Direct arylation of oxazole and benzoxazole with aryl or heteroaryl halides using a palladium-diphosphine catalyst

Through the use of PdCl(dppb)(C₃H₅) as a catalyst, a range of aryl bromides and chlorides undergoes coupling via C-H bond activation/functionalization reaction with oxazole or benzoxazole in good yields. This air-stable catalyst can be used at low loadings with several substrates. Surprisingly, better results in terms of substrate/catalyst ratio were obtained in several cases using electron-excessive aryl bromides than with the electron-deficient ones. This seems to be mainly due to the relatively low thermal stability of some of the 2-arylbenzoxazoles formed with electron-deficient aryl halides. With these substrates, in order to obtain higher yields of product, the reactions had to be performed at a lower temperature (100-120 °C) using a larger amount of catalyst. On the other hand, in the presence of the most stable products, the reactions were performed at 150 °C using as little as 0.2 mol% catalyst. Arylation of benzoxazole with heteroaryl bromides also gave the coupling products in moderate to high yields using 0.2-5 mol% catalyst. With this catalyst, electron-deficient aryl chloride such as 4-chlorobenzonitrile, 4-chloroacetophenone or 2-chloronitrobenzene have also been used successfully.     

Synthesis,characterization, electrochemical behaviour and catalytic activity of manganese(II) complexes with linear and tripodal tetradentate ligands derived from Schiff bases

New manganese(II) complexes, [Mn(H₂L)(H₂O)₂]Cl₂· xH₂O, with linear and tripodal tetradentate ligands have been synthesized and characterized by elemental analysis, molar conductance, i.r. spectra, magnetic measurements and electronic and e.s.r. spectra. The data show that the ligands are neutral and coordinate to manganese in a tetradentate manner; the other axial sites are occupied by the water molecules. Magnetic and e.s.r. data show that manganese(II) adopts a high-spin configuration in the complexes. The electrochemical behaviour of the complexes, determined by cyclic voltammetry, shows that the chelate structure, ligand geometry and electron donating effect of the ligand substituents are among the factors influencing the redox potentials of the complexes. In addition, we note that linear ligands stabilize the manganese(III) state to a greater extent than tripodal ligands and their complexes vigorously catalyse the disproportionation of hydrogen peroxide in the presence of added imidazole.     

Alpha-benzoinomixe: Extracting agent for uranium(VI), tungsten(VI), molybdenum(VI) and some transition metals of the iron family

The effect of pH on the percent extraction of vanadium(V), iron(II), cobalt(II), nickel(II), copper(II), molybdenum(VI), tungsten(VI) and uranium(VI) by -benzoinoxime in different solvents has been studied. The maximum recovery is not appreciably affected by the nature of the solvent, but occurs at different pH values for different metals. The pH corresponding to maximum extraction increases with increasing hydrolysis pK of the species in aqueous solution, and decreases with increasing stability constant of the complexes formed. Alpha-benzoinoxime allows the separation of these metal ions into three groups: V(V), Mo(VI) and W(VI) are extracted at pH=2, U(VI) at pH=5, Fe(II), Cu(II), Co(II) and Ni(II) at around pH=10.