Novel (N‐heterocyclic carbene)Pd(pyridine)Br2 complexes for carbonylative Sonogashira coupling reactions: Catalytic efficiency and scope for arylalkynes,alkylalkynes and dialkynes

New N,N′‐substituted imidazolium salts and their corresponding dibromidopyridine–palladium(II) complexes were successfully synthesized and characterized. Reactions of palladium bromide with the newly synthesized N,N′‐substituted imidazolium bromides ( 2a and 2b ) in pyridine afforded the corresponding new N‐heterocyclic carbene pyridine palladium(II) complexes ( 3a and 3b ) in high yields. Their single‐crystal X‐ray structures show a distorted square planar geometry with the carbene and pyridine ligands in trans position. Both complexes show a high catalytic activity in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with arylalkynes, alkylalkynes and dialkynes.     

Gamma to alpha phase transformation in FeCoV alloys

The effects of filing FeCoV alloys with equiatomic FeCo and up to 14 at% V is studied by Mössbauer spectroscopy and X-ray diffraction. We observed that filing eliminates the paramagnetic component observed in samples in the form of plates. The filed material also presents a linear increase of the lattice parameter and a linear decrease of the average hyperfine field of the alpha phase due to extra low-field satellites with increasing vanadium contents. This indicates that filing produces a gamma to alpha phase transformation, which increases the amount of vanadium in solid solution in the FeCo alpha phase.     

Characterization of phases in the Fe-Nb system

The Fe-Nb system was investigated by means of X-ray diffraction and Mössbauer spectroscopy (at 300 and 77 K), in the range from 1 to 66.7 at%. We have found that the limit of solubility of Fe in Nb at 1100°C is between 3 and 4 at% Fe, and observed the coexistence of the Nb solid solution (Nbss) phase and Fe₂₁Nb₁₉ in the range from 4 to 40 at% Fe. The Mössbauer parameters of all the single phases are reported. The lattice parameters of Nbss phase present no significant variation with the Nb content. The X-ray pattern for the Fe₂₁Nb₁₉ phase could not be solved. The Laves phase Fe₂Nb presents Mössbauer and X-ray parameters that agree with the literature.     

A109Cd/109mAg generator

Sorption of Cd and Ag by a cation exchange resin has been studied at different molarities of nitric acid. The sorption capacity of Cd on a cation exchanger has been determined. A¹⁰⁹Cd/^109mAg generator is suggested, based on the sorption of Cd on AG 50W-X8 organic cation exchanger at 0.01M HNO₃.^109mAg is eluted with 0.2M NaCl, physiologically compatible for human use.     

Acid character control of bioactive glass/polyvinyl alcohol hybrid foams produced by sol–gel

Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of bioceramics with the flexibility of polymers. In previous work hybrid foams with 80% bioactive glass and 20% polyvinyl alcohol were prepared by the sol–gel method. The produced hybrids presented a high acidic character due to the catalysts added. In this work different methods to control the acidity and toxicity of the hybrids were also evaluated, through changes in the synthesis pH and use of different neutralization solutions. The hybrids were prepared with inorganic phase composition of 70%SiO₂–30%CaO and PVA fractions of 20–60% by the sol–gel method. The characterization of the obtained foams was done by FTIR, SEM, Raman Spectroscopy, Helium Picnometry and TGA. The immersion of hybrids in a calcium acetate solution was the most adequate neutralization method. The foams presented porosity of 60–85% and pore diameters of 100–500 μm with interconnected structure.     

Influence of the hydrotrope structure on the physical chemical properties of polyoxide aqueous solutions

The physical chemical properties of block substituted poly(ethylene oxide-propylene oxide) (PEO-PPO) block copolymer aqueous solutions were evaluated in the presence of two hydrotropes of different structures: sodium p-toluene sulfonate (NaPTS) and butyl monoglycol sodium sulfonate (NaBMGS). The critical micelle concentration and the cloud point of the copolymer solutions were displaced to higher concentration values, indicating that the solubility of the copolymer was increased in the presence of the hydrotropes. Temperature increased the micelle hydrodynamic radius, but concentration had a limited effect. Carbon-13 nuclear magnetic resonance (13C NMR) permitted the interaction between the surface-active agent and the hydrotrope to be evaluated: NaBMGS, which presented a more pronounced hydrotropic effect, interacts more effectively with the hydrophobic moiety of the surfactant, while NaPTS interacts rather mainly with the hydrophilic oxyethylenic groups. The results furnish experimental evidence to conclude that the hydrotropic phenomenon is specific in relation to both the hydrotrope and the solubilizate.     

Synthetically attractive chiral cyclopentenone building blocks conjugated with tetrahydro- and 2-oxotetrahydrofurans

Synthetically useful chiral building blocks (3aS,6aR)-1,3,3a,6atetrahydro-4H-cyclopenta[c]furan-4-one and (3aS,6aR)- 3a,6a-dihydro-1H-cyclopenta[c]furan-1,4(3H)-dione have been synthesized via a key allylsilane–allyl alcohol fragmentation pathway using (3aS,6S,6aR)-6-(trimethylsilyl)-3,3a,6,6a-tetrahydro-1H-cyclopenta[c]furan-1-one as an illustrative example.

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Novel azetidinones for carbapenems and fragmentation in the allylamine precursor analogue

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New palladium-bis(oxazoline)-phosphine complexes: synthesis,characterization and catalytic application in alkoxycarbonylation of alkynes

New cationic palladium-bis(oxazoline)-phosphine (Pd-BOX-PR₃) complexes (Pd-BOX-B and Pd-BOX-C) have been synthesized and characterized using ¹H, ¹³C and ³¹P NMR, FTIR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The new complexes were used as catalysts in the alkoxycarbonylation of alkynes with various alcohols as nucleophiles. The carbonylation has produced the gem-α,β-unsaturated ester isomer (3) in high regioselectivity and excellent yields. The catalyst systems have been optimized by screening the type of palladium complexes and also by varying the reaction parameters including the reaction time, solvent, and temperature. A mechanism of the catalytic cycle based on a N-protonated palladium bis(oxazoline) phosphine active species was proposed for the alkoxycarbonylation reaction.