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Chelating Units (chelating + unit)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Iminohydroxamato Early and Late Transition Metal Halide Complexes , New Precatalysts for Aluminoxane-Cocatalyzed Olefin Insertion Polymerization

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004
Alexander Krajete
Abstract We report on new families of non-metallocene metal precatalysts for olefin polymerization with titanium, zirconium, vanadium and nickel as the active metal sites. The novel ligand design concept is based on iminohydroxamic acids and their derivatives as the principal chelating units. Various anionic and neutral [N,O] and [N,N] ligand systems are easily accessible by a modular synthetic sequence of imidoyl chlorides with substituted hydroxylamines or hydrazines, respectively. Steric protection of the metal coordination site, a necessary requirement for suppression of chain termination pathways of non-metallocene catalysts, is brought about by bulky aryl substituents on the imino nitrogen atoms. Crystal structures of some of the hydroxamato ligands reveal interesting intermolecular hydrogen-bridged structures, whereas in the solid-state structure of one titanium precatalyst a five-membered chelate was observed, in line with the design principle of these systems. Preliminary ethylene polymerization studies with methylaluminoxane-activated metal complexes (M = Ti, Zr, V, Ni) show that the most active systems are [N,O]NiBr2 catalysts containing neutral O -alkyl iminohydroxamate ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Iron(III) Chelation: Tuning of the pH Dependence by Mixed Ligands

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2003
Anne-Marie Albrecht-Gary
Abstract The iron(III) chelating properties of two heteropodands with 8-hydroxyquinoline and catechol binding groups were examined and compared to those of the corresponding homopodal analogues, O-TRENSOX and TRENCAMS. Like the parent homopodands, the two heteropodands are based on the TREN scaffold and the chelating units are connected by amide groups, TRENSOX2CAMS having two 8-hydroxyquinoline and one catechol arms and TRENSOXCAMS2 one 8-hydroxyquinoline and two catechol moieties. The aqueous coordination chemistry of these ligands was examined by potentiometric and spectrophotometric methods in combination with 1H NMR spectroscopy. The respective pFeIII values showed a cooperative effect of the mixed chelating units. Moreover, the pFeIII dependence on pH showed that the mixed ligands exhibit a higher complexing ability than the parent ligands over the pH range 5,9 which is of biological relevance. This result could be of great interest for medical applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Photoinduced Energy- and Electron-Transfer Processes in Dinuclear RuII,OsII, RuII,OsIII, and RuIII,OsII Trisbipyridine Complexes Containing a Shape-Persistent Macrocyclic Spacer

CHEMPHYSCHEM, Issue 1 2006
Margherita Venturi Prof.
Abstract The PF6,salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2,-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the RuIIunit is almost completely quenched with concomitant sensitization of the emission of the OsIIunit. Electronic energy transfer from the RuIIto the OsIIunit takes place by two distinct processes (ken=2.0×108and 2.2×107s,1at 298 K). Oxidation of the OsIIunit of [(bpy)2Ru(1)Os (bpy)2]4+by CeIVor nitric acid leads quantitatively to the [(bpy)2RuII(1)OsIII(bpy)2]5+complex which exhibits a bpy-to-OsIIIcharge-transfer band at 720 nm (,max=250,M,1cm,1). Light excitation of the RuIIunit of [(bpy)2RuII(1)OsIII(bpy)2]5+is followed by electron transfer from the RuIIto the OsIIIunit (kel,f=1.6×108and 2.7×107s,1), resulting in the transient formation of the [(bpy)2RuIII(1)OsII(bpy)2]5+complex. The latter species relaxes to the [(bpy)2RuII(1)OsIII(bpy)2]5+one by back electron transfer (kel,b=9.1×107and 1.2×107s,1). The biexponential decays of the [(bpy)2*RuII(1)OsII(bpy)2]4+, [(bpy)2*RuII(1)OsIII(bpy)2]5+, and [(bpy)2RuIII(1)OsII(bpy)2]5+species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru,Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge. [source]