Showing papers on "Ring-opening metathesis polymerisation published in 1981"

Olefin metathesis over well-defined active fixed molybdenum catalysts. Structure and oxidation state of the active site and reaction mechanism

Abstract: Fixed Mo catalysts (supported molecular catalysts), synthesised using the facile reaction between Mo (π-C3H5)4 and the surface acidic OH groups of alumina, silica and silica–alumina, were found to be very active for propene and but-1-ene metathesis in the temperature range 268–308 K. The isolated and coordinatively unsaturated Mo4+ species which are chemically bonded to the support surface are the active species. The nature of the ligands and supports coordinated to the Mo4+ ions produce different catalytic activities and selectivities. The support also works as a reservoir/supplier of reactants. Metathesis on fixed Mo catalysts is explained by a one-site chain mechanism involving carbene intermediates.

Structures of rhenium(VII) oxides on alumina and their catalytic activities for metathesis of olefins.

Abstract: IR studies revealed that the Re2O7/Al2O3 metathesis catalyst has two different surface rhenium species, [ReO4]ads− and [Re2O7]ads, which are similar in both structure and behavior to those in the aqueous solution of Re2O7. [Re2O7]ads, which is present only in high loading catalysts, should be responsible for their high catalytic activity for the metathesis of olefins.

Role of dioxygen as an activator in olefin metathesis

Abstract: Evidence is presented that the beneficial or essential influences often noted when small amounts of dioxygen are added to catalytic systems for olefin metathesis and ring-opening polymerization are due to the formation of epoxides and the corresponding metalla-oxacyclobutanes,[[graphic omitted]R1; fission of the latter affords initiating metallacarbenes but isomerization and dimerization of the epoxide via this metallacycle are the major reaction pathways.

The Characterization of a Novel Metathesis Catalyst, β-Titanium Oxide-supported Molybdenum Oxide

Abstract: The results of the X-ray photoelectron spectroscopy of a novel metathesis catalyst, MoOx/β-TiO2, are discussed with reference to its catalytic behavior. It is concluded that the active center for the metathesis reaction of olefin is the molybdenum ion with an oxidation higher than +4 on the average, and that the hydrogen scrambling of olefin during the metathesis is caused by the OH group on the TiO2 surface. During the preparation of this catalyst, the decomposition of titanic acid to TiO2 is found to be accelerated by MoO3; a similar thing can be seen of the reduction of MoO3 to zero-valent molybdenum by TiO2.

Process for the preparation of linear olefins from triethylaluminum and tripropylaluminum via growth, isomerization and metathesis

Abstract: Internal olefins are subjected to metathesis closely coupled after an isomerization reaction to obtain desired molecular weight range linear olefins. Specific process steps and separation conditions are necessary to obtain the desired linear olefins.

Olefin Metathesis Reaction Over Supported Molybdenum Oxide Catalysts

Abstract: Metathesis reaction of a mixture of normal and deuterated olefin has been carried out on a novel molybdenum oxide catalyst, on which neither hydrogen scrambling nor isomerization of olefins took place. On the basis of the experimental results obtained on this catalyst, detailed mechanism of the metathesis reaction, especially the direct formation of metal carbenes on solid surface, has been proposed. Various metal oxides were examined as support of molybdenum oxide with respect to the catalytic activity, selectivity and hydrogen scrambling and the state of molybdenum ion on these supports has been examined by X-ray photoelectron spectroscopy. It was found that the state of molybdenum ion on the catalyst surface was strongly affected by the sort of support and was supposed that well dispersed Mo 4+ and/or Mo 5+ with some particular coordination of oxygen atoms is the active center for metathesis reaction.

Metathesis of dialkenylsilanes and polymerization of 1,1-dimethyl-1-sila-3-cyclopentene in presence of aluminum-rhenium catalysts

Abstract: 1. It was shown that the efficient metathesis of dialkenylsilanes of variable structure in the presence of aluminum-rhenium catalysts is possible. 2. Conditions were found for the preparative synthesis of 4,9-disila-4,4,9,9-tetramethy1-1,6,11-dodecatriene and 1,1-dimethyl-1-sila-3-cyclohexene via the inter- and intramolecular metathesis reaction. 3. 1,1-Dimethyl-1-sila-3-cyclopentene polymerizes to a linear polysilapentenomer in the presence of Al-Re catalysts.

Hydrogen exchange, isomerization, hydrogenation and metathesis of olefins on solid surfaces：unsaturated coordination model of active sites

Abstract: A review is given on the results ever obtained III the author's laboratory with olefin reactions over nickel, sulfided nickel, molybdenum disulfide and titania-supported molybdenum oxide catalysts. Some detailed discussions are given on the stereoselectivity observed in [D41-2-butene formation by metathesis of a [Dol/[D81 (1: 1) mixture of cis or trans2-butene, and it is suggested by the extended HUckel theory (EHT) calculation that this stereoslectivity may be caused by the restricted orientation of C 2-carbene and metallacyclobutane intermediates on surface molybdenum ion surrounded by lattice oxygen. Taking account of the results obtained by X-ray photoelectron spectroscopy of the catalyst, it is emphasized that specially unsaturated coordination of legands (e.g. sulfur, oxygen etc.) to central metal ion is essential for an active site for the selective catalyses over these solid surfaces.

Formation of cyclopropane in the reaction of the components of complex metathesis catalyst

Abstract: 1. Cyclopropane (the product from the reaction of the carbene with the olefin) is formed in the reaction of the components of the metathesis catalyst having the composition MoCl3(C17H35COO)2-Al(C2H5)2Cl. 2. Cyclopropane is not formed in the presence of cyclopentene and vinyltrimethylsilane, which trap the carbene active centers.