Asymmetric Michael addition of aldehydes to nitroolefins catalyzed by L-prolinamide derivatives using phenols as co-catalysts

The asymmetric Michael addition of aldehydes to nitroolefins was investigated using L-prolinamide derivatives of 2-(2'-piperidinyl)pyridine as catalyst and a variety of phenols as co-catalyst. Extensive screening toward the effect of prolinamides, phenols, and solvents on this transformation revealed that a combination of (S)-2-(2'-piperidinyl)pyridine-derived trans-4-hydroxy-L-prolinamide 2c, (S)-1,1'-bi-2-naphthol, and dichloromethane was a promising system. This system was shown to be amenable to a rich variety of aldehydes and nitroolefins and afforded the nitroaldehyde products with excellent yield, enantiomeric excess (up to 99%) and diastereoselectivity ratio (up to 99/1), even in the case of 1 mol % catalyst loading and 1.5 equiv of aldehydes.

Surface plasmon resonance and electrochemistry for detection of small molecules using catalyzed deposition of metal ions on gold substrate

Small molecules are difficult to detect by conventional surface plasmon resonance (SPR) spectroscopy due to the fact that the changes in the refractive index resulted from the binding process of small biomolecules are quite small. Here, we report a simple and effective method to detect small biomolecule using SPR spectroscopy and electrochemistry by catalyzed deposition of metal ions on SPR gold film. As an example, the ascorbic acid-mediated deposition of Ag on gold film was monitored by in situ SPR spectrum. The deposition of Ag atom on gold film resulted in an obvious decrease of depth in SPR angular scan curves of reflectance intensity and minimum reflectivity angle. The depth change of the SPR reflectance intensity and minimum reflectivity angle curves mainly relied on the amount of Ag atom deposited on gold film that can be controlled by the concentration of ascorbic acid. By monitoring the deposition of Ag atom on gold film, ascorbic acid was detected in the concentration range of 2 x 10(-5) M to 1 x 10(-3) M. After each of detections, the SPR sensor surface was completely regenerated by a potential step that stripped off the Ag atom. Furthermore, the regeneration process of the sensor surface provides the feasibility for detecting the concentration of ascorbic acid by electrochemical method.

Synthesis of bis(amine anhydride)s for novel high T(g)s and organosoluble poly(amine imide)s by palladium-catalyzed amination of 4-chlorophthalide anhydride

Two novel bis(amine anhydride)s, NN-bis(3,4-dicarboxyphenyl)aniline dianhydride (I) and N,N-bis(3,4-dicarboxyphenyl)-p-tert-butylaniline (II), were synthesized from the palladium-catalyzed amination reaction of N-methyl-protected 4-chlorophthalic anhydride with arylamines, followed by alkaline hydrolysis of the intermediate bis(amine-phthalimide)s and subsequent dehydration of the resulting tetraacids. The X-ray structures of anhydride I and II were determined. The obtained dianhydride monomers were reacted with various aromatic diamines to produce a series of novel polyimides. Because of the incorporation of bulky, propeller-shaped triphenylamine units along the polymer backbone, all polyimides exhibited good solubility in many aprotic solvents while maintaining their high thermal properties. These polymers had glass transition temperatures in the range of 298-408 degrees C. Thermogravimetric analysis showed that all polymers were stable, with 10% weight loss recorded above 525 degrees C in nitrogen.The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 95-164 MPa, 8.8-15.7%, and 1.3-2.2 GPa, respectively.

Guanidine/Pd(OAc)(2)-catalyzed room temperature Suzuki cross-coupling reaction in aqueous media under aerobic conditions

A highly efficient Pd(OAc)(2)/guanidine aqueous system for the room temperature Suzuki cross-coupling reaction has been developed. The new water-soluble and air-stable catalyst Pd(OAc)(2)(.)(1f)(2) from Pd(OAc)(2) and 1,1,3,3-tetramethyl-2-n-butylguanidine (1f) was synthesized and characterized by X-ray crystallography. In the presence of Pd(OAc)(2)(.)(1f)(2), coupling of arylboronic acids with a wide range of aryl halides, including aryl iodides, aryl bromides, even activated aryl chlorides, was carried out smoothly in aqueous solvent to afford the cross-coupling products in good to excellent yields and high turnover numbers (TONs) (TONs up to 850 000 for the reaction of 1-iodo-4-nitrobenzene and phenylboronic acid). Furthermore, this mild protocol could tolerate a broad range of functional groups.

Alternating copolymerization of carbon dioxide and propylene oxide catalyzed by (R,R)-SalenCo(III)-(2,4-dinitrophenoxy) and Lewis-basic cocatalyst

A binary catalyst system of a chiral (R,R)-SalenCo(III)(2,4-dinitrophenoxy) (salen = N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-diphenylethylenediimine) in conjunction with (4-dimethylamino)pyridine (DMAP) was developed to generate the copolymerization of carbon dioxide (CO2) and racemic propylene oxide (rac-PO). The influence of the molar ratio of catalyst components, the operating temperature, and reaction pressure on the yield as well as the molecular weight of polycarbonate were systematically investigated. High yield of turnover frequency (TOF) 501.2 h(-1) and high molecular weight of 70,400 were achieved at an appropriate combination of all variables. The structures of as-prepared products were characterized by the IR, H-1 NMR, C-13 NMR measurements. The linear carbonate linkage, highly regionselectivity and almost 100% carbonate content of the resulting polycarbonate were obtained with the help of these effective catalyst systems under facile conditions.

Monooxychlorophosphine as a novel and efficient ligand for palladium-catalyzed suzuki-miyaura cross-coupling of aryl chlorides

A new sterically hindered monooxychlorophosphine was synthesized and the complex generated in situ from its reaction with Pd-2(dba)(3) promoted the Suzuki-Miyaura reactions of arylboronic acids with aryl chlorides in good yields.

