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Oxo Complexes (oxo + complex)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Incorporation of a (Cyclopentadienyl)molybdenum Oxo Complex in MCM-41 and Its Use as a Catalyst for Olefin Epoxidation

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2004
Marta Abrantes
Abstract The tricarbonyl complex [(,5 -C5H4 -COOMe)Mo(CO)3Cl] was prepared from the reaction of sodium (methoxycarbonyl)cyclopentadienide, (C5H4 -CO2Me)Na, with (Bu4N)[Mo(CO)5I]. Heating the ester with 3-(triethoxysilyl)propylamine gave the amide derivative {[,5 -C5H4 -CONH-C3H6Si(OEt)3]Mo(CO)3Cl}. The functionalised tricarbonyl complex was immobilised in the ordered mesoporous silica MCM-41 with a loading of 13 wt.-% Mo (1.4 mmol·g,1) by carrying out a grafting reaction in dichloromethane. Powder X-ray diffraction and nitrogen adsorption,desorption analysis indicated that the structural integrity of the support was preserved during the grafting and that the channels remained accessible, despite significant reductions in surface area, pore volume and pore size. The success of the coupling reaction was confirmed by 29Si and 13C (CP) MAS NMR spectroscopy. A supported dioxo complex of the type [(,5 -C5H4R)MoO2Cl] was subsequently prepared by oxidative decarbonylation of the tethered tricarbonyl complex using tert -butyl hydroperoxide (TBHP). The oxidised material is an active catalyst for the liquid phase epoxidation of cyclooctene with TBHP as the oxygen source. Similar catalytic results were obtained using the tethered tricarbonyl complex directly as a pre-catalyst since fast oxidative decarbonylation occurs under the reaction conditions used. For both systems, the desired epoxide was the only product and the initial activities were about 13 mol·molMo,1·h,1. The solid catalysts were recycled several times. Some activity was lost between the first and second runs but thereafter tended to stabilise. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Analysis of Reaction Channels for Alkane Hydroxylation by Nonheme Iron(IV),Oxo Complexes,

ANGEWANDTE CHEMIE, Issue 33 2010
Caiyun Geng
Neue High-Spin-Pfade: Die vier plausiblen Reaktionspfade der Alkanhydroxylierung durch Nichthäm-Eisen(IV)-Oxo-Komplexe wurden rechnerisch untersucht. Der Triplett-,-Pfad ist energetisch zu hoch, um an einer C-H-Aktivierung beteiligt zu sein , jedoch konkurriert die Reaktivität des Quintett-,-Kanals mit dem Triplett-Pfad, was einen neuen Ansatz für die spezifische C-H-Aktivierung durch Eisen(IV)-Oxo-Spezies bieten könnte (siehe Schema). [source]

Rhenium(VII) Oxo Complexes as Extremely Active Catalysts in the Dehydration of Primary Amides and Aldoximes to Nitriles.

CHEMINFORM, Issue 51 2002
Kazuaki Ishihara
No abstract is available for this article. [source]

UIII -Induced Reductive Co-Coupling of NO and CO to Form UIV Cyanate and Oxo Derivates

CHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2010
Alistair S.
CO and NO give NCO and O! Sequential treatment of [U(,-C8H6{SiiPr3 -1,4}2)(,-Cp*)] with CO followed by NO (or vice versa) affords a mixture of the bridging cyanate complex [{U(,-C8H6{SiiPr3 -1,4}2)(,-Cp*)}2(,-OCN)2] and the bridging oxo complex [{U(,-C8H6{SiiPr3 -1,4}2)(,-Cp*)}2(,-O)], both of which have been structurally characterised (see scheme). [source]

Two oxo complexes with tetra­nuclear [Fe4(,3 -O)2]8+ and trinuclear [Fe3(,3 -O)]7+ units

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2006
Ana María Atria
Two new oxo complexes, namely hexa-,2 -acetato-acetato­aquabis­(di-3-pyridylamine)di-,3 -oxo-tetra­iron(III) chloride mono­hydrate ethanol 1.25-solvate, [Fe4(C2H3O2)7O2(C10H9N3)2(H2O)]Cl·1.25C2H6O·H2O, (I), containing a tetra­nuclear [Fe4(,3 -O)2]8+ unit, and 2-methyl­imidazolium hexa-,2 -acetato-acetatodiaqua-,3 -oxo-triiron(III) chloride dihydrate, (C4H7N2)[Fe3(C2H3O2)7O(H2O)2]Cl·2H2O, (II), with a trinuclear [Fe3(,3 -O)]7+ unit, are presented. Both structures are formed by two well differentiated entities, viz. a compact isolated cluster composed of FeIII ions coordinated to O2, and CH3CO2, anions, and an external group formed by a central Cl, ion surrounded by different solvent groups to which the anion is bound through hydrogen bonding. In the case of (I), charge balance cannot be achieved within the groups, so the structure is macroscopically ionic; in the case of (II), in contrast, each group is locally neutral owing to the inter­nal compensation of charges. The trinuclear complex crystallizes with the metal cluster, chloride anion and 2-methyl­imidazolium cation bisected by a crystallographic mirror plane. [source]

Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to ,-Oxodiiron(III) Complexes and Effect of ,-Fluorination on the Reaction Kinetics

CHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2008
Nasser
Abstract We have synthesized the mono, di-, and tri-,-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F2TPA and F3TPA, respectively. Fluorination at the ,-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45,70,mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F2TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl2. All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable ,-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three ,-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the ,4N coordination mode. With FTPA, the compound is a neutral ,-oxodiiron(III) complex with a ,3N coordination mode of the ligand. Oxygenation of the F2TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all ,-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of ,-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90,% conversion over 40,h, the monofluorinated ligand provides a complex that has fully reacted after 30,h, whereas the reaction time for the complex with the difluorinated ligand is only 10,h. Analysis of the spectroscopic data reveals that formation of the ,-oxo complexes proceeds in two distinct reversible kinetic steps with k1,10,k2. For TPAFeCl2 and FTPAFeCl2 only small variations in the k1 and k2 values are observed. By contrast, F2TPAFeCl2 exhibits k1 and k2 values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of ,-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials. [source]