Syntheses of chromium(III) complexes with Schiff-base ligands and their catalytic behaviors for ethylene polymerization

A series of chromium(III) complexes LCrCl3 (4a-c) bearing chelating 2,2'-iminodiphenyisulfide ligands [L = (2-ArMeC=NAr)(2)S] was synthesized in good yields from the corresponding ligands and CrCl3.(THF). Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display moderate activities towards ethylene polymerization, and produce highly linear polyethylenes with broad molecular weight distribution. Polymer yields, catalyst activities and the molecular weights, as well as the molecular weight distributions of the polymers can be controlled over a wide range by the variation of the structures of the chromium(III) complexes and the polymerization parameters, such as Al/Cr molar ratio, reaction temperature and ethylene pressure.

Synthesis, characterization, crystal structure and magnetic property of asymmetrical double Schiff base heterotrinuclear complex: Cu(II)-Co(II)-Cu(II)

An asymmetrical double Schiff-base Cu(II) mononuclear complex, HCuLp (H(3)Lp is N-3-carboxylsalicylidene-N'-5-chlorosalicylaldehyde-1,3-diaminopropane) and a heterometal trinuclear complex with double molecular structure (CuLp)(2)Co center dot 5H(2)O have been synthesized and characterized by means of elemental analyses, IR and electronic spectra. The crystal structure of the heterotrinucler complex was determined by X-ray analysis. Each asymmetric unit within the unit cell of the complex contains two heterotrinuclear neutral molecules (a) [CuLpCoCuLp], (b) [(CuLpH(2)O) CoCuLp] and four uncoordinated water molecules. In the two neutral molecules, the central Co2+ ions are located at the site of O-6 with a distorted octahedral geometry, one terminal Cu2+ ion (Cu(3)) at the square-pyramidal environment of N2O3, and the other three at the square planar coordination geometry with N2O2 donor atoms. Magnetic properties of the heterotrinucler complex have been determined in the temperature range 5-300 K, indicating that the interaction between the central Co2+ ion and the outer Co2+ ions is antiferromagnetic.

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spectroscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers (SAMs). A carboxylic acid-terminated thiol, such as thioctic acid (1,2-dithiolane-3-pentanoic add), was self-assembled on gold electrodes. Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)(6)(3-) as a probe. The surface pK(a) of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 +/- 0.1 and 5.8 +/- 0.1, respectively. The method is compared with other methods of monolayer pK(a) measurement.

Studies of the ortho effect in fragmentations of acetyl ion adducts of disubstituted benzenes

The ion-molecule reactions of disubstituted benzenes under chemical ionization conditions with acetyl chloride as reagent gas were examined, and the fragmentation reactions of the adduct ions (mostly proton and acetyl ion adducts) were studied by collision-induced dissociation. Electron-releasing substituents favored the adduct reactions, and electron-withdrawing groups did not. The position and properties of substituting groups had an effect on the relative abundances of the adduct ions. Several examples of the ortho effect were observed. The fragmentation reaction of the adduct ions formed by ortho-benzenediamine with the acetyl ion was similar to the reductive alkylation reaction of amines in the condensed phase. Copyright (C) 2001 John Wiley & Sons, Ltd.

Metal ion adducts in the structural analysis of ginsenosides by electrospray ionization with multi-stage mass spectrometry

The effect of metal (Li+, Na+, K+, Ag+) cationization on collision-induced dissociation of ginsenosides was investigated by electrospray ionization mass spectrometry combined with multi-stage mass spectrometry (ESI-MSn). The fragments of sodiated and lithiated molecules give valuable structural information regarding the nature of the aglycone and the sequence and linkage information of sugar moieties. However, the number and relative abundances of fragment ions from lithiated ginsenosides are significantly greater than for the sodiated species, The K+ adducts undergo glycosidic cleavages and very limited cross-ring reactions. The silver ion adducts fragment mainly through glycosidic cleavages. Copyright (C) 2001 John Wiley & Sons, Ltd.

Synthesis, structure characterization of the complexes of beta-alkoxycarbonylethyltin trichlorides with Schiff base ligands

Thirty - two title complexes (ROCOCHRCH2SnCl3)-C-1 . (2 - HOC6H4CH = NC6H4 - X) (R = Me, Et, n - Bu; R-1 = H, Me; X = H,4' - Cl, 3' - Pr, 3' - OH, 3', 4' - Cl-2, 4' - OMe) were synthesized and characterized by elemental analysis,UV - vis, IR, H-1 NMR. The crystal structure of n - BuOCOCH2CH2SnCl3 . (2 - HOC6H4CH - NC6H4OMe - 4') were determined by the X - ray diffraction analysis, The crystal belongs to monoclinic system, with a = 1.4661 (3)nm, b = 0.9307 (2)nm, c = 1.7888 (4)nm, beta = 94.04 (3)degrees, V = 2.4348nm(3), D-c = 1.581mg/m(3), Z = 4, F(000) = 1160, mu = 1.405mm(-1), R = 0.0354, R-w = 0,0486, space group: P2(1)/c. The complexes exist as a discrete monomer. The tin atom has a distorted octahedral geometry due to intramolecular coordination of the carbonyl oxygen and the phenolic oxygen of the Schiff base ligands, The coordination number of tin atom is 6.

Synthesis and crystal structure of chiral bis(cyclopentadienyl) samarium Schiff base complexes bearing intramolecular C-C bond formation and hydrogen transfer

SmCl3, reacted with CpNa (Cp = Cyclopentadienyl) in the ratio of 1:3 in THF, which then was reacted with (S)-(+)-N-1-(phenylethyl) salicylideneamine/toluene to yield the title complex, [GRAPHICS] The X-ray crystal structure determination of the title complex reveals that 1 is a dimer with intramolecular C-C bond formation and hydrogen transfer, which leads to the configuration turnover of the carbon atom at the benzyl position of the ligand, while those of the newly formed asymmetric centers may have either Ii or S type configurations. (C) 1998 Elsevier Science Ltd. All rights reserved.

Synthesis of the first mono(cyclopentadienyl)lanthanide Schiff base complex bearing C-2-symmetric tetradentate ligand: crystal structure of [(eta(5)-C5H5)Yb(mu-OC20H20N2O)](2)(mu-THF)(THF)

Reaction of YbCl3 with 3 equimolar CpNa (Cp = cyclopentadienide) in THF, followed by treatment with trans-(+/-)-N,N'-bis(salicylidene)-1,2-cyclohexanediamine led to the isolation of first mono(cyclopentadienyl) lanthanide Schiff base complex, [(eta(5)-C5H5)Yb(mu-OC20H20N2O)](2) (mu-THF)(THF) (1). The molecular structure of 1 shows that it is a dimer in which the two [(eta(5)-C5H5)Yb(mu-OC20H20N2O)] units connecting via a bridging THF oxygen and two bridging oxygen atoms from Schiff base ligands. (C) 1998 Elsevier Science S.A.