One-pot synthesis of polyimides via Ni-catalyzed coupling of bis(chlorophthalimide)s

A one-pot synthesis method for the preparation of polyimides containing biphenyl units was developed via nickel-catalyzed coupling reaction of bis(chlorophthalimide)s which were prepared from chloroplithalic anhydrides and diamines in xylene. The resulting polyimides had inherent viscosities of above 0.60dL g(-1). In the meantime, the copolymerizations from a mixture of three isomeric bis(chlorophthalimide)s gave the polymers with inherent viscosities of 0.36-0.55 gdL(-1). The solubility and film formability of the copolymers were better than those of homopolymers from bis(4-chlorophthalimide). The 10% weight loss of these polyimides was between 470 and 531 degrees C.

Enantioselective iodolactonization catalyzed by chiral quaternary ammonium salts derived from cinchonidine

Chiral quaternary ammonium salts derived from cinchonidine have been applied to catalyze the stereoselective iodolactonizations of trans-5-aryl-4-pentenoic acids leading to a mixture of two regioselectively iodolactonized products with fair to excellent yield (37-98%) and moderate enantioselectivity (exo = 42.0% ee, endo = 31.0% ee) under mild conditions. This work is the first example of asymmetric iodolactonization reaction in the presence of less than a stoichiometric amount of chiral reagent.

Copolymerization of dichlorodiphenylsulfone with bis(chlorophthalimide) catalyzed by NiBr2/PPh3/Zn

A new high-performance material, poly(sulfone-imide) was prepared by Ni(0)-catalyzed coupling of aromatic dichlorides containing imide structure and 4,4'-dichlorodiphenylsulfone. The copolymers were produced with high yield and moderate to high inherent viscosities of 0.52-1.13 dL/g. Wide-angle X-ray diffractograms revealed that the polymers were amorphous. Most of the polymers exhibited good solubility and could be readily dissolved in various solvents such as N-methyl-2-pyrrolidinone(NMP) and N,N-dimethylacetamide (DMAc). These polysulfone-imides had glass-transition temperatures between 317 and 345 degreesC and 10% weight loss temperatures in the range of 450476 degreesC in nitrogen atmosphere. The tough polymer films, obtained by casting from cresol solution, had a tensile strength range of 21 158 MPa and a tensile modulus range of 2.1-3.3 GPa.

Synthesis of cyclic carbonates from CO2 and epoxides catalyzed by hexaalkylguanidinium halides

Hexaalkylguanidinium halides exhibit an efficient catalytic activity in the synthesis of cyclic carbonates from, epoxides and carbon dioxide. By this method cyclic carbonates can be obtained in a high yield and a high selectivity at a low temperature and atmospheric pressure. This procedure is easy for the product isolation and recycling of the catalyst.

Bronsted guanidine acid-base ionic liquids: Novel reaction media for the palladium-catalyzed Heck reaction

Bronsted acid-base ionic liquids (GILs) based on guanidine and acetic acid are efficient reaction media for palladium-catalyzed Heck reactions. They offer the advantages of high activity and reusability. GIL2 plays multiple roles in the reaction: it could act as solvent, as a strong base to facilitate beta-hydride elimination, and as a ligand to stabilize activated Pd species.

PEG-supported dipyridyl ligand for palladium-catalyzed Suzuki and Suzuki-type reactions in PEG and aqueous media

An air- and water-stable PEG-supported bidentate nitrogen ligand is prepared and its applications in the palladium-catalyzed Suzuki reaction of aryl halides with arylboronic acids in PEG and Suzuki-type reaction of aryl halides with sodium tetraphenylborate in aqueous media are reported. The homogeneous catalyst system is environmentally friendly and offers the advantages of high activity, reusability and easy separation.

Nickel complexes catalyzed Heck reaction of iodobenzene and methyl acrylate

Nickel appears the most promising for the replacement of palladium among the inexpensive transition metals for that it is active for Heck reaction and about 500 times cheaper than palladium. In this article, we describe our recent results in the area of nickel-catalyzed Heck vinylations. Main focus is on the influence of ligand concentration in different organic solvents and the effects of the addition of water. The conversion is high in NMP and increases with increasing of PPh3/Ni ratio; in ethanol and toluene the conversion presents a maximum value on Ni(PPh3)(2). The effect of the addition of water is sensitive to the concentration of PPh3 and the nature of solvent, it was well explained with the formation and transfer of the active species in the different solvent systems.

Neodymium oxide co-catalyzed melt free radical grafting of maleic anhydride onto co-polypropylene by reactive extrusion

Rare earth oxide, neodymium oxide (Nd2O3), CO-catalyzed melt grafting of maleic anhydride (MAH) onto co-polypropylene (co-PP) in the presence of dicumyl peroxide (DCP) was carried out by reactive extrusion. The experimental results reveal that the addition of Nd2O3 as a coagent leads to an enhancement in both MFR and the grafting degree of MAH, along with a simultaneous decrease in the gel content. When the Nd2O3 concentration is 6.0 mmol%, the increment of the grafting degree of MAH maximally is up to about 20% compared with the related system without adding Nd2O3, and the gel content decreases simultaneously to a very low level of about 3%. Attenuated total reflection FTIR (ATR-FTIR) indicates that the gel in the graft copolymers mainly arise from the cross-linking reaction between ethylene units of co-PP. A reasonable reaction mechanism has been put forward on the basis of our experimental results and other mechanisms reported in the literature. We also tentatively explain above results by means of synergistic effect between DCP and Nd2O3, which causes a higher concentration of the macroradical, in particular the tertiary macroradical.