24949-38-0Relevant articles and documents
Improved metathesis lifetime: Chelating pyridinyl-alcoholato ligands in the second generation grubbs precatalyst
Du Toit, Jean I.,Jordaan, Margaritha,Huijsmans, Carlijn A. A.,Jordaan, Johannes H. L.,Van Sittert, Cornelia G. C. E.,Vosloo, Hermanus C. M.
, p. 5522 - 5537 (2014/06/10)
Hemilabile ligands can release a free coordination site "on demand" of an incoming nucleophilic substrate while occupying it otherwise. This is believed to increase the thermal stability and activity of catalytic systems and therefore prevent decomposition via free coordination sites. In this investigation chelating pyridinyl-alcoholato ligands were identified as possible hemilabile ligands for incorporation into the second generation Grubbs precatalyst. The O,N-alcoholato ligands with different steric bulk could be successfully incorporated into the precatalysts. The incorporation of the sterically hindered, hemilabile O,N-ligands improved the thermal stability, activity, selectivity and lifetime of these complexes towards the metathesis of 1-octene. A decrease in the activity of the second generation Grubbs precatalyst was additionally observed after incorporating a hemilabile O,N-ligand with two phenyl groups into the system, while increasing their lifetime.
The metathesis of α-olefins over supported Re-catalysts in supercritical CO2
Selva, Maurizio,Perosa, Alvise,Fabris, Massimo,Canton, Patrizia
experimental part, p. 229 - 238 (2010/04/22)
At 35 °C, in the presence of supercritical carbon dioxide (80-150 bar) as a solvent, α-olefins (RCHCH2, R = C4-C6) undergo highly selective self-metathesis catalyzed by supported Re-oxide (7%). To the best of our knowledge, this is the first procedure for the metathesis of alkenes, in which heterogeneous catalysts are combined with the use of dense CO2. The intrinsic eco-compatibility and the unique physicochemical properties of this medium offer both environmental and synthetic advantages: not only conventional toxic solvents (e.g. n-heptane and toluene) can be replaced, but the reaction is faster. For instance, after 2 h, the average conversion of 1-octene is 67% and 40% in scCO2 and n-heptane, respectively. The product of self-methatesis, 7-tetradecene, can be isolated in yields up to 68%. At 90 bar, the reaction is rather sensitive to the mole fraction of the olefin (in scCO2); though, the enhancement of the pressure (and the density) of the supercritical medium does not induce significant effects on either the rate or the selectivity of the process. The nature of the catalytic support also greatly affects the reaction outcome: Re-oxide shows good activity if dispersed over γ-Al2O3, while silica-based systems are ineffective.
Ruthenium catalyst with a chelating pyridinyl-alcoholato ligand for application in linear alkene metathesis
Jordaan, Margaritha,Vosloo, H. C. Manie
, p. 184 - 192 (2008/02/03)
The catalytic activity of ruthenium alkylidene complexes [RuCl(LX(ON)(=CHPh)] [L = H2IMes and PCy3, ON = 1-(2′-pyridinyl)cyclohexan-1-olate)], bearing a chelating pyridinyl-alcoholate ligand, was investigated for the metathesis of 1-octene in the absence of a solvent. Both systems were active for the metathesis of 1-octene yielding trans-7-tetradecene and ethene as the primary metathesis products. Although the activity of both systems increased with an increase in reