Dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe3O4@SiO2 nanoparticles as a novel recyclable catalyst for N‐arylation of nitrogen heterocycles and green synthesis of 5‐substituted 1H‐tetrazoles

In this study, dendrimer‐encapsulated Cu(Π) nanoparticles immobilized on superparamagnetic Fe₃O₄@SiO₂ nanoparticles were prepared via a multistep‐synthesis. Then, the synthesized composite was fully characterized by various techniques such as fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), dynamic light scattering (DLS), UV‐vis spectroscopy, energy dispersive X‐ray analysis (EDX), thermogravimetric analysis (TGA) and vibration sample magnetometer (VSM). From the information gained by FE‐SEM and TEM studies it can be inferred that the particles are mostly spherical in shape and have an average size of 50 nm. Also, the amount of Cu is determined to be 0.51 mmol/g in the catalyst by inductively coupled plasma (ICP) analyzer. This magnetic nano‐compound has been successfully applied as a highly efficient, magnetically recoverable and stable catalyst for N‐arylation of nitrogen heterocycles with aryl halides (I, Br) and arylboronic acids without using external ligands or additives. The catalyst was also employed in a one‐pot, three‐component reaction for the efficient and green synthesis of 5‐substituted 1H‐tetrazoles using various aldehydes, hydroxylamine hydrochloride and sodium azide in water. The magnetic catalyst can be easily separated by an external magnet bar and is recycled seven times without significant loss of its activity.     

Synthesis and characterization of copper(II) Schiff base complex supported on Fe3O4 magnetic nanoparticles: a recyclable catalyst for the one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones

Fe₃O₄–Schiff base of Cu(II) is found to be a recyclable and heterogeneous catalyst for the rapid and efficient synthesis of various 2,3‐dihydroquinazolin‐4(1H)‐one derivatives from the two‐component condensation of 2‐aminobenzamide and an aldehyde. This reaction is simple, green and cost‐effective. Separation and recycling can also be easily done by magnetic decantation of the Fe₃O₄ nanoparticles with an external magnet. The prepared catalyst was characterized using thermogravimetry, Fourier transform infrared spectroscopy, vibrating sample magnetometry, inductively coupled plasma analysis, X‐ray diffraction and scanning electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly efficient and reusable polystyrene‐supported copper(II) catalytic system for S‐arylation of potassium thiocyanate by aryl halides in water

An inexpensive, efficient and environmentally friendly copper(II) catalyst supported on polystyrene was successfully synthesized and used as a heterogeneous catalyst for S‐arylation of potassium thiocyanate by aryl halides. Also this catalyst could be recovered and reused several times without any noticeable decrease in its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Fe3O4‐supported Schiff‐base copper (II) complex: A valuable heterogeneous nanocatalyst for one‐pot synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives

A novel Cu (II) Schiff‐base complex immobilized on core‐shell magnetic Fe₃O₄ nanoparticles (Fe₃O₄@SPNC) was successfully designed and synthesized. The structural features of these nanoparticles were studied and confirmed by using various techniques including FT‐IR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), vibrating sample magnetometer (VSM), X‐Ray diffraction (XRD), wavelength dispersive X‐ray spectroscopy (WDX), and inductively coupled plasma (ICP). These newly synthesized nanoparticles have been used as efficient heterogeneous catalytic system for one‐pot multicomponent synthesis of new pyrano[2,3‐b]pyridine‐3‐carboxamide derivatives. Notably, the catalyst could be easily separated from the reaction mixture by using an external magnet and reused for several successive reaction runs with no significant loss of activity or copper leaching. The present protocol benefits from a hitherto unreported MNPs‐immobilized Cu (II) Schiff‐base complex as an efficient nanocatalyst for the synthesis of newly reported derivatives of pyrano[2,3‐b]pyridine‐3‐carboxamide from one‐pot multicomponent reactions.     

Cu(II) Schiff base complex supported on Fe3O4 nanoparticles as an efficient nanocatalyst for the selective aerobic oxidation of alcohols

Herein, we have prepared a new Cu(II) Schiff base complex supported onto the surface of modified Fe₃O₄ nanoparticles as highly stable, heterogeneous and magnetically recyclable nanocatalyst for the selective aerobic oxidation of different alcohols. The structure, morphology, chemical composition and magnetic property of the nanocatalyst and its precursors were characterized using FT‐IR, TGA, AAS, ICP‐AES, XRD, SEM, EDS, VSM and N₂ adsorption–desorption analyses. Characterization results exhibited the uniform spherical morphology for nanocatalyst and its precursors. A promising eco‐friendly method with short reaction time and high conversion and selectivity for oxidation of various primary and secondary alcohols under O₂ atmosphere condition was achieved. The synthesized nanocatalyst could be recovered easily by applying an external magnetic field and reused for least eight subsequent reaction cycles with only negligible deterioration in catalytic performance.     

