Phosphine-free Conditions Research Articles

Palladium-immobilized triazine dendrimer on magnetic nanoparticles: as reusable microreactor for solvent-dependent synthesis strategy of 2,3-diphenylindoles and pentaphenylpyrrole derivatives

In this work, we demonstrate that palladium-immobilized triazine dendrimer on magnetic nanoparticles in proper solvents, provides an impressive, atom-economical and compelling approach for the selective synthesis of 2,3-diphenylindole or pentaphenylpyrrole derivatives via annulation of diphenylacetylene with diverse anilines. Both the annulation methods were taken place under copper- and phosphine-free conditions with high yields at air atmosphere. Likewise, bis-indoles were obtained with excellent yields under optimized reaction conditions. Besides, the catalyst was isolated and reused for seven cycles without decrease potential of catalytic activity. Two mechanistic pathways were proposed and geometry optimizations, electronic properties as well as vibrational characterizations of all structures were performed with density functional theory (DFT). Also, the investigation of atomic basin properties of these molecular systems was carried out utilizing the quantum atoms-in-molecules theory (QTAIM). The results showed that 2,3-diphenylindole and pentaphenyl pyrrole molecular systems can be used as intramolecular acceptor/donor (n-like/p-like) sections.

Tetradentate copper complex supported on boehmite nanoparticles as an efficient and heterogeneous reusable nanocatalyst for the synthesis of diaryl ethers

In this work boehmite nanoparticles (BNPs) were prepared through addition of aqueous solution of NaOH to solution of Al(NO3)3·9H2O. Then, the surface of BNPs was modified by (3-chloropropyl)trimethoxysilane (CPTMS) and further tetradentate ligand (MP-bis(AMP)) was anchored on its surface. At final step, a tetradentate organometallic complex of copper was stabilized on the surface of modified BNPs (Cu(II)-MP-bis(AMP)@boehmite). These obtained nanoparticles were characterized using SEM imaging, WDX, EDS, AAS and TGA analysis, BET method, FT-IR spectroscopy, and XRD pattern. In continue, the catalytic activity of Cu(II)-MP-bis(AMP)@boehmite has been used as a much efficient, reusable and hybrid of organic–inorganic nanocatalyst in the synthesis of ether derivatives through C–O coupling reaction under palladium-free and phosphine-free conditions. Cu(II)-MP-bis(AMP)@boehmite catalyst has been recovered and reused again for several times in the synthesis of ether derivatives.

Atomically dispersed palladium catalyses Suzuki\u2013Miyaura reactions under phosphine-free conditions

Single-atom catalysts have emerged as a new frontier in catalysis science. However, their applications are still limited to small molecule activations in the gas phase, the classic organic transformations catalyzed by single-atom catalysts are still rare. Here, we report the use of a single-atom Pd catalyst for the classic Suzuki–Miyaura carbon–carbon coupling reaction under phosphine-free and open-air conditions at room temperature. The single-atom Pd catalyst is prepared through anchoring Pd on bimetal oxides (Pd-ZnO-ZrO2). The significant synergetic effect of ZnO and ZrO2 is observed. The catalyst exhibits high activity and tolerance of a wide scope of substrates. Characterization demonstrates that Pd single atoms are coordinated with two oxygen atoms in Pd-ZnO-ZrO2 catalyst. The catalyst can be fabricated on a multi-gram scale using a simple in situ co-precipitation method, which endows this catalytic system with great potential in practical applications.

A Highly Selective Manganese-Catalyzed Synthesis of Imines under Phosphine-Free Conditions

An efficient and highly selective phosphine-free NN-manganese(I) complex catalyst system was developed for the acceptorless dehydrogenative coupling of alcohols with amines to form imines. The coupling reactions underwent at 3 mol % catalyst loading, and a large range of alcohols and amines with diverse functional groups was applied, including challenging diol and diamine. The target imine products were obtained in good to excellent yields. The present work provides an alternative method to construct highly active nonprecious metal complex catalysts based on phosphine-free ligands.

Synthesis of 2-Substituted Benzo[b]furans/furo-Pyridines Catalyzed by NiCl2

The first Ni-catalyzed tandem synthesis of 2-substituted benzo[b]furans/furo-pyridines from 2-halophenols and 1-alkynes was explored under Cu-free and phosphine-free conditions. The protocol was carried out with NiCl2/5-nitro-1, 10-phenanthroline in DMA (N,N-dimethylacetamide) at 120 °C. It was found to be simple, cost effective, and have a wide substrate scope. Additionally, the method is compatible with heteroaryl substrates, resulting in the formation of 2-substituted benzo[b]furans/furo-pyridines in reasonable to good yields.

