Subhajit Dinda

Highly facile homogeneous epoxidation of olefins using oxo-diperoxo tungstate(VI) complex as catalyst, bicarbonate as co-catalyst and hydrogen peroxide as a terminal oxidant

Addition of a dilute acetic acid solution of 8-quinolinol to an H2O2 solution of freshly precipitated H2WO4·2H2O furnishes a yellow adduct [WO(O2)2·2QOH] 1 which, on crystallization from a suitable solvent, affords orange-yellow complex [WO(O2)(QO)2] 2. When 2 reacts stoichiometrically with olefinic compounds in a 1∶1 molar ratio, the respective olefins are epoxidized and 2 is converted to the orange-red [WO2(QO)2] 3. When 1 is treated with an excess of H2O2 (greater than 6 equiv.) and PPh4Cl, an anionic light yellow complex PPh4[WO(O2)2(QO)] 4 is obtained. 4 reacts with cyclopentene (a representative olefin) in a 1∶1 molar ratio producing cyclopentene oxide and itself is converted to PPh4[WO2(O2)(QO)] 5. If the above reaction is conducted at a 1∶2 molar ratio (instead of 1∶1) then 2 moles of the corresponding epoxide is formed and 4 is converted to PPh4[WO3(QO)] 6. All these peroxo complexes have remarkable catalytic efficiencies in the epoxidation of olefinic compounds when used in tandem with NaHCO3 as co-catalyst and H2O2 as oxidant in a CH3CN medium at room temperature, the method being green and economical. The catalyst 4under the above experimental conditions shows so far unmatched efficiency in epoxidizing a wide variety of olefinic substrates.

Syntheses, spectroscopic and X-ray structure analyses of two dioxouranium (VI) complexes : supramolecular framework built from O-H...O, C-H...O and stacking interactions

Abstract Two dioxouranium(VI) complexes, [UO2(PBHA)2(DMSO)] (I) and [UO2(SALOP)(H2O)] (II), PBHA = N-phenyl benzohydroxamate, DMSO = dimethyl sulfoxide, SALOP = N,N′-bis (salicylidene)-o-phenylene diaminate have been synthesized, and characterized by spectroscopic and X-ray studies. Both compounds (I) and (II) crystallize in orthorhombic system with space group Pbca. The molecules in (I) are linked by intermolecular C–H…O hydrogen bonds into 32-membered tetrameric clusters (U4C12O8N4H4), which are further connected via uranyl oxygen atoms forming a three-dimensional supramolecular framework. In (II), intermolecular O—H…O hydrogen bonds between molecules related by inversion and translation generate infinite zigzag chains of R22(8) rings running along the [010] direction. The parallel chains are interlinked through C—H…O hydrogen bonds producing a complex supramolecular architecture in (II).

Synthesis, spectroscopic characterization and X-ray structure analyses of two uranyl complexes

Abstract The synthesis, spectroscopic characterization and crystal structures of two uranyl complexes, [UO2(SALEN)(DMF)] (1) and [UO2(BPHA)2(DMF)] (2) {SALEN = N,N′-ethylenebis(salicylimine), DMF = N,N-dimethylformamide, BPHA = N-phenyl benzohydroxamate} are described. The coordination geometry around the metal center in the mononuclear complexes can be best described as distorted pentagonal bipyramidal with an almost linear uranyl moiety. In addition to the van der Waal´s interactions, the crystal packing in the complexes is stabilized by weak intermolecular C–H…O hydrogen bonds involving the uranyl oxygen atoms, so generating two-dimensional arrays in both crystal structures.