Oxime Palladacycle Research Articles

Oxime Palladacycle Supported on Magnetic Meoporous Silica: An Efficient Catalyst for Copper‐Free Acyl Sonogashira Reaction

AbstractThe catalytic activity of the supported bis(oxime palladacycle) catalyst was evaluated in the acyl Sonogashira reaction. The reaction conditions, such as solvent, base, and palladium content, were screened to achieve the best catalytic performance. Tetrahydrofuran (THF) solvent, triethylamine (Et3N) base, and the reaction temperature of 110 °C were found to be ideal for achieving high yields of the desired products. Furthermore, a catalyst loading of only 0.22 mol% palladium was sufficient to achieve good conversion. Broad ranges of aryl acetylenes and benzoyl chlorides were successfully coupled to give the desired acetylenic ketones. The reaction appeared to proceed efficiently using a small amount of catalyst. The magnetic property of the catalyst allowed for easy separation using an external magnet. The catalyst was stable and reused for multiple reaction runs without a significant deactivation. After seven cycles, the catalyst maintained over 90 % of its initial catalytic activity.

A copper- and amine-free sonogashira reaction catalyzed by a supported bis(oxime palladacycle) on magnetized SBA-15

The recently reported magnetic catalyst, Fe3O4@SBA-bis(oxime palladacycle), was incorporated in the Sonogashira reaction. The potential catalytic activity of the catalyst was evaluated by optimizing the reaction conditions. It was discovered that using dimethylsulfoxide (DMSO) as a solvent, a catalyst loading of 0.25 mol% palladium, Cs2CO3 as a base, and a reaction temperature of 120 °C resulted in the highest yields. The catalyst showed excellent activity with a wide range of aryl halides and aryl acetylenes in the Sonogashira reaction. The use of a low catalyst loading further highlighted its efficiency. Moreover, the catalyst demonstrated noteworthy reusability by consistently preserving its activity and stability through seven successive runs. The magnetic properties of the catalyst allowed for easy separation and recovery.

Bis(Oxime Palladacycle) Supported on Magnetized SBA-15 as an Efficient and Retriveble Catalyst for the Mizoroki–Heck Reaction

Bis(Oxime Palladacycle) Supported on Magnetized SBA-15 as an Efficient and Retriveble Catalyst for the Mizoroki–Heck Reaction

Still Elusive – Pd(II)‐Mediated Base Pairing by an Acetophenone Oxime Palladacycle within 15N‐Labelled Double‐Helical Oligonucleotides

AbstractBoth α and β anomers of an acetophenone C‐nucleoside were synthesized and incorporated in the middle of short oligodeoxynucleotides. The ketone oligonucleotides were converted to 15N‐labelled oxime oligonucleotides by treatment with 15N‐hydroxylamine and, finally, cyclopalladated by treatment with lithium tetrachloropalladate. Comparison of the UV melting profiles of duplexes bearing the β anomer of either the palladacyclic or the metal‐free oxime C‐nucleoside suggested formation of a stable Pd(II)‐mediated base pair, especially with adenine or thymine as the base pairing partner. Melting profiles of the corresponding duplexes bearing the α anomer were much more convoluted, precluding meaningful comparison. 15N NMR spectra were obtained for the β anomeric oxime oligonucleotide as well as its palladacyclic derivative but the signals unfortunately diminished below detection limit when the latter was hybridized with a complementary strand placing a 15N3‐labelled thymine opposite to the palladacyclic residue.

A new family of oxime palladacycles mixed with unsymmetrical phosphorus ylides; synthesis, structural, cytotoxicity and catalytic activity studies