A polymer-supported salen-palladium complex as a heterogeneous catalyst for the Mizoroki-Heck cross-coupling reaction

In this work, the catalytic performance of a polymer-supported Pd(II)-salen complex (PS-Pd-salen) as an effective and environmentally friendly catalyst for the Mizoroki-Heck CC cross-coupling reaction is presented. The PS-Pd-salen complex was employed as a catalyst for Mizoroki-Heck reactions of an aryl halide with various terminal alkenes (Styrene, Methyl acrylate, Ethyl acrylate, n-butyl acrylate, tert-Butyl acrylate) under phosphine free conditions. Moreover, a range of Mizoroki-Heck reactions using different polar solvents, co-solvents, and bases has been investigated. Aryl iodides and bromides with terminal alkene are well activated in CC coupling reactions. All products were isolated by column chromatography as liquids/white to off-white crystalline solids and confirmed by 1H and 13C NMR spectroscopy. The catalyst could be easily separated by filtrations and reusability of catalyst was also assessed under optimized conditions. The hot filtration test revealed that the catalyst was truly heterogeneous, very active and stable under the reaction conditions and could be reused up to fifth cycles with analogous activities to that of the fresh catalyst. High catalytic activity at a low concentration (30 mg) and flexibility under mild reaction conditions, simple product work-up towards Mizoroki-Heck reactions indicated that PS-Pd-salen was an efficient catalyst for CC coupling reactions.

Supported organometallic palladium catalyst into mesoporous channels of magnetic MCM-41 nanoparticles for phosphine-free C C coupling reactions

Abstract Magnetic MCM-41 nanoparticles were synthesized via Fe3O4-doped into mesoporous channels of MCM-41 nanoparticles and further, a new organometallic complex of palladium was supported on its inner surface (Pd-imi@MCM-41/Fe3O4). This immobilized catalyst was applied as highly efficient, heterogeneous and magnetically recoverable nanocatalyst in the various C C coupling reactions such as Suzuki–Miyaura and Mizoroki-Heck reactions under phosphine-free conditions at atmospheric pressure. This catalyst has advantages of both magnetic nanoparticles and mesoporous materials. The structure of prepared nanomaterial has been characterized by various techniques such as N2 adsorption–desorption isotherms, TEM, SEM, EDS, WDX, FT-IR, XRD, TGA, ICP, AAS, and VSM. SEM images of this catalyst demonstrate that the particles size are less than 100 nm in diameter. VSM curve of the catalyst shows that this catalyst can be recovered using an external magnet; therefore, this catalyst can be reused for several times without significant loss of its catalytic efficiency or palladium leaching. Also, all products were obtained in high TON and TOF numbers, which reveals this catalyst has high activity and selectivity in described coupling reactions. Heterogeneity and stability of this nanocatalyst were confirmed by hot filtration test and AAS technique.

Functionalized graphene oxide anchored to Ni complex as an effective recyclable heterogeneous catalyst for Sonogashira coupling reactions

The Sonogashira cross coupling reaction is an applied method for preparation of diarylethyne compounds from readily available aryl halide derivatives and phenyl acetylene. The coupling reaction using nickel complex of N,N′-Bis(2-hydroxyethyl)ethylenediamine onto core shell graphene oxide (GO@SiO2-BHED-Ni) as a catalyst was studied in this research. This heterogonous catalyst showed good thermal stability, highly efficiency and recyclability in the reaction. Moreover, the catalyst is simply separated and can be reused several times without significant loss of catalytic activity. A wide range of aryl halides was coupled successfully under palladium and phosphine free conditions. The use of this catalyst led to the formation of substituted aromatic alkynes in excellent yields and short reaction times.

Novel oxime-palladacycle supported on clay composite as an efficient heterogeneous catalyst for Sonogashira reaction

A novel supported catalyst formed by an oxime-derived palladacycle supported on clay OxPdCy@clay is synthesized and characterized. This palladium composite promotes the Sonogashira reaction of aryl iodides, bromides and chlorides with terminal alkynes in polyethylene glycol200 at 85 or 130 °C using 0.05–0.1 mol% of palladium loading under copper and phosphine free conditions. This supported palladacycle, OxPdCy@clay, showed a superior catalytic activity than dimeric oxime-palladacycles. Mechanistic studies about the heterogeneous or homogeneous nature of the catalyst show that catalyst is working mainly under heterogeneous conditions. This supported palladacycle OxPdCy@clay can be recycled by simple centrifugation and reused for at least nine consecutive runs with small decrease in activity.

