Alkoxide Ligands Research Articles

Quadruple bonds between molybdenum atoms supported by alkoxide ligands. Structural effects and reactivity patterns

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTQuadruple bonds between molybdenum atoms supported by alkoxide ligands. Structural effects and reactivity patternsMalcolm H. Chisholm, Kirsten Folting, John C. Huffman, and Robert J. TatzCite this: J. Am. Chem. Soc. 1984, 106, 4, 1153–1154Publication Date (Print):February 1, 1984Publication History Published online1 May 2002Published inissue 1 February 1984https://doi.org/10.1021/ja00316a076RIGHTS & PERMISSIONSArticle Views177Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (283 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Metal-metal bonds and metal-carbon bonds in the chemistry of molybdenum and tungsten alkoxides

Abstract : Metal-metal bonds are found in alkoxides of molybdenum and tungsten when the metal atoms are in oxidation states 2 through 5. Metal-metal bonds may be locailized and multiple or single in order, or may be delocalized in cluster molecular orbitals. The structures of these metal alkoxides are quite different from those seen previously. Metal-metal bonds provide a reservoir of electrons for redox reactions: the reservoir may be tapped in oxidative- addition reactions and filled in reductive-eliminatin reactions. Alkoxide ligands may act as four or two electron donor ligands and may readily change between terminal and bridging sites. This allows for the facile interconnversion of saturated and unsaturated metal centers. As strong Pi-donor ligands, they can enhance backbonding to pi-acid ligands on the same metal. By pi-donating to vacant metal d orbitals, they may suppress metal-hydride abstraction from coordinated alkyl, alkylidene and alkylidyne ligands and they stabilize metals in high oxidation states. A variety of steric control can be engineered by choice of alkyl (RO0 groups and this may greatly influence structure, M-M bonding and reactivity of coordinated ligands.

Alkoxides of molybdenum and tungsten: metal—metal bonds and organometallic chemistry

Recent developments in the chemistry of alkoxides of molybdenum and tungsten are described. Two aspects of particular emphasis are (i) metal—metal bonds and (ii) the potential role of alkoxide ligands in organometallic chemistry.

One-electron reduction of ferriporphyrins and reactions of ferric and ferrous porphyrins with a halothane-derived radical

The reduction of ferrideuteroporphyrin by ..cap alpha..-hydroxyisopropyl radicals is investigated in acidic 2-propanol and acidic 2-propanol-water mixtures by means of steady-state and pulse radiolysis. The rate constant of the reaction is much higher (k approx. = 1.3 x 10/sup 9/ M/sup -1/s/sup -1/) than that reported for neutral solutions emphasizing the effect of the positive charge carried by the ferric porphyrin in acidic solutions (due to protonation of the alkoxide ligand). Competition kinetic experiments using p-nitroacetophenone as a referene solute show that ..cap alpha..-hydroxyisopropyl radicals are readily scavenged by halothane (CF/sub 3/CHClBr), leading to CF/sub 3/CHCl radicals. Pulse irradiation of ferriporphyrin solutions containing halothane allows investigation of the reaction of CF/sub 3/CHCl radicals with either ferric or ferrous prophyrins depending on the halothane concentration. No reaction of CF/sub 3/CHCl radicals with ferriporphyrin can be detected (k less than or equal to 10/sup 6/ M/sup -1/ s/sup -1/). On the other hand, a nearly diffusion-controlled reaction is observed between CF/sub 3/CHCl radicals and ferrous porphyrin leading to the sigma-bonded alkyl complex of the ferric porphyrin (PFe/sup III/CF/sub 3/CHCl, where CF/sub 3/CHCl stands for the alkyl anion). These results are discussed with regard to the reactivity of other alkyl radicals. The relevancemore » to biological models of toxicity of halothane (a widely used anesthetic agent) is outlined.« less

Ligand redistribution and carbonyl insertion: The effect of competitive π-donation

Electron deficient CpTiCl 3 reacts with the bis-alkoxide CpCl TiOCMe 2CMe 2O to produce the diolato dimer (CpTiCl 2)OCMe 2CMe 2O(TiCl 2Cp). CpTiCl 3 reacts with Cp 4Ti 4Cl 4(μ 2-O) 4, which also has two oxo ligands on each titanium atom, to produce [CpTiCl 2] 2O. These and other redistribution reactions indicate that destabilization results from internal competition for metal d-orbitals by strong π-donor (e.g. alkoxide) ligands. Equilibrium constants for the formation of the η 2-acetyl complexes Cp 2Zr[C(O)Me]X by Co insertion into Cp 2ZrMeX decrease in the order X = Me>Cl>OEt. This reflects internal competition of π-donor orbitals on X with the oxygen donor orbital in the η 2-acetyl functionally. The significance of this effect for Fischer-Tropsch syntheses in both homogeneouus and heterogeneous media is discussed.

Ligandenfeldspektroskopische Untersuchungen an Übergangsmetall -Aluminium -Tetraalkoxiden / Ligand Field Spectroscopic Studies of Transition Metal Aluminium-Tetraalkoxides

Abstract The preparation and the electronic spectral properties of compounds M[Al(OR)4]2 (M = Co, Ni, Cu and R = CH3, C2H5, n-C3H7, n-C4H9) are described. The spectral data are used in conjunction with ligand field theory in deducing the structures of the compounds. The spectrum of green Ni[Al(OR)4]2 is interpreted as a Ni(OR)6 octahedron sharing faces with two Al(OR)4 tetrahedrons. It is proposed that Co 2+ and Cu 2+ are in a distorted octahedral coordination. The alkoxide ligands have been fitted into the spectrochemical and the nephelauxetic series. They are close to H2O in this series.

The catalytic activity of AlTi complexes as a function of the electron donating capacity of alkoxide ligands

Polymerization of ethylene has been investigated in the presence of 20 AlTi catalytic complexes having differing structures and numbers of RO-donor ligands. The reaction kinetics were analysed at constant monomer concentration. A kinetic scheme is suggested and equations have been arrived at which permit a full quantitative characterization of the activity of the investigated catalyst complexes for the ethylene polymerization in the shape of elementary reactions. The concentration of reactive centres has been estimated for all the systems. The results of the influence of the donor ligands on the catalyst activity in the polymerizations of olefines are reported and proof is given for the fact that the electron donating capacity increase of the ligands increases only the rate constant of chain propagation while the overall catalytic activity will drop.