In the present investigation, the reactivity of an oxime-derived palladacycle [Pd{C,N–C6H4{C(Me) = NOH}-2}(μ-Cl)]2 toward various unsymmetrical phosphorus ylides has been studied. When the ylide was added to a solution of oxime complex in dichloromethane (2:1 ratio), the new oxime palladacycles of the types [Pd{C,N–C6H4{C(Me) = NOH}-2}(Ph2PCH2PPh2C(H)C(O)C6H4X)]ClO4 (X = Cl (1), Br (2), NO2(3) or OCH3 (4)) were formed by means of bridge-splitting reaction. These are the first description of oxime-based palladacycles mixed with phosphorus ylides. All of complexes were fully characterized by elemental analysis, IR and NMR spectroscopies. The crystal structure of 3 were determined by single-crystal X-ray diffraction analysis that confirmed breaking of Pd–Cl bonds in the initial precursor and allowing phosphorus ylide act as P,C-chelating ligand. In addition, the catalytic activity of 3 was evaluated in the Suzuki cross-coupling reactions of a variety of arylbromides with phenylboronic acid. This complex was also used for the assessment of their anticancer activities against three human carcinoma cell lines: A549 (human lung carcinoma), HT29 (human colon carcinoma), and HeLa (human cervical carcinoma). The results show that the new family of oxime-derived palladacycles could be introduced as promising innovative anticancer complexes and considered as an efficient catalyst in the cross coupling reactions.

Mono‐ and dinuclear oxime palladacycles bearing diphosphine ligands: An unusual coordination mode for dppe

Three new oxime‐based palladacycles, namely [Pd{C,N‐C6H4{C(Me)NOH}‐2}(dppm)]ClO4 (1), [Pd2{C,N‐C6H4{C(Me)NOH}‐2}2(dppe)2(μ‐dppe)](ClO4)2 (2) and [Pd{C,N‐C6H4{C(Me)NOH}‐2}(dppmS2)]ClO4 (3), were synthesized by the reaction of dinuclear oxime complex [Pd{C,N‐C6H4{C(Me)NOH}‐2}(μ‐Cl)]2 with different diphosphine ligands (dppm, dppe and dppmS2). The synthesized complexes were characterized using Fourier transform infrared, 31P NMR, 1H NMR and 13C NMR spectroscopic methods and elemental analyses, and their molecular structures were elucidated using X‐ray crystallography. The structure of 2 is worthy of note as it is the first oxime palladacycle where there are both bridging (P–) and chelating (P^P) dppe ligands, giving rise to a dinuclear complex. The palladium atom is in a five‐coordinate, square pyramidal P3NC environment, while in 3 the palladium atom is in a distorted square planar environment, coordinated by the oxime ligand and a chelating (S^S) dppmS2 ligand. These complexes were employed as efficient catalysts for the Suzuki–Miyaura cross‐coupling reaction of several aryl bromides with phenylboronic acid. The in vitro cytotoxicity of the compounds was also evaluated against human tumour cell lines (HT29, A549 and HeLa) using the MTT assay method. The results indicate that the dinuclear complex 2 has greater catalytic and anticancer activity in comparison with the mononuclear complexes 1 and 3.

Oxime palladacycle in PEG as a highly efficient and recyclable catalytic system for phenoxycarbonylation of aryl iodides with phenols

In this report, we have developed a sustainable protocol for the synthesis of aromatic esters by a carbonylative method using di‐μ‐chlorobis [5‐hydroxy‐2‐[1‐(hydroxyimino‐ĸN) ethyl] phenyl‐ĸC] palladium (II) dimer (1) catalyst in PEG‐400 as a greener and recyclable solvent. The reaction is carried out at room temperature using CO in a balloon. Good to excellent yield of various esters can be synthesize using this protocol. Direct insertion of CO moiety leads to the high atom and step economy. Compared to previous protocol this phosphine free approach for the synthesis of aromatic esters provides high Turnover Number (TON) and Turnover Frequency (TOF). Developed approach has an alternative route for use of conventional palladium precursor with high conversion and selectivity. The catalyst system and product can easily be separated using diethyl ether as a solvent. The Pd/PEG‐400 system could be reused up to a fifth consecutive cycle without any loss of its activity and selectivity.

Microwave-assisted C-C coupling reaction using polymer-supported electron-rich oxime palladacycles in aqueous condition

Abstract Previously reported polymer-supported oxime palladacycle catalyst has shown effective catalytic activity in the Suzuki coupling reaction. In this work, the effect of microwave on reaction rate and induction period was examined by comparing them with the conventional heating. Undoubtedly, microwave heating effectively enhanced the catalytic performance in the Suzuki reaction. In-depth observation of the kinetic profiles revealed that the microwave irradiation not only reduced the overall reaction time but also significantly decreased the induction period to less than 3 min. Finally, the performance of the catalyst in water, coupling of potassium phenyltrifluoroborate and aryl bromides, and recyclability were also examined.

Graphene Oxide-Supported Oxime Palladacycles as Efficient Catalysts for the Suzuki–Miyaura Cross-Coupling Reaction of Aryl Bromides at Room Temperature under Aqueous Conditions

Palladacycles are highly efficient precatalysts in cross-coupling reactions whose immobilization on carbonaceous materials has been hardly studied. Herein, we report a detailed study on the synthesis and characterization of new oxime palladacycle-graphene oxide non-covalent materials along with their catalytic activity in the Suzuki–Miyaura reaction. Catalyst 1-GO, which has been fully characterized by ICP, XPS, TGA, and UV-Vis analyses has been demonstrated to be an efficient catalyst for the Suzuki–Miyaura coupling between aryl bromides and arylboronic acids using very low catalyst loadings (0.002 mol % of Pd) at room temperature under aqueous conditions.

Oxime Palladacycle Catalyzed Carbonylative Sonogashira Cross‐Coupling with High Turnovers in PEG as a Benign and Recyclable Solvent System

AbstractOxime palladacycles‐ di‐μ‐chlorobis [5‐chloro‐2‐[(4‐ chlorophenyl)(hydroxyimino‐κN) methyl] phenyl‐κC] palladium (II) dimer (1) and di‐μ‐chlorobis [5‐hydroxy‐2‐[1‐(hydroxyimino‐κN) ethyl] phenyl‐κC] palladium (II) dimer (2) provide a phosphine free approach for the synthesis of ynones at low palladium loadings (10−5 mol%) thus resulting in catalytic turnover numbers (TONs) and turnover frequencies (TOFs) of the order of 106. Oxime palladacycle 1 shows TON 587 times and TOF 331 times higher than the best palladium catalyst reported in the literature for the carbonylative cross‐coupling between 4‐iodoanisole and phenylacetylene as a model reaction. The use of poly (ethylene glycol) as an environmentally benign solvent system allows the recyclability of the oxime palladacycle at low palladium loading up to four times. Further, the oxime palladacycles are advantageous in effecting higher conversion and selectivity at low palladium loadings as compared to conventional palladium precursors‐ Pd (OAc)2 and PdCl2(PPh3)2

ChemInform Abstract: Magnetic Nanoparticles Supported Oxime Palladacycle as a Highly Efficient and Separable Catalyst for Room Temperature Suzuki—Miyaura Coupling Reaction in Aqueous Media.

AbstractA novel magnetic nanoparticle‐supported oxime palladacycle catalyst is successfully prepared and characterized.

Magnetic nanoparticles supported oxime palladacycle as a highly efficient and separable catalyst for room temperature Suzuki–Miyaura coupling reaction in aqueous media

Magnetic nanoparticles of Fe3O4 supported oxime palladacycle as a novel catalyst for room temperature Suzuki coupling reaction in aqueous media.

ChemInform Abstract: Polymer‐Supported Electron‐Rich Oxime Palladacycle as an Efficient Heterogeneous Catalyst for the Suzuki Coupling Reaction.

AbstractThe method is applied to the synthesis of a precursor of the drug valsartam.

Self-Supported Ligands as a Platform for Catalysis: Use of a Polymeric Oxime in a Recyclable Palladacycle Precatalyst for Suzuki–Miyaura Reactions

A self-supported oxime palladacycle precatalyst for ­Suzuki–Miyaura reactions was synthesized based on the polyether ether ketone architecture. This precatalyst was found to be highly efficient in Suzuki–Miyaura reactions when aryl bromides were used as substrates, but was less efficient in cross-coupling reactions when aryl chlorides were used. The polymeric palladacycle could be recovered and reused up to four times in such reactions, affording excellent yield of the desired product. The approach represents a novel strategy for generating such self-supported complexes for catalysis.

