Silica‐Supported P2O5 as an Efficient Heterogeneous Catalyst for the One Pot Synthesis of 3‐Amino‐imidazo[2,1‐b](1,3)benzothiazole under Green Conditions

The new approach involving the solid supported catalyst for the formation of C–N bond followed by cyclization has been reported. In this work we have reported a facile, efficient, and environment‐friendly protocol for the synthesis of some new 3‐amino‐imidazo[2,1‐b](1,3)benzothiazole derivatives by one‐pot condensation of 2‐aminobenzothiazole, indole‐3‐carbaldehyde, and aryl isocyanide in the presence of silica‐supported P₂O₅ as a heterogeneous solid acid catalyst. The reaction was performed using conventional method under green conditions. The present approach offers the advantages of simple methodology, inexpensive acid catalyst, short reaction time, easy work up with excellent yield, simple purification and use of green solvent. All the newly synthesized compounds were characterized in details using physical and chemical techniques such as melting point, ¹H NMR, ¹³C NMR, and FTIR spectroscopy.     

Solid‐State NMR Characterization of Wilkinson’s Catalyst Immobilized in Mesoporous SBA‐3 Silica

The Wilkinson’s catalyst [RhCl(PPh₃)₃] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA‐3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid‐state NMR methods. The successful modification of the silica surface was confirmed by ²⁹Si CP‐MAS NMR experiments. The presence of the T_n peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. ³¹P‐³¹P J‐resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable ³¹P‐³¹P J‐coupling, well resolvable in 2D MAS NMR experiments. This J‐coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable ³¹P‐³¹P J‐coupling in off‐magic‐angle‐spinning experiments, as well as slow‐spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules.     

Solvent‐free and nonisocyanate melt transurethane reaction for aliphatic polyurethanes and mechanistic aspects

A novel melt transurethane polycondensation route for polyurethanes under solvent‐free and nonisocyanate condition was developed for soluble and thermally stable aliphatic or aromatic polyurethanes. The new transurethane process was investigated for A + B, A‐A + B, and A‐A + B‐B (A‐urethane and B‐hydroxyl) ‐type condensation reactions, and also monomers bearing primary and secondary urethane or hydroxyl functionalities. The transurethane process was confirmed by ¹H and ¹³C NMR, and molecular weight of the polymers were obtained as M_n = 10–15 × 10³ and M_w = 15–45 × 10³ g/mol. The mechanistic aspects of the melt transurethane process and role of the catalyst were investigated using model reactions, ¹H NMR, and MALDI‐TOF‐MS. The model reactions indicated the occurrence of 97% reaction in the presence of catalyst, whereas its absence gave only less than 2% of the product. The polymer samples were subjected for end‐group analysis using MALDI‐TOF‐MS, which confirms the Ti‐catalyst mediated nonisocyanate pathway in the melt transurethane process. Almost all the polyurethanes were stable up to 280 °C, and the T_g of the polyurethanes can be easily fine‐tuned from ?30 to 120 °C by using appropriate diols in the melt transurethane process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2445–2458, 2008     

Synthesis and characterization of a novel soluble reactive ladder‐like polysilsesquioxane with side‐chain 2‐(4‐chloromethyl phenyl) ethyl groups

A new kind of soluble structure‐ordered ladder‐like polysilsesquioxane with reactive side‐chain 2‐(4‐chloromethyl phenyl) ethyl groups ( L ) was first synthesized by stepwise coupling polymerization. The monomer, 2‐(4‐chloromethyl phenyl) ethyltrichlorosilane ( M ), was synthesized successfully by hydrosilylation reaction with dicyclopentadienylplatinum(II) chloride (Cp₂PtCl₂) ­catalyst. Monomer and polymer structures were characterized by FT‐IR, ¹H‐NMR, ¹³C‐NMR, ²⁹Si‐NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO) and X‐ray diffraction (XRD). This novel reactive ladder‐like polymer has promise potential applications as initiator for atom transfer radical polymerization, and as precursor for a variety of advanced functional polymers. Copyright © 2001 John Wiley & Sons, Ltd.     

Rhodium‐catalysed hydroformylation of 1‐octene using aryl and ferrocenyl Schiff base‐derived ligands

Monometallic and heterobimetallic complexes of Rh(I) bearing chelating N ,O ‐bidentate aryl‐ and ferrocenyl‐derived ligands have been synthesised via Schiff base condensation reactions, and characterised fully using ¹H NMR, ¹³C{¹H} NMR and Fourier transform infrared spectroscopies, elemental analysis and mass spectrometry. The new monometallic and heterobimetallic complexes were evaluated as potential catalyst precursors in the hydroformylation of 1‐octene at 95°C and 40 bar. The ferrocenylimine mononuclear compounds were inactive in the hydroformylation experiments. The Rh(I) monometallic and the ferrocene–Rh(I) heterobimetallic pre‐catalysts displayed good activity and conversion of 1‐octene as well as outstanding chemoselectivity towards aldehydes in the hydroformylation reaction.     

