Bifunctional cobalt Salen complex: a highly selective catalyst for the coupling of CO2 and epoxides under mild conditions

A bifunctional cobalt Salen complex containing a Lewis acid metal center and two covalent bonded Lewis bases on the ligand was designed and used for the coupling of CO₂ and epoxides under mild conditions. The complex exhibited excellent activity (turnover frequency = 673/h) and selectivity (no less than 97%) for polymer formation in the copolymerization of propylene oxide (PO) and CO₂ at an appropriate combination of all variables. High molecular weight of 110 200 and yield 99% were achieved at a higher [PO]/[complex] ratio of 6000:1. The complex also worked satisfactorily for the terpolymerization of CO₂, PO and cyclohexene oxide (CHO), without formation of cyclic carbonate or ether linkages to give the polycarbonate. High cyclohexene carbonate unit content in the CO₂/PO/CHO terpolymers resulted in enhanced thermal stability. Copyright © 2011 John Wiley & Sons, Ltd.     

SnCl4-organic base: Highly efficient catalyst system for coupling reaction of CO2 and epoxides

A simple and highly efficient catalyst system of SnCl₄-organic base was developed to catalyze the coupling reaction of carbon dioxide and epoxides in very mild condition to yield the cyclic carbonates. The proposed mechanism was described in terms of in situ ¹¹⁹Sn NMR investigations.     

An efficient catalyst for Suzuki-Miyaura coupling reaction in aqueous medium under aerobic conditions

A cylcopalladated complex, [Pd(Cl)(k²N,C-CH₂C₆H₂(Me)₂CHNC₆H₃(Prⁱ)₂]₂ was found to be an excellent catalyst for Suzuki-Miyaura coupling of aryl halides with arylboronic acid in aqueous medium under aerobic conditions.     

Highly active, hexabutylguanidinium salt/zinc bromide binary catalyst for the coupling reaction of carbon dioxide and epoxides

An experimentally simple and inexpensive catalyst system based on hexabutylguanidinium/ZnBr₂ has been developed for the coupling of carbon dioxide and epoxides to form cyclic carbonates with significant catalytic activity under mild reaction conditions without using additional organic solvents (e.g. the turnover frequencies (TOF, h⁻¹) values as high as 6.6 × 10³ h⁻¹ for styrene oxide and 1.01 × 10⁴ h⁻¹ for epichlorohydrin). This catalyst system also offers the advantages of recyclability and reusability. Therefore, it is a very effective, environmentally benign, and simple catalytic process. The special steric and electrophilic characteristics of hexabutylguanidinium bromide ionic liquid result in the prominent performance of this novel catalyst system.     

Lithium trifluoromethanesulfonate (LiOTf) as a recyclable catalyst for highly efficient acetylation of alcohols and diacetylation of aldehydes under mild and neutral reaction conditions

A variety of alcohols and aldehydes were reacted with acetic anhydride at room temperature in the presence of a catalytic amount of lithium triflate (LiOTf) to produce the corresponding esters and 1,1-diacetates, respectively, in good to excellent yields under essentially neutral reaction conditions. Sensitive functional groups such as PhCO(2)-, OMe, and OTBDMS ethers survived intact under the described reaction conditions.     

Tetrabutylammonium bromide promoted efficient and chemoselective trimethylsilylation of primary and secondary alcohols under mild reaction conditions

A mild and efficient method for trimethylsilylation of alcohols with hexamethyldisilazane (HMDS) catalyzed by tetrabutylammonium bromide is reported. The method is highly chemoselective for the o-protection of primary and secondary alcohols in the presence of amines, thiols and tertiary alcohols.     

Phenylboronic acid as a mild and efficient catalyst for Biginelli reaction

The synthesis of 3,4-dihydropyrimidinone derivatives was achieved in good to excellent yields using phenylboronic acid as catalyst to promote the Biginelli three-component condensation of a diversity of aromatic aldehydes, ethyl acetoacetate and urea or thiourea.     

C2-symmetric bisprolinamide as a highly efficient catalyst for direct aldol reaction

[reaction: see text] The catalytic activity of the prolinamide-type catalysts may be improved by introducing additional prolinamide moiety into the catalyst, while the enantioselectivity can still be maintained or further improved. A C2-symmetric bisprolinamide with two prolinamide moieties has been found to be an excellent catalyst for direct aldol reaction with more than doubled reactivity and better asymmetric induction than its monoprolinamide counterpart.     

NBS as an efficient catalyst for the synthesis of 1,5-benzodiazepine derivatives under mild conditions

Various biologically important 1,5-benzodiazepine derivatives were efficiently synthesized in excellent yields using catalytic amounts of NBS (10 mol %). This inexpensive, nontoxic, and readily available catalyst efficiently catalyzes the condensation of several aromatic as well as aliphatic ketones with substituted o-phenylenediamines.     

An efficient catalyst for ring opening of epoxides with phenol and thiophenol under solvent-free conditions

An efficient and rapid procedure for ring opening reaction of various epoxides with phenol and thiophenol derivatives was developed. The procedure can be obtained at room temperature under solvent-free condition in presence of (C₄H₁₂N₂)₂[BiCl₆]Cl·H₂O (1 mol %). This catalyst can be reused several times without significant loss of activity.     