Polymer‐Supported Electron‐Rich Oxime Palladacycle as an Efficient Heterogeneous Catalyst for the Suzuki Coupling Reaction

AbstractVarious electron‐rich oxime palladacycle resins designed as heterogeneous catalysts were employed for the Suzuki coupling reaction of aryl halides with arylboronic acids. The electron‐richness of the oxime ligand was controlled by the substituted alkoxy groups. Evaluation based on the electronic effect of the catalysts revealed that the alkoxy‐substituted oxime palladacycle resins showed better catalytic activity than palladated Kaiser oxime resin in the Suzuki coupling reactions and that the catalytic activity of oxime palladacycle resins increased as the electron‐richness of oxime ligand increased. The most electron‐rich oxime palladacycle resin exhibited an excellent catalytic performance for the synthesis of both biaryl and heterobiaryl compounds, despite its heterogeneous system. As a practical application of the catalyst, a valsartan precursor was synthesized in high yield under mild conditions. The electron‐rich oxime resin could also be reused for up to 5 cycles while maintaining good catalytic activity in the Suzuki coupling reaction.magnified image

Microwave‐Promoted Copper‐Free Sonogashira–Hagihara Couplings of Aryl Imidazolylsulfonates in Water

AbstractAryl imidazol‐1‐ylsulfonates have been efficiently cross‐coupled with aryl‐, alkyl‐, and silylacetylenes in neat water under copper‐free conditions at 110 °C assisted by microwave irradiation. Using 0.5 mol% of an oxime palladacycle as precatalyst, 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (SPhos, 2 mol%) as ligand, hexadecyltrimethylammonium bromide (CTAB) as additive, and triethylamine (TEA) as base, a wide array of disubstituted alkynes has been prepared in good to high yields in only 30 min.

Microwave‐Promoted Suzuki–Miyaura Cross‐Coupling of Aryl Imidazolylsulfonates in Water

AbstractAryl imidazol‐1‐ylsulfonates are efficiently cross‐coupled with potassium aryl‐ and alkenyltrifluoroborates in neat water under microwave heating (40 W, 110 °C) using 0.5 mol% of oxime palladacycle 1a, hexadecyltrimethyl ammonium bromide (CTAB) as additive, and triethylamine as base. Under these simple phosphane‐free reaction conditions a wide array of biaryl, stilbene and styrene derivatives has been prepared in good to high yields and with high regio‐ and diastereoselectivities in only 30 min.

Fluorous Oxime Palladacycle: A Precatalyst for Carbon–Carbon Coupling Reactions in Aqueous and Organic Medium

To facilitate precatalyst recovery and reuse, we have developed a fluorous, oxime-based palladacycle 1 and demonstrated that it is a very efficient and versatile precatalyst for a wide range of carbon-carbon bond formation reactions (Suzuki-Miyaura, Sonogashira, Stille, Heck, Glaser-type, and Kumada) in either aqueous or organic medium under microwave irradiation. Palladacycle 1 could be recovered through F-SPE in various coupling reactions with recovery ranging from 84 to 95% for the first cycle. Inductively coupled plasma optical emission spectrometry (ICP-OES) analyses of the Pd content in the crude product from each class of transformation indicated extremely low levels of leaching and the palladacycle could be reused four to five times without significant loss of activity.

Microwave‐Promoted Palladium‐Catalysed Oxyarylation of Dihydronaphthalene and Chromenes by o‐Iodophenols and Its Acetates

AbstractThe oxyarylation of dihydronaphthalene (1a), two electron‐rich (1b,c) and one electron‐poor (2) chromenes with different o‐iodophenols and their acetates 3a–h has been investigated by using either Pd(OAc)2 (10 mol‐%) as precatalyst and Ag2CO3 as base in acetone as solvent or oxime palladacycle 5 as precatalyst and dicyclohexylamine as base in DMA/H2O. The reactions, which were strongly accelerated under microwave heating, afforded the best yields when electron‐rich chromenes reacted with o‐iodophenols substituted by electron‐withdrawing groups in the presence Pd(OAc)2 and Ag2CO3. However, in the case of electron‐poor chromenes the best yield was obtained with the electron‐rich o‐iodophenol 3g.

ChemInform Abstract: Efficient Suzuki—Miyaura Coupling of Deactivated Aryl Chlorides Catalyzed by an Oxime Palladacycle.

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