Inorganic–organic hybrid chitosan‐based Schiff base–Ni complex as a novel,highly efficient and recyclable heterogeneous catalyst for synthesis of pyrazolophthalazinediones

A Schiff base based on chitosan was synthesized through treatment of chitosan and p ‐dimethylaminobenzaldehyde in methanol solution. This biopolymeric Schiff base was used to prepare a new first row transition metal complex of Ni(II). The biopolymeric Schiff base and the synthesized tetra‐coordinated complex were characterized using Fourier transform infrared, ¹H NMR and ¹³C NMR techniques. Then, an efficient synthetic method for functionalized 1H –pyrazolo[1,2‐b ]phthalazine‐5,10‐diones was successfully developed using one‐pot domino reaction of ninhydrin and malononitrile with 3‐arylamino‐5,5‐dimethyl‐2‐cyclohexenones catalysed by the chitosan‐based Schiff base complex of Ni(II) at room temperature. The advantages of this protocol are easy work‐up, short reaction times and high yield of products and also the catalyst can be readily isolated from the reaction mixture and recycled without loss of catalytic activity.     

Multicomponent Approach Towards the Synthesis of Substituted Pyrroles under Supramolecular Catalysis Using β‐Cyclodextrin as a Catalyst in Water Under Neutral Conditions

Synthesis of substituted pyrroles in H₂O by using β‐cyclodextrin as a supramolecular catalyst is described. This reaction has several advantages over existing methods and provides substituted pyrroles in good‐to‐excellent yields (79–89%). The supramolecular catalysis of the reaction was studied using ¹H‐NMR spectroscopy. β‐Cyclodextrin can be recovered and reused several times without loss of activity.     

Efficient and Facile Catalyst‐free One‐Pot Synthesis and Characterization of Some Novel Bis(2‐benzothiazole) Derivatives

A general method for preparation of benzothiazole derivatives including oxidative cyclization of the corresponding Schiff bases was reported. Herein, we have been synthesized a series of new acyclic‐substituted bis(2‐arylbenzothiazoles). Synthesis of analogs substituted in the benzothiazole ring was achieved via the direct condensation reaction of o‐aminothiophenol with some of dialdehyde compounds under catalyst free in high yields. The structure of these products has been fully characterized by physical and spectroscopic data such as IR, ¹H‐NMR, ¹³C‐NMR, UV‐Vis, MS, and CHN analysis.     

Polysiloxane microspheres functionalized with imidazole groups as a palladium catalyst support

Polysiloxane microspheres containing a large number of silanol groups were obtained by an emulsion process of modified polyhydromethylsiloxane. N‐substituted imidazole groups were grafted on these microspheres by the silylation of their silanol groups with N‐[γ‐(dimethylchlorosilyl)propyl]imidazole hydrochloride. The progress of the reaction was monitored using ²⁹Si and ¹³C magic angle spinning (MAS) NMR and its impact on microsphere morphology was studied using scanning electron microscopy (SEM). The usefulness of the imidazole‐functionalized microspheres as a support for a metal catalyst was demonstrated by their reaction with PdCl₂(PhCN)₂. In this way a new heterogenized catalyst, Pd(II) complex with imidazole ligands supported on polysiloxane microspheres, was generated. This catalyst, MPd , was characterized using ¹³C and ²⁹Si MAS NMR, X‐ray photoelectron, Fourier transform infrared and far‐infrared spectroscopies, X‐ray diffraction, SEM–energy‐dispersive X‐ray spectroscopy and wide‐angle X‐ray scattering. The catalyst appears in two structures, as Pd(II) complex and Pd(0) nanoclusters. Its catalytic activity was tested using a model reaction, the hydrogenation of cinnamaldehyde, and compared with that of an analogous complex operating in a homogeneous system. MPd showed a high activity in the promotion of hydrogenation of cinnamaldehyde. The activity in the substrate conversion was stable at least in five cycles of this reaction. The main product was hydrocinnamaldehyde which could be obtained with a yield above 70%. A mechanism of the reaction is proposed. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of New 1,2,3‐Triazole Derivatives Possessing 4H‐Pyran‐4‐one Moiety by 1,3‐Dipolar Cycloaddition Reaction of Azidomethyl Phenylpyrone with Various Alkynes

A series of new 1,2,3‐triazole derivatives were synthesized by 1,3‐dipolar cycloaddition reaction of 2‐(4‐azidomethylphenyl)‐6‐phenyl‐4H‐pyran‐4‐one with different alkynes in 40–71% yields. In the case of terminal alkynes, the reaction was proceeded in the presence of Cu(I) catalyst. The structure of the synthesized compounds were confirmed by FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopy and elemental analysis.     