A New Route to N‐Aryl 2‐Alkenamides,N‐Allyl N‐Aryl 2‐Alkenamides,and N‐Aryl α,β‐Unsaturated γ‐Lactams from N‐Aryl 3‐(Phenylsulfonyl)propanamides

A series of N‐aryl 2‐alkenamides were produced efficiently by treating N‐aryl 3‐(phenylsulfonyl)‐propanamides with potassium tert‐butoxide in THF at 0°C. With out isolation, it was further treated with an additional equivalent of potassium tert‐butoxide and allyl bromide to give N‐allyl N‐aryl 2‐alkenamides in one pot in good yields. Followed by a ring‐closing metathesis reaction, these N‐allyl N‐aryl 2‐alkenamides were respectively converted into corresponding N‐aryl α,β‐unsaturated γ‐lactams in moderate yields.     

Multi‐wall carbon nanotube supported Co (II) Schiff base complex: an efficient and highly reusable catalyst for synthesis of 1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b]pyran derivatives

An immobilized Co (II) Schiff base complex supported on multi‐wall carbon nanotubes was synthesized and characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy , thermogravimetric analysis and inductively coupled plasma mass spectrometry. It was shown that the supported complex is a facile, eco‐friendly, recyclable, reusable and green catalyst for three‐component condensation of 2‐naphthol and acetamide with various aldehydes for the synthesis of 1‐amidoalkyl‐2‐naphthol derivatives under solvent‐free conditions. Also, in a further study, the catalytic application was studied in the synthesis of tetrahydrobenzo[b ]pyran derivatives via the condensation reaction of malononitrile and dimedone with several aromatic aldehydes. The procedures suggested here for the synthesis of 1‐amidoalkyl‐2‐naphthol and tetrahydrobenzo[b ]pyran derivatives offer several advantages, such as stability, recyclability and eco‐friendliness of the catalyst, simple experimental conditions, short reaction times, high to excellent yields and easy work‐up.     

Phosphoryl group differentiating α‐amino acids from β‐ and γ‐amino acids in prebiotic peptide formation

In recent years β‐amino acids have increased their importance enormously in defining secondary structures of β‐peptides. Interest in β‐amino acids raises the question: Why and how did nature choose α‐amino acids for the central role in life? In this article we present experimental results of MS and ³¹P NMR methods on the chemical behavior of N‐phosphorylated α‐alanine, β‐alanine, and γ‐amino butyric acid in different solvents. N‐Phosphoryl α‐alanine can self‐assemble to N‐phosphopeptides either in water or in organic solvents, while no assembly was observed for β‐ or γ‐amino acids. An intramolecular carboxylic–phosphoric mixed anhydride (IMCPA) is the key structure responsible for their chemical behaviors. Relative energies and solvent effects of three isomers of IMCPA derived from α‐alanine (2a–c), with five‐membered ring, and five isomers of IMCPA derived from β‐alanine (4a–e), with six‐membered ring, were calculated with density functional theory at the B3LYP/6‐31G** level. The lower relative energy (3.2 kcal/mol in water) of 2b and lower energy barrier for its formation (16.7 kcal/mol in water) are responsible for the peptide formation from N‐phosphoryl α‐alanine. Both experimental and theoretical studies indicate that the structural difference among α‐, β‐, and γ‐amino acids can be recognized by formation of IMCPA after N‐phosphorylation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 232–241, 2003     

Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica‐coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α‐methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n ‐butanol) using tert ‐butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂‐Schiff base‐Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst     

Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe2O3@TiO2 (γ‐Fe2O3@TiO2‐EG‐Cu(II)): A highly efficient magnetically separable heterogeneous nanocatalyst for one‐pot synthesis of highly substituted imidazoles

A simple, efficient and eco‐friendly procedure has been developed using Cu(II) immobilized on guanidinated epibromohydrin‐functionalized γ‐Fe₂O₃@TiO₂ (γ‐Fe₂O₃@TiO₂‐EG‐Cu(II)) for the synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles, via the condensation reactions of various aldehydes with benzil and ammonium acetate or ammonium acetate and amines, under solvent‐free conditions. High‐resolution transmission electron microscopy analysis of this catalyst clearly affirmed the formation of a γ‐Fe₂O₃ core and a TiO₂ shell, with mean sizes of about 10–20 and 5–10 nm, respectively. These data were in very good agreement with X‐ray crystallographic measurements (13 and 7 nm). Moreover, magnetization measurements revealed that both γ‐Fe₂O₃@TiO₂ and γ‐Fe₂O₃@TiO₂‐EG‐Cu(II) had superparamagnetic behaviour with saturation magnetization of 23.79 and 22.12 emu g^?1, respectively. γ‐Fe₂O₃@TiO₂‐EG‐Cu(II) was found to be a green and highly efficient nanocatalyst, which could be easily handled, recovered and reused several times without significant loss of its activity. The scope of the presented methodology is quite broad; a variety of aldehydes as well as amines have been shown to be viable substrates. A mechanism for the cyclocondensation reaction has also been proposed.     

