Search results for "Onium"
showing 10 items of 2091 documents
Tris-pentasulfidorhodates(III). X-ray structure of (NH4)3[Rh(S5)3](H2O)2
1987
Abstract The crystal structure of the racemic dihydrated ammonium salt of the tris -pentasulfidorhodate(III) anion is compared with those of salts of the tris -pentasulfidoplatinate(IV) ion.
Lithium intercalation chemistry, microstructure and superconductivity in zirconium and hafnium nitride halides
2000
Abstract Lithium intercalation in β-MNX (M=Zr, Hf; X=Cl, Br) leads to superconducting compounds with critical temperatures between 12 and 24 K. The lithium uptakes after treatment of the host materials with n-butyllithium/hexane solutions are ca. 0.2 atoms per formula for β-ZrNCl and β-ZrNBr, and between 0.07 and 0.67 for β-HfNCl. Electrochemical lithiation experiments agree with the results obtained with chemical methods, as samples with larger capacity on discharge are also those having larger lithium contents after chemical lithiation. Variations exist in the electrochemical profiles of different batches for the three compounds indicating differences in the intercalation reaction pathway…
Determination of zirconium traces in polymers by ICP-IDMS - a powerful and fast method for routine testing of zirconium residues in polyolefins
1999
Zirconium trace analyses play an important role for polyolefins produced by modern catalytic processes with zirconium metallocenes. A reliable and fast routine testing method by inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) was therefore developed, which allows the determination of zirconium in polymers down to the low ng/g level. With respect to its precision, accuracy, and time-consumption this method is suitable for routine testing of production processes. A spike solution, enriched in the stable isotope 91Zr, was prepared and used for the isotope dilution procedure, which has the advantage of being an internal “one point” calibration method. The polyolefin sam…
Formation of arynezirconocenes from substituted diaryl bis (t-butylcyclopentadienyl) zirconium: application to the synthesis of new functionalizedort…
1991
The para-substituted diphenylzirconocenes [(t-BuCp)2Zr(p-C6H4R)2; R = Br, NMe2] (A) were easily obtained from the reaction of the appropriate organolithium reagent with bis(t-butylcyclopentadienyl)zirconium dichloride. Elimination of bromobenzene or N,N-dimethylaminobenzene from A by slight heating led to arynezirconocenes into which were inserted two equivalents of elementary chalcogens. As a result dichalcogenated zirconacycles [(t-BuCp)2ZrY2C6H3R; Y = S, Se] (B) were obtained. Complexes B constitute useful potential synthons in organic synthesis and a large family of new functionalized dichalcogenated benzenic compounds was prepared by reacting electrophiles. The structure of complexes B…
Zirconium and hafnium mono(alkyl) complexes containing a tridentate linked amido-tetramethylcyclopentadienyl ligand. Molecular structure of Hf(η5:η1:…
1998
Abstract Zirconium and hafnium complexes M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 (M=Zr, Hf) containing the tridentate 2-methoxyethylamido-functionalized tetramethylcyclopentadienyl ligand C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe have been synthesized by the reaction of the dilithium derivative Li 2 [C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe] with MCl 4 (THF) 2 . Selective monoalkylation of the dichloro complexes gave complexes of the type M( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)(R)Cl (R=CH 2 Ph, o -C 6 H 4 CH 2 NMe 2 ). The crystal structure of the hafnium dichloro complex Hf( η 5 : η 1 : η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 OMe)Cl 2 has been determined by X-ray crystal diffraction and sho…
Enantioselective Synthesis of Substituted Indoles Through Zirconium(IV)-Catalyzed Friedel–Crafts Alkylation
2012
The chiral complex of ( R )-3,3′-Br 2 -BINOL and zirconium tert -butoxide catalyzes the Friedel–Crafts alkylation of indoles with enones bearing an alkyl or fluorinated group at the β-position to give indoles having a side chain at the C3 position with a tertiary stereogenic center in good yields and with excellent enantioselectivities.
Pyrrolide-imine benzyl complexes of zirconium and hafnium: synthesis, structures, and efficient ethylene polymerization catalysis
2004
Abstract A series of pyrrolyl-imines HL1–6 was prepared by the condensation of pyrrole-2-carboxyaldehyde with different amines. The reaction of 2 equiv of pyrrolyl-imine with tetrabenzyl complexes of hafnium and zirconium M(CH2Ph)4 (M=Hf or Zr) gave dibenzyl complexes (L3–6)2M(CH2Ph)2, which were characterized by NMR spectroscopy and crystal structure analysis. NMR spectra of the complexes with secondary alkyl substituents at the imine nitrogen (isopropyl: 3a, 4-tert-butylcyclohexyl: 4a and 4b) suggest that rapid racemization between Δ and Λ configurations occurs in solution on the NMR time scale. The complexes with pyrrolide-imine ligands with a tertiary alkyl group such as tert-butyl (5a …
Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization
2001
Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed b…
Novel Porphyrin-Cholic Acid Conjugates as Receptors for Biologically Important Anions
2005
A series of novel receptors showing high binding affinity in aqueous media for biologically important anions are reported. These naturally chromophoric porphyrin-based receptors contain cholic acids connected via quaternary alkyl ammonium amido linkages.
The Effect of Bialaphos on Ammonium-Assimilation and Photosynthesis I. Effect on the Enzymes of Ammonium-Assimilation
1989
Abstract In this investigation, the effect of bialaphos (phosphinothricyl-alanyl-alanine) on the enzymes involved in NH4 +-assimilation - glutamine synthetase, glutamine-2-oxoglutarate aminotransferase, glutamate dehydrogenase - is examined and compared to the effect of phosphinothricin (glufosinate) on the same enzymes. Bialaphos was given to whole plants (in vivo) and to leaf homogenate (in vitro). The investigation showed that bialaphos has an inhibiting effect on glutamine synthetase in vivo, but not in vitro. In contrast to this, phosphinothricin inhibits glutamine synthetase in vitro as well as in vivo. It was found that bialaphos, similar to phosphinothricin, does not inhibit glutami…