAl ternary alloy precursor and characterized systematically using SEM, TEM, XRD, and XPS. NP-PdCu was demonstrated to be a competent self-supported heterogenous catalyst for Suzuki-Miyaura cross-coupling, affording a series of synthetically valuable biaryl compounds in good to excellent yields. This catalyst could be easily separated from the product via centrifugation and reused several times without obvious loss of catalytic performance.

Highly Dispersed Pd Clusters Anchored on Nanoporous Cellulose Microspheres as a Highly Efficient Catalyst for the Suzuki Coupling Reaction

With the depletion of nonrenewable resources such as oil/coal/gas, more and more research studies began to focus on the high-value utilization of residual biomass resources. Herein, for the first time, honeycomb nanoporous microspheres fabricated from renewable biomass resources of cellulose were used as a carrier to fabricate a highly dispersed palladium (Pd) nanocatalyst. Various physicochemical characterizations presented convincing pieces of evidence for the good dispersion of Pd clusters with a mean diameter of 1.6 nm. As the carrier, cellulose microspheres with an interconnected nanoporous structure contributed to the adhesion and dispersion of Pd particles, and their rich hydroxyl groups could fix the Pd particles. Importantly, the cellulose matrix could in situ induce the formation of metallic Pd(0) during calcination without a reductant. The cellulose/Pd catalyst was applied to the Suzuki coupling reaction, which exhibited promising catalytic activity compared to commercial Pd/C and unsupported homogeneous Pd(OAc)₂ catalysts, as well as good stability. The utilization of the residual biomass resource to build catalyst materials would be important for the sustainable chemistry.

Synthesis of Arylpalladium(II) Boronates: Confirming the Structure and Chemical Competence of Pre-transmetalation Intermediates in the Suzuki-Miyaura Reaction

Palladium(II) boronates are recognized as fundamental pre-transmetalation intermediates in Suzuki-Miyaura cross-couplings. While these typically transient species have been detected and studied spectroscopically, it is conspicuous that they have never been isolated since this important reaction was discovered over forty years ago. This study reports the synthesis of a family of unprecedented arylpalladium(II) boronates that are, by design, kinetically stable at ambient temperature, both in solution and in the solid state. These properties enabled unambiguous crystallographic confirmation of their structure for the first time and their chemical competence in a Suzuki-Miyaura reaction was demonstrated.

Amine-Tagged Fragmented Ligand Installation for Covalent Modification of MOF-74

MOF-74 is one of the most explored metal-organic frameworks (MOFs), but its functionalization is limited to the dative post-synthetic modification (PSM) of the monodentate solvent site. Owing to the nature of the organic ligand and framework structure of MOF-74, the covalent PSM of MOF-74 is very demanding. Herein, we report, for the first time, the covalent PSM of amine-tagged defective Ni-MOF-74, which is prepared by de novo solvothermal synthesis by using aminosalicylic acid as a functionalized fragmented organic ligand. The covalent PSM of the amino group generates metal binding sites, and subsequent post-synthetic metalation with Pd^II ions affords the Pd^II -incorporated Ni-MOF-74 catalyst. This catalyst exhibits highly efficient, size-selective, and recyclable catalytic activity for the Suzuki-Miyaura cross-coupling reaction. This strategy is also useful for the covalent modification of amine-tagged defective Ni₂ (DOBPDC), an expanded analogue of MOF-74.

Prospects and Applications of Palladium Nanoparticles in the Cross-coupling of (hetero)aryl Halides and Related Analogues

Discovering efficient methods for the formation of carbon-carbon bonds is a central ongoing theme in organic synthesis. Cross-coupling reactions catalysed by metal nanoparticles are attractive alternatives to the traditional use of metal counterparts due to the catalytic tunability, selectivity, recyclability and reusability of the nanoparticles. The ongoing search for sustainable processes demands that reusable and environmentally benign catalysts are used. While the advantages of nanoparticles catalysts over bulk catalysts cannot be overemphasised, the problem of sintering, agglomeration and leaching are drawbacks to their full industrial applications. Hence, efforts are being made towards advancing the efficiency of the catalytic nanoparticle systems over the years. This review presents the progress, the challenges and the prospects of palladium nanoparticle with focus on Heck, Suzuki, Hiyama and Sonogashira cross-coupling reactions involving (hetero) aryl halides and the analogues.

Tetra-arylborate lipophilic anions as targeting groups

Tetraphenylborate (TPB) anions traverse membranes but are excluded from mitochondria by the membrane potential (Δψ). TPB-conjugates also distributed across membranes in response to Δψ, but surprisingly, they rapidly entered cells. They accumulated within lysosomes following endocystosis. This pH-independent targeting of lysosomes makes possible new classes of probe and bioactive molecules.