NH2SO3H–SiO2 as a new water‐compatible,recyclable heterogeneous catalyst for the synthesis of novel (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction

NH₂SO₃H–SiO₂/water as a novel catalytic system was used for the synthesis of (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction at reflux conditions. The methodology was of general applicability and the catalyst exhibited activity up to five cycles. The catalyst was characterized for the first time using FT‐IR, X‐ray diffraction and scanning electron microscopic–energy dispersion analytical X‐ray. The stability of the catalyst was evaluated by differential scanning calorimetry and TGA/differential thermal analysis. High efficiency of the catalyst along with its recycling ability and the rather low loading demonstrated in reactions are the merits of the presented protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

Palladium‐catalyzed carbonylative cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with primary amines leading to N‐alkylmaleimides

Cyclic β‐bromo‐α,β‐unsaturated carboxylic acids are carbonylatively cyclized with primary amines under carbon monoxide pressure in MeCN in the presence of a catalytic amount of PdCl₂(PPh₃)₂ to give N‐alkylmaleimides. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel water soluble bis(μ‐chloro) bridged Cu(II) binuclear and mononuclear complexes: Synthesis,characterization and biological evaluation

A water soluble chloro bridged binuclear copper(II) complex (3) and mononuclear complex (4) have been synthesized from chloro substituted 2‐oxo‐1,2‐dihydroquinolin‐3‐yl‐methylene‐2 hydroxybenzohydrazide 1 and 2 and CuCl₂·2H₂O. The structures of the complexes have been determined by single crystal X‐ray diffraction. The binding interactions of the ligands and complexes with CT‐DNA and protein have been evaluated by absorption and emission spectroscopic method. CT‐DNA and ethidium bromide (EB) competitive studies revealed that the compounds could interact with CT‐DNA through intercalation binding mode. Interactions of the compounds with BSA were also studied by UV−visible, fluorescence and synchronous fluorescence spectroscopic methods which showed that the compounds had a strong binding affinity with BSA through static quenching process. The cytotoxic effect of the compounds examined on cancer cell lines, such as A549 (lung cancer) and MCF7 (breast cancer) cell lines showed that all four compounds exhibited substantial cytotoxic activity.     

Investigation of pharmacophore and antipharmacophore features of certain dimethyltin(IV) complexes of flexible N‐protected amino acids and fluorinated β‐diketone/β‐diketones

A set of pentacoordinated dimethyltin(IV) complexes of flexible N‐protected amino acids and fluorinated β‐diketone/β‐diketones was screened for their antibacterial activity against Pseudomonas aeruginosa , Staphylococcus aureus and Streptomyces griseus . These pentacoordinated complexes of the type Me₂SnAB (where : R = CH(CH₃)C₂H₅, A₁H; CH₂CH(CH₃)₂, A₂H; CH(CH₃)₂, A₃H; CH₂C₆H₅, A₄H; and BH = R'C(O)CH₂C(O)R″: R′ = C₆H₅, R″ = CF₃, B₁H; R′ = R″ = CH₃, B₂H; R′ = C₆H₅, R″ = CH₃, B₃H; R′ = R″ = C₆H₅, B₄H) were generated by the reactions of dimethyltin(IV) dichloride with sodium salts of flexible N‐protected amino acids (ANa) and fluorinated β‐diketone/β‐diketones (BNa) in 1:1:1 molar ratio in refluxing dry benzene solution. Plausible structures of these complexes were elucidated on the basis of physicochemical and spectral studies. ¹¹⁹Sn NMR spectral data revealed the presence of pentacoordinated tin centres in these dimethyltin(IV) complexes.     