Manganese-Catalyzed β-Alkylation of Secondary Alcohols with Primary Alcohols under Phosphine-Free Conditions

Manganese(I) complexes bearing a pyridyl-supported pyrazolyl-imidazolyl ligand efficiently catalyzed the direct β-alkylation of secondary alcohols with primary alcohols under phosphine-free conditions. The β-alkylated secondary alcohols were obtained in moderate to good yields with water formed as the byproduct through a borrowing hydrogen pathway. β-Alkylation of cholesterols was also effectively achieved. The present protocol provides a concise atom-economical method for C–C bond formation from primary and secondary alcohols.

Phosphines as Silylium Ion Carriers for Controlled C–O Deoxygenation: Catalyst Speciation and Turnover Mechanisms

We report studies delineating the speciation, kinetics, and deoxygenation catalysis of phosphine-modified mixtures of B(C6F5)3 (BCF) and R3SiH. Combinations of BCF, a tertiary silane, and PAr3 generate the [H–B(C6F5)3–][R3Si–PAr3+] ion pair with conversions that depend on the silane and the phosphine. Smaller silanes enhance the ionization of the Si–H, as judged by heteronuclear NMR spectroscopy. Kinetic studies indicate that from BCF·PPh2(p-tol), formation of the borohydride/silyl phosphonium ion pair is α [Et3SiH]1[PPh2(p-tol)]0. DFT calculations confirmed the intermediacy of the weakly coordinated BCF···H–SiEt3 adduct en route to the silyl phosphonium. For the catalytic deoxygenation of anisole with Et3SiH, phosphine additives slow the reaction relative to phosphine-free conditions. In situ monitoring confirmed the presence of [H–B(C6F5)3–][Et3Si–PAr3+] at early times, but this slowly converts to [H–B(C6F5)3–][H3C–PAr3+], which is catalytically inactive. These data are reconciled by invoking a competit...

Heck-type olefination and Suzuki coupling reactions using highly efficient oxacalix[4]arene wrapped nanopalladium catalyst

A simple one-pot method is used for the synthesis of water dispersible and stable palladium nanoparticles (PdNps) where oxacalix[4]arene dihydrazide (OXDH) is used as both a reducing and capping agent. The OXDH-PdNps have been characterized by UV–Visible spectroscopy, Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The OXDH-PdNps are spherical in shape with an average size of 3–4 nm and well crystallized in a face centered cubic structure. The capping of the OXDH ligand on the nanoparticles surface was evaluated using FT-IR. The OXDH-PdNps have been used in carbon–carbon coupling reactions, namely, the Suzuki–Miyaura and Mizoroki–Heck reactions. Both of the reactions are carried out under phosphine-free conditions to provide better yields. The nanocatalyst can be easily recovered and reused for six consecutive catalytic cycles without any significant loss in its catalytic activity.

Synthesis of palladium nanoparticles with leaf extract of Chrysophyllum cainito (Star apple) and their applications as efficient catalyst for C\u2013C coupling and reduction reactions

A simple green chemical method for the one-step synthesis of palladium nanoparticles (PdNPs) has been described by reducing palladium (II) chloride with the leaf extract of Chrysophyllum cainito in aqueous medium. The synthesis of the palladium nanoparticles completed within 2–3 h at room temperature, whereas on heat treatment (70–80 °C), the synthesis of colloidal PdNPs completed almost instantly. The stabilized PdNPs have been characterized in detail by spectroscopic, electron microscopic and light scattering measurements. The synthesized PdNPs have been utilized as a green catalyst for C–C coupling reactions under aerobic and phosphine-free conditions in aqueous medium. In addition, the synthesized PdNPs have also been utilized as a catalyst for a very efficient sodium borohydride reduction of 3- and 4-nitrophenols. The synthesized PdNPs can retain their catalytic activity for several months.

Role of Surface Basic Sites in Sonogashira Coupling Reaction over Ca5(PO4)3OH Supported Pd Catalyst: Investigation by Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Hydroxyapatite [Ca5(PO4)3(OH); HAP] supported Pd catalyst has been identified as an efficient and reusable heterogeneous catalyst for the Sonogashira coupling reaction under copper and phosphine-free conditions. The 2 wt % Pd/HAP offered excellent yields (96%) compared to 2 wt % Pd/MgO and 2 wt % Pd/Al2O3 catalysts. The formic acid adsorbed diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results revealed that moderate basic sites on 2 wt % Pd/HAP are found to be selective for the Sonogashira coupling reaction. Strong basic sites present on the Pd/MgO catalyst demonstrated homocoupling of the substrate during the Sonogashira reaction. The physicochemical characteristics of the catalysts are rationalized by temperature-programmed desorption of CO2, H2-temperature-programmed reduction, formic acid adsorbed DRIFTS, Brunnauer–Emmet–Teller surface area, X-ray photoelectron spectroscopy, transmission electron microscopy, and CO chemisorption techniques. The 2 wt % Pd/HAP catalyst was recover...