Ionic liquid immobilized Cu(I)–hydrazone–triphenylphosphine complex: an easily recyclable catalytic system for Suzuki and Heck cross couplings

A highly efficient, reusable, catalytic system of Heck and Suzuki cross-coupling reactions was observed for an inexpensive copper complex dispersed in ethyl-methyl imidazolium hexafluorophosphate medium, [EMIM]PF6. The reaction conditions were optimized by studying the effects of temperature, catalyst concentration, solvent, and time. This method functions for a variety of substrates towards the cross-coupling reactions. Most notably, the catalyst – ionic liquid mixture was easily recoverable and reused six times without much loss in the catalytic activity, causing a notably very low impact on the environment.

Understanding and Improving Photocatalytic Activity of Pd-Loaded BiVO4 Microspheres: Application to Visible Light-Induced Suzuki-Miyaura Coupling Reaction

The effective utilization of visible light is required for exploiting photocatalytic reactions in indoor and outdoor environments. In this study, Pd-supported BiVO₄ microspheres (Pd-BiVO₄) were prepared for visible light-induced photocatalytic reactions. Under irradiation with a white light-emitting diode, the obtained Pd-BiVO₄ composite exhibited considerably improved catalytic activity for the decomposition of an organic dye compared with other BiVO₄ catalysts. The Pd-BiVO₄ composite was also effective for catalytic organic transformation via the visible light-induced Suzuki-Miyaura coupling reaction. The photogenerated electrons in the conduction band of BiVO₄ flowed to the Pd nanoparticles and amplified cross-coupling reaction. The influence of the crystal structure and grain size of BiVO₄ and the role of the deposited Pd nanoparticles were fully investigated to elucidate the visible light activity of the catalyst. This system highlights the possibility of an indoor light source with low energy density for sustainable organic transformations.

Palladium catalyzed desulfurative coupling of allyl sulfides with organoboronic acids

A palladium catalyzed desulfurative coupling of allylthioethers with organoboronic acids under mild reaction conditions is described.

Recent advances in the functionalization of polyfluoro(aza)aromatics via C-C coupling strategies

Polyfluoro(aza)aromatic compounds are of interest in various fields of practical applications, such as medicinal and agrochemistry, materials science and advanced technologies. The C-C coupling reactions are known to be a promising synthetic tool to create challenging fluorinated molecules of diverse architectures. In this review, we have summarized the recent advances in the functionalization of polyfluoro(aza)aromatics via both transition metal-catalyzed and metal-free C-C coupling reactions for the period from 2006 to the beginning of 2021. Also, mechanistic features for chemical transformations of fluoroarene scaffolds and new opportunities for practical applications of the designed fluorinated molecules have been highlighted.

Synthesis of ortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids

An efficient palladium-catalyzed denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids is described. The reaction affords various ortho-aryl and alkenylated benzamides in good to high yields.

Silica–sulfuric acid and alumina–sulfuric acid: versatile supported Brønsted acid catalysts

–SO3H functionalized silica and alumina have emerged as efficient and eco-compatible heterogeneous solid acid catalysts for the construction of various important molecular skeletons.

An easily fabricated palladium nanocatalyst on magnetic biochar for Suzuki–Miyaura and aryl halide cyanation reactions

A sustainable biochar material for the synthesis of a novel heterogeneous catalyst for organic reactions is reported.

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

A metal-free route for the synthesis of biarenes has been developed. The approach is based on the photoextrusion of a phosphate moiety occurring upon irradiation of biaryl- and triaryl phosphates. The reaction involves an exciplex as the intermediate and it is especially suitable for the preparation of electron-rich biarenes.

Ni/Pd-catalyzed Suzuki-Miyaura cross-coupling of alcohols and aldehydes and C-N cross-coupling of nitro and amines via domino redox reactions: base-free, hydride acceptor-free

Domino oxidation-Suzuki-Miyaura cross-coupling of benzyl alcohols with phenylboronic acid and domino reduction-C-N cross-coupling of the nitro compounds with aryl halides were carried out using a strong Ni/Pd bimetallic redox catalyst. The catalyst bearing a copolymer with two Ni/Pd coordinated metals in porphyrin (derived from demetalated chlorophyll b) and salen-type ligands, and pyridine moiety as a base functionality all immobilized on magnetite NPs was synthesised and characterized. The domino oxidation cross-coupling reaction was accomplished under molecular O2 in the absence of any hydride acceptor or/and base. Also, the domino reduction C-N cross-coupling reaction was performed in the presence of NaBH4 without the need for any base and co-reductant. This multifunctional catalyst gave moderate to good yields for both coupling reactions with high chemoselectivity. A wide investigation was conducted to determine its mechanism and chemoselectivity.