Synthesis of New Imino Containing Tetrahydrochromeno[2,3‐d]pyrimidines

Some new derivatives of 3,5‐diaryl‐4‐imino‐5,7,8,9‐tetrahydro‐3H‐chromeno[2,3‐d ]pyrimidine have been prepared through a condensation reaction of 2‐amino‐4‐aryl‐3‐cyano‐5,6,7,8‐tetrahydrobenzo[b ]pyrans with triethyl orthoformate in boiling acetic anhydride followed by cyclization with primary aryl amines in the presence of a few drops triethylamine as catalyst in refluxing ethanol. The products were characterized on the basis of IR, ¹H‐NMR, and ¹³C‐NMR spectral and microanalytical data.     

Synthesis,characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1‐octene, cyclooctene, (S )‐limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS‐ATC‐[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S )‐limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.     

Natural Abundance 15N NMR by Dynamic Nuclear Polarization: Fast Analysis of Binding Sites of a Novel Amine‐Carboxyl‐Linked Immobilized Dirhodium Catalyst

A novel heterogeneous dirhodium catalyst has been synthesized. This stable catalyst is constructed from dirhodium acetate dimer (Rh₂(OAc)₄) units, which are covalently linked to amine‐ and carboxyl‐bifunctionalized mesoporous silica (SBA‐15?NH₂?COOH). It shows good efficiency in catalyzing the cyclopropanation reaction of styrene and ethyl diazoacetate (EDA) forming cis‐ and trans‐1‐ethoxycarbonyl‐2‐phenylcyclopropane. To characterize the structure of this catalyst and to confirm the successful immobilization, heteronuclear solid‐state NMR experiments have been performed. The high application potential of dynamic nuclear polarization (DNP) NMR for the analysis of binding sites in this novel catalyst is demonstrated. Signal‐enhanced ¹³C CP MAS and ¹⁵N CP MAS techniques have been employed to detect different carboxyl and amine binding sites in natural abundance on a fast time scale. The interpretation of the experimental chemical shift values for different binding sites has been corroborated by quantum chemical calculations on dirhodium model complexes.     

Ru–bis(pyridine)pyrazolate (bpp)‐Based Water‐Oxidation Catalysts Anchored on TiO2: The Importance of the Nature and Position of the Anchoring Group

Three distinct functionalisation strategies have been applied to the in,in‐[{Ru^II(trpy)}₂(μ‐bpp)(H₂O)₂]³⁺ (trpy=2,2′:6′,2′′‐terpyridine, bpp=bis(pyridine)pyrazolate) water‐oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphonate anchoring groups to the terpyridine and bis(pyridyl)pyrazolate ligands. The complexes were characterised in solution by using 1D NMR, 2D NMR, and UV/Vis spectroscopic analysis and electrochemical techniques. The complexes were then anchored on TiO₂‐coated fluorinated tin oxide (FTO) films, and the reactivity of these new materials as water‐oxidation catalysts was tested electrochemically through controlled‐potential electrolysis (CPE) with oxygen evolution detected by headspace analysis with a Clark electrode. The results obtained highlight the importance of the catalyst orientation with respect to the titania surface in regard to its capacity to catalytically oxidize water to dioxygen.     

Synthesis of Ethyl 2‐Amino‐4‐benzoyl‐5‐oxo‐5,6‐dihydro‐4H‐pyrano[3,2‐c]quinoline‐3‐carboxylates by a One‐pot,Three‐Component Reaction in the Presence of TPAB

In this research, in order to synthesize a series of ethyl 2‐amino‐4‐benzoyl‐5‐oxo‐5,6‐dihydro‐4H‐pyrano[3,2‐c]quinoline‐3‐carboxylates, a green and an efficient method is proposed through one‐pot three‐component reaction of substituted arylglyoxals, ethyl cyanoacetate, and 4‐hydroxyquinolin‐2(1H)‐one in the presence of terapropylammonium bromide as a catalyst in good yields. All synthesized new substances were characterized by FTIR, ¹H‐NMR, and ¹³C‐NMR spectral data and elemental analysis.     

Transfer hydrogenation of ketones catalysed by half‐sandwich (η6‐p‐cymene) ruthenium(II) complexes incorporating benzoylhydrazone ligands

Neutral half‐sandwich η⁶‐p ‐cymene ruthenium(II) complexes of general formula [Ru(η⁶‐p ‐cymene)Cl(L)] (HL = monobasic O, N bidendate benzoylhydrazone ligand) have been synthesized from the reaction of [Ru(η⁶‐p ‐cymene)(μ‐Cl)Cl]₂ with acetophenone benzoylhydrazone ligands. All the complexes have been characterized using analytical and spectroscopic (Fourier transform infrared, UV–visible, ¹H NMR, ¹³C NMR) techniques. The molecular structures of three of the complexes have been determined using single‐crystal X‐ray diffraction, indicating a pseudo‐octahedral geometry around the ruthenium(II) ion. All the ruthenium(II) arene complexes were explored as catalysts for transfer hydrogenation of a wide range of aromatic, cyclic and aliphatic ketones with 2‐propanol using 0.1 mol% catalyst loading, and conversions of up to 100% were obtained. Further, the influence of other variables on the transfer hydrogenation reaction, such as base, temperature, catalyst loading and substrate scope, was also investigated.     

Synthesis,Solid‐State NMR Characterization,and Application for Hydrogenation Reactions of a Novel Wilkinson’s‐Type Immobilized Catalyst

Silica nanoparticles (SiNPs) were chosen as a solid support material for the immobilization of a new Wilkinson’s‐type catalyst. In a first step, polymer molecules (poly(triphenylphosphine)ethylene (PTPPE); 4‐diphenylphosphine styrene as monomer) were grafted onto the silica nanoparticles by surface‐initiated photoinferter‐mediated polymerization (SI‐PIMP). The catalyst was then created by binding rhodium (Rh) to the polymer side chains, with RhCl₃ ? x H₂O as a precursor. The triphenylphosphine units and rhodium as Rh^I provide an environment to form Wilkinson’s catalyst‐like structures. Employing multinuclear (³¹P, ²⁹Si, and ¹³C) solid‐state NMR spectroscopy (SSNMR), the structure of the catalyst bound to the polymer and the intermediates of the grafting reaction have been characterized. Finally, first applications of this catalyst in hydrogenation reactions employing para‐enriched hydrogen gas (PHIP experiments) and an assessment of its leaching properties are presented.     

Calix[n]arenes mediated phase‐transfer catalytic synthesis of purine derivatives

A new route was designed to achieve the synthesis of purine derivatives under phase‐transfer catalysis conditions using calix[n]arenes TAC_nA (n = 4, 6, and 8) as phase‐transfer catalyst for the first time in this particular type of synthesis. The compounds were synthesized in excellent yields (70%–80%) and the structures were established on the basis of consistent IR, ¹H NMR, FAB‐Mass, and elemental analyses data. Their purity has been ascertained by chromatographic resolution using acetonitrile, methanol, and water (50:30:20, v/v) as eluenting system. Moreover, the kinetics of the reaction was studied and it was found to obey first‐order kinetics. Effect of various parameters, namely, temperature, amount of catalyst, stirring speed, and so on was also investigated. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 265–274, 2009     

A novel and versatile potassium‐based catalyst for the ring opening polymerization of cyclic esters

Poly(lactide) (PLA), poly(ε‐caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) homopolymers of high molecular weight were prepared using potassium‐based catalyst. Polymerizations were carried out in toluene at room temperature. The chemical structure of the polymers was investigated by ¹H and ¹³C NMR. The physical properties investigated by GPC and DSC for the polymers obtained are similar to those prepared using tin octanoate based catalyst. Using a sequential polymerization procedure, PLA‐b‐PCL, PLA‐b‐PTMC, and PCL‐b‐PTMC diblock copolymers were synthesized and characterized in terms of their composition and physical properties. The formation of diblock copolymers was confirmed by NMR and DSC measurements. In vitro cytotoxicity tests have been carried out using MTS assay and the results show the biocompatibility of these polymers in the presence of the fibroblast cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5348–5362, 2008     

Synthesis of a new iron–sulfur cluster compound and its photocatalytic H2 evolution activity through visible light irradiation

A new iron–sulfur cluster compound, namely [(μ‐BNT)Fe₂(CO)₆] ( A ; BNT = (R)‐1,1′‐binaphthalene‐2,2′‐dithiol), was synthesized by self‐assembly of BNT with [Fe₃(CO)₁₂] and characterized using ¹H NMR, ¹³C NMR, infrared spectra and elemental analysis. The H₂ evolution activity of A was evaluated in a constructed homogeneous photocatalytic system by combining A as catalyst, xanthene dyes as photosensitizer and triethylamine as sacrificial reagent, to give efficient H₂ generation under visible‐light irradiation (λ > 420 nm). The maximum H₂ evolution of 404 turnovers (versus catalyst) was recorded under optimal conditions in CH₃CN–H₂O (1:1, v/v) after 4 h irradiation. The mechanism of H₂ evolution is briefly discussed using fluorescence spectra and electrochemical analysis. Copyright © 2016 John Wiley & Sons, Ltd.