Home About us Contact
|
Home About us Contact | ||
|
|
||
Vanadium Complexes (vanadium + complex)
Selected AbstractsEnantioselective Oxidation of Sulfides with Hydrogen Peroxide Catalyzed by Vanadium Complex of Sterically Hindered Chiral Schiff Bases.CHEMINFORM, Issue 13 2005Yong-Chul Jeong Abstract For Abstract see ChemInform Abstract in Full Text. [source] Highly Efficient Direct Carboxylation of Propane into Butyric Acids Catalyzed by Vanadium ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2007Marina Abstract A direct and highly efficient carboxylation of propane by carbon monoxide into butyric acids (mainly isobutyric and, in a smaller amount, n -butyric), in the presence of potassium peroxodisulphate (K2S2O8) and in trifluoroacetic acid solution, has been achieved by using a vanadium catalytic system based on Ca[V{ON(CH(CH3)COO)2}2] (synthetic amavadine), its model compounds Ca[V{ON(CH2COO)2}2] or [VO{N(CH2CH2O)3}] , other simpler vanadium compounds, such as [VO(acac)2] or VOSO4, are less active. Overall yields (based on propane) of carboxylic acids up to 70,% and TON values up to 18.4×103 have been reached. The effects of various factors such as the propane and carbon monoxide pressures, temperature, time, catalyst amount and radical traps have been investigated, the reactions are shown to proceed via both C - and O -centred radicals, with K2S2O8 playing the role of an oxidant via a free radical mechanism. [source] Chiral Self-Dimerization of Vanadium Complexes on a SiO2 Surface: The First Heterogeneous Catalyst for Asymmetric 2-Naphthol Coupling.CHEMINFORM, Issue 15 2005Mizuki Tada Abstract For Abstract see ChemInform Abstract in Full Text. [source] Insulin mimetic effects of macrocyclic binuclear oxovanadium complexes on streptozotocin-induced experimental diabetes in ratsDIABETES OBESITY & METABOLISM, Issue 6 2003B. Ramachandran Aim:, The vanadium complexes so far tested for their insulin mimetic effects are either mono- or binuclear and contain only acyclic ligands. The leaching or hydrolysis of vanadyl ions from these complexes is much easier, and hence they elicit side effects. In the present study, a new binuclear macrocyclic oxovanadium complex was synthesized, and its efficacy was studied on streptozotocin (STZ)-induced diabetic rats over a period of 30 days. Methods:, The insulin mimetic effect of the complex was tested on the blood sugar level in the STZ-diabetic rats and on the activities of the carbohydrate-metabolizing enzymes present in the liver. Results:, Administration of vanadium complex to STZ-induced diabetic rats decreased blood glucose levels from hyperglycaemic to normoglycaemic when compared to diabetic rats. The activity of carbohydrate-metabolizing enzymes such as hexokinase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen content were increased to near normal in vanadium complex-administered diabetic rats. The biochemical studies such as assay of blood urea and glutamate oxaloacetate transaminases revealed that the complex is not toxic to the system. Conclusion:, The nontoxic nature of this complex may be due to the presence of the vanadyl ions in an intact macrocyclic form. Further, the vanadyl ions present in the macrocyclic binuclear oxovanadium complex are very close to each other, and this may enhance the insulin mimetic activity by synergic effect. [source] Synthesis, Crystal Structure and Characterisation of a Novel Chiral Mixed-Valence Vanadium Oxide Hybrid, [V5O11(dien)3]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2005Ming-Lai Fu Abstract The novel chiral mixed-valence vanadium oxide hybrid [V5O11(dien)3] (1) (dien = NH2C2H4NHC2H4NH2) has been synthesised by a hydrothermal reaction of V2O5 and dien in aqueous solution and characterised by elemental analysis, IR spectroscopy, TG-DSC analysis, magnetism, EPR spectroscopy, single-crystal X-ray diffraction and powder XRD. The X-ray diffraction analysis revealed that the structure of 1 can be regarded as being constructed from two [VVO4]3, groups bicapping three [VIVO(dien)]2+ units to form a discrete asymmetric pentanuclear vanadium complex with the dien ligands coordinating directly to the vanadium(IV) centres. Compound 1 exhibits an interesting tube-like 3D supramolecular structure due to abundant hydrogen-bonding interactions between the oxygen atoms of the inorganic backbone and the hydrogen atoms of the dien ligands from adjacent molecules. The variable-temperature magnetic susceptibility data of 1 suggest a weak ferromagnetic interaction among V4+ ions in the cluster. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single-Centre and Ziegler,Natta Catalysts for Ethylene PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 21 2008Rubin Huang Abstract The ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n -PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3,n prepared from the reaction of AlR3 with MgCl2,·,1.1EtOH. These supports are characterized by additional peaks in the X-ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species. [source] Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical ShiftsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004Sonja Grigoleit Dr. Abstract Both zero-point and classical thermal effects on the chemical shift of transition metals have been calculated at appropriate levels of density functional theory for a number of complexes of titanium, vanadium, manganese and iron. The zero-point effects were computed by applying a perturbational approach, whereas classical thermal effects were probed by Car,Parrinello molecular dynamics simulations. The systematic investigation shows that both procedures lead to a deshielding of the magnetic shielding constants evaluated at the GIAO-B3,LYP level, which in general also leads to a downfield shift in the relative chemical shifts, ,. The effect is small for the titanium and vanadium complexes, where it is typically on the order of a few dozen ppm, and is larger for the manganese and iron complexes, where it can amount to several hundred ppm. Zero-point corrections are usually smaller than the classical thermal effect. The pronounced downfield shift is due to the sensitivity of the shielding of the metal centre with regard to the metal,ligand bond length, which increase upon vibrational averaging. Both applied methods improve the accuracy of the chemical shifts in some cases, but not in general. [source] | ||||||||||