Hydroxyl‐tolerated polymerization of N‐phenoxycarbonyl α‐amino acids: A simple way to polypeptides bearing hydroxyl groups

Differing from the moisture‐sensitive α‐amino acid N‐carboxyanhydrides (AA‐NCAs) monomers, N‐phenoxycarbonyl α‐amino acids (AA‐NPCs) can be prepared and stored in open air. In this contribution, we report that the controlled polymerizations of AA‐NPC monomers of O‐tert‐butyl‐dl ‐serine (BRS‐NPC), N^ε‐benzyloxycarbonyl‐l ‐lysine (ZLL‐NPC) and N^ε‐trifluoroacetyl‐l ‐lysine (FLL‐NPC) initiated by amines are surprisingly able to tolerate common nucleophilic impurities such as water and alcohols at a level of monomer concentration. The structures of polypeptides synthesized in the presence of water or alcohols agree well with the designed ones in the case of repeated chain extensions. Detailed mechanism study and density functional theory calculation reveal that the low concentration of AA‐NCA and the high activity of amines are the key factors to the controllability of AA‐NPC polymerizations. The water‐ and alcohol‐tolerant property in polymerizations of AA‐NPCs encourages the following studies on unprotected (phenolic) hydroxyl groups containing AA‐NPCs. The controllable polymerizations of N‐phenoxycarbonyl l ‐tyrosine (LT‐NPC) and N‐phenoxycarbonyl S‐(3‐hydroxypropyl)‐l ‐cysteine (HLC‐NPC) initiated by amines are confirmed and reported for the first time, which extends the library of AA‐NPCs and polypeptides as well. All the universality of library, the convenience of monomer preparation, and the controllability and water‐ and alcohol‐tolerant property of polymerization of AA‐NPCs significantly enhance the feasibility of polypeptide synthesis, making AA‐NPC approach a promising synthetic method of polypeptides. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 907–916     

Synthesis,characterization and biological activity of diphenyltin(IV) complexes of N‐(3,5‐dibromosalicylidene)‐α‐amino acid and their diphenyltin dichloride adducts

Diphenyltin(IV) complexes of N‐(3,5‐dibromosalicylidene)‐α‐amino acid, Ph₂Sn[3,5‐Br₂‐2‐OC₆H₂ CH?NCH(R)COO] (where R = H, Me, i‐Pr, Bz), and their 1:1 adducts with diphenyltin dichloride, Ph₂Sn[3,5‐Br₂‐2‐OC₆H₂CH?NCH(R)COO]·Ph₂SnCl₂, have been synthesized and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. The crystal structure of Ph₂Sn[3,5‐Br₂‐2‐OC₆H₂CH?NCH(i‐Pr)COO] shows a distorted trigonal bipyramidal geometry with the axial locations occupied by a carboxylate–oxygen and a phenolic–oxygen atom of the ligand, and that of Ph₂Sn[3,5‐Br₂‐2‐OC₆H₂CH?NCH(i‐Pr)COO]·Ph₂SnCl₂ reveals that the two tin atoms are joined via the carbonyl atom of the ligand to form a mixed organotin binuclear complex. Bioassay indicates that the compounds possess better cytotoxic activity against three human tumor cell lines (HeLa, CoLo205 and MCF‐7) than cis‐platin and moderate antibacterial activity against two bacteria (E. coli and S. aureus). Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis and crystal structure of the dinuclear copper(II) Schiff base complex μ‐hydroxido‐μ‐chlorido‐bis{[bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine]chloridocopper(II)} dichloromethane sesquisolvate

Transition metal complexes of Schiff base ligands have been shown to have particular application in catalysis and magnetism. The chemistry of copper complexes is of interest owing to their importance in biological and industrial processes. The reaction of copper(I) chloride with the bidentate Schiff base N,N′‐bis(trans‐2‐nitrocinnamaldehyde)ethylenediamine {Nca₂en, systematic name: (1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]} in a 1:1 molar ratio in dichloromethane without exclusion of air or moisture resulted in the formation of the title complex μ‐chlorido‐μ‐hydroxido‐bis(chlorido{(1E,1′E,2E,2′E)‐N,N′‐(ethane‐1,2‐diyl)bis[3‐(2‐nitrophenyl)prop‐2‐en‐1‐imine]‐κ²N,N′}copper(II)) dichloromethane sesquisolvate, [Cu₂Cl₃(OH)(C₂₀H₁₈N₄O₄)₂]·1.5CH₂Cl₂. The dinuclear complex has a folded four‐membered ring in an unsymmetrical Cu₂OCl₃ core in which the approximate trigonal bipyramidal coordination displays different angular distortions in the equatorial planes of the two Cu^II atoms; the chloride bridge is asymmetric, but the hydroxide bridge is symmetric. The chelate rings of the two Nca₂en ligands have different conformations, leading to a more marked bowing of one of the ligands compared with the other. This is the first reported dinuclear complex, and the first five‐coordinate complex, of the Nca₂en Schiff base ligand. Molecules of the dimer are associated in pairs by ring‐stacking interactions supported by C—H…Cl interactions with solvent molecules; a further ring‐stacking interaction exists between the two Schiff base ligands of each molecule.