Shu-Liang Zang

Olefin epoxidation with hydrogen peroxide using octamolybdate-based self-separating catalysts

Mo8O264− based organic polyoxomolybdate salts of general formula [Hmim]4Mo8O26 (Hmim = 1-hexyl-3-methylimidazolium), [Dhmim]4Mo8O26 (Dhmim = 1,2-dimethyl-3-hexylimidazolium) and [Hpy]4Mo8O26·H2O (Hpy = 1-hexylpyridinium) have been prepared and characterized. These compounds were applied as catalysts for olefin epoxidation using hydrogen peroxide (H2O2) as oxidant in CH3CN. The polyoxomolybdate salts exhibit excellent catalytic performance and are also self-separating, a great advantage for catalyst recycling. The catalysts can be reused for at least 10 runs without significant loss of activity.

(N-Salicylidene)aniline Derived Schiff Base Complexes of Methyltrioxorhenium(VII): Ligand Influence and Catalytic Performance

Methyltrioxorhenium(VII) (MTO) readily forms 1:1 adducts with several N-(salicylidene)aniline derived Schiff bases. If the aromatic rings of the N-(salicylidene)aniline ligands display non-donating or electron withdrawing substituent groups, the resulting MTO adducts show good activities in olefin epoxidations. However, steric effects seem to play a major role, leading often to instable o- and m-Schiff base-MTO adducts, while p-substituted Schiff bases usually lead to more stable adducts. In catalysis, electron-withdrawing substituents on the aniline moiety lead to better catalysts than electron donating ones. The gap between good catalysts and instable or non-existing compounds, however, is small. The general tendency, however, that good donors on the Schiff base ligands lead to shorter Re-O(Schiff base) bridges and lower catalytic activity, while the opposite is true with acceptor ligands on the Schiff bases, seems to be quite clear.

Oxidation Reactions Catalyzed by Polyoxomolybdate Salts

Ionic compounds containing the polyoxomolybdate anion [Mo6O19]2- and [(n-C4H9)4P]+ (tetrabutylphosphonium), [(n-C4H9)3P(n-C14H29)]+ (tributyl (tetradecyl)phosphonium), [Bmim]+ (1- butyl-3-methylimidazolium) and [Dbmim]+ (1,2-dimethyl-3-butylimidazolium) cations were prepared and characterized, including the determination of three of the solid state structures by singlecrystal X-ray diffraction. These compounds were applied as catalysts for the epoxidation of olefins with urea hydrogen peroxide (UHP) as oxidant in the ionic liquid [Bmim]PF6. Additionally, the oxidation of sulfides to sulfoxides with hydrogen peroxide (H2O2) in several solvents was investigated. The polyoxomolybdate catalysts showed a good performance for epoxidation of olefins as well as for oxidation of sulfides. Furthermore, the catalysts can be recycled several times in oxidation reactions. We present this methodology for the oxidation reaction in a simple, economically, technically, and environmentally benign manner Graphical Abstract Oxidation Reactions Catalyzed by Polyoxomolybdate Salts

Synthesis and Characterization of Imidazolium Perrhenate Ionic Liquids

A series of air- and water-stable imidazolium perrhenate-based room-temperature ionic liquids [(RT)ILs] of the type [Cnmim][ReO4] (Cnmim = 1-CnH2n+1-3-methylimidazolium, n = 2, 4, 5, 6, 8, 10, 12) have been synthesized and characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and elemental analysis (EA). The effect of the variation of the alkyl chain length on physical properties such as melting point, thermal stability, density, and conductivity was examined Graphical Abstract Synthesis and Characterization of Imidazolium Perrhenate Ionic Liquids