Palladium Stabilized by Amino-Vinyl Silica Functionalized Magnetic Carbon Nanotube: Application in Suzuki–Miyaura and Heck–Mizoroki Coupling Reactions

This study describes an investigation on Suzuki and Heck cross-couplings of aryl electrophiles in the presence of heterogeneous Pd nanoparticles supported on amino-vinyl silica functionalized magnetic carbon nanotube. The core–shell contains CNT@Fe3O4@SiO2-Pd in which the functionalized SiO2 helps the stabilization of Pd nanoparticles and also responsible for the reduction of Pd(II) to Pd(0) without the need for adding external reducing agents. All of the reactions were done under phosphine-free condition.

Direct arylation polycondensation of β-unprotected chalcogen heteroles under phosphine-free conditions

We have demonstrated a direct arylation polycondensation of β-unprotected chalcogen heteroles (furan, thiophene and selenophene) under phosphine-free conditions. The polycondensation of furan and thiophene using a solid-supported palladium catalyst, Pd/C, gave alternating copolymers (Mn = 8000–10000), but the polycondensation of these monomers using common palladium catalysts such as Pd(OAc)2 gave insoluble polymeric products resulting from β-defects and network formation. Selenophene was a less reactive monomer for direct arylation using these catalysts, Pd/C and Pd(OAc)2, yielding low molecular weight copolymer (Mn < 2500). On the other hand, PdCl2 was the most effective catalyst for the polycondensation of selenophene. The high molecular weight polymer (Mn = 11800) could be obtained. The 1H NMR and UV-vis absorption spectra of the polymers obtained from furan, thiophene and selenophene were similar to those of the polymers synthesized by Suzuki-Miyaura cross-coupling polycondensation.

Environmentally-Safe Conditions for a Palladium-Catalyzed Direct C3-Arylation with High Turn Over Frequency of Imidazo[1,2-b]pyridazines Using Aryl Bromides and Chlorides.

Pd(OAc)2 was found to catalyze very efficiently the direct arylation of imidazo[1,2-b]pyridazine at C3-position under a very low catalyst loading and phosphine-free conditions. The reaction can be performed in very high TOFs and TONs employing as little as 0.1-0.05 mol % catalyst using a wide range of aryl bromides. In addition, some electron-deficient aryl chlorides were also found to be suitable substrates. Moreover, 31 examples of the cross couplings were reported using green, safe, and renewable solvents, such as pentan-1-ol, diethylcarbonate or cyclopentyl methyl ether, without loss of efficiency.

New magnetically recoverable palladium-based catalysts active in the alkoxycarbonylation of iodobenzene

Abstract New magnetically recoverable catalysts have been synthesized by deposition of 1% palladium (Pd)-metal on the polymer poly(1-oxo-trimethylene), containing 15% of magnetite. The magnetite allows the complete recovery of the catalyst with the simple application of an external magnetic field. The activity of such a catalyst has been studied under phosphine-free conditions in the alkoxycarbonylation of iodobenzene to the corresponding benzoic acid esters.

Synthesis of Pd-Complex Supported on MCM-41 and Its Catalytic Activity for the C–C Coupling Reactions

An efficient, novel and reusable heterogenized palladium catalyst was prepared on MCM-41 mesoporous. The prepared mesoporous catalyst was characterized by XRD, FT-IR, SEM, TGA, BET and ICP-OES techniques. This catalyst applied as an excellent nano catalyst for the Suzuki reactions in PEG and H2O as an environmentally friendly solvents under phosphine-free conditions. The catalyst was easily recovered and reused for several times without significant loss of its catalytic efficiency. Also the turn over frequency effects of various reaction parameters on the Suzuki reactions and leaching of palladium are herein discussed.

ChemInform Abstract: NIS‐Catalyzed Oxidative Cyclization of Alcohols with Amidines: A Simple and Efficient Transition‐Metal Free Method for the Synthesis of 1,3,5‐Triazines.

AbstractA wide range of 1,3,5‐triazines is efficiently synthesized via the title reaction of amidines (I) with benzyl alcohols under mild transition‐metal and phosphine free conditions without the need of oxygen in good yields.