Selenocarboxamides as new reagents for stereospecific deoxygenation of epoxides under mild conditions

Selenocarboxamides have been found to be efficient reagents for converting epoxides into olefins stereospecifically in high yields under mild conditions.     

Green and efficient cycloaddition of CO_2 toward epoxides over thiamine derivatives/GO aerogels under mild and solvent-free conditions

Thiamine derivatives that are cheap, readily available, non-toxic and green are used as heterogeneous catalyst for the generation of cyclic carbonates through cycloaddition of CO_2 to epoxides without the need of co-catalyst and solvent. The interaction between thiamine hydrochloride(VB_1-Cl) and substrates(CO_2 and propylene oxide) was proven by ultraviolet-visible spectroscopy and ~1H nuclear magnetic resonance analysis, and it is deduced that the synergistic action among multi-functional groups(hydroxyl, halide anion and amine) is a favorable factor for cycloaddition reaction. A series of VB_1/GO aerogels were facilely prepared through the addition of aqueous VB_1 derivatives to a suspension of GO in ethanol at room temperature. It was found that the aerogel generated through the interaction of VB_1-Cl with GO shows catalytic activity and stability higher than those of VB_1-Cl. It is because the electrostatic interaction between GO and VB_1-Cl enhances the nucleophilicity and leaving ability of anion. The effects of reaction temperature, catalyst loading, CO_2 pressure and reaction time on CO_2 cycloaddition to propylene oxide were thoroughly studied.     

A manganese/copper bimetallic catalyst for C-N coupling reactions under mild conditions in water

An efficient and convenient bimetallic MnF₂/CuI catalyst in combination with trans-1,2-diaminocyclohexane has been developed for the cross-coupling of nitrogen heterocycles with aryl halides in water at moderate temperature. A variety of nitrogen nucleophiles including pyrazole, 7-azaindole, indazole, indole, pyrrole and imidazole afforded the corresponding products in moderate to good yields (up to 94%) under the described arylation conditions.     

A highly active catalyst for the reductive cyclization of ortho-nitrostyrenes under mild conditions

A mild and efficient method for the palladium-catalyzed reductive cyclization of ortho-nitrostyrenes to afford indoles is reported. Treatment of ortho-nitrostyrenes with 0.1 mol% palladium (II) trifluoroacetate [Pd(TFA)₂] and 0.7 mol% 3,4,7,8-tetramethyl-1,10-phenanthroline (tm-phen) in DMF at 15 psig CO and 80 °C afforded indoles in good to excellent yields. When the reaction was conducted in toluene, the corresponding N-hydroxyindole was isolated. A mechanism that accounts for the formation of N-hydroxyindole is proposed.     

Magnetically separable Pd catalyst for highly selective epoxide hydrogenolysis under mild conditions

A magnetically separable palladium catalyst was synthesized simply through a sol-gel process incorporating palladium nanoparticles and superparamagnetic iron oxide nanoparticles in aluminum oxyhydroxide matrix, which is highly active and selective for epoxide hydrogenolysis at room temperature under 1 atm H2. The catalyst was recycled for 25 times without loss of the activity.     

N-Doped porous carbon supported palladium nanoparticles as a highly efficient and recyclable catalyst for the Suzuki coupling reaction

A new catalyst, Pd particles supported on the N-doped porous carbon(PC) derived from Zn-based metal–organic frameworks(zeolitic imidazolate framework: ZIF-8), was successfully prepared for the first time.The as-prepared catalyst was designated as N-doped PC-Pd, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscope, N_2 adsorption and inductively coupled plasma atomic emission spectroscopy. The N-doped PC-Pd composite exhibited high catalytic activity toward the Suzuki–Miyaura cross-coupling reactions. The yields of the products were in the range of 90%–99%. The catalyst could be readily recycled and reused at least 6 consecutive cycles without a significant loss of its catalytic activity.     

Phosphine-free hydrazone-Pd complex as the catalyst precursor for a Suzuki-Miyaura reaction under mild aerobic conditions

[reaction: see text] Glyoxal bis(N-methyl-N-phenylhydrazone) (1) and its related compounds such as 2-pyridinecarboxaldehyde N-methyl-N-phenylhydrazone (3) were prepared and examined as ligands for the Suzuki-Miyaura cross-coupling reaction of aryl halides and arylboronic acids. We found phosphine-free catalysts, such as Pd(OAc)(2)/hydrazone ligand 1 or 3, to be efficient catalysts for a variety of substrates to produce the coupling products in good yields.     

Iron salt, a cheap, highly efficient and environment-friendly metal catalyst for Se-Se bond cleavage and the further reaction with methylenecyclopropanes under mild conditions

FeCl₃ was found to be a good catalyst in Se-Se bond cleavage. Further electrophilic additions to methylenecyclopropanes provide a convenient access to diphenylselenylcyclobutanes. Comparing with other Lewis acids, FeCl₃ is much cheaper and the reaction conditions are milde and more tolerance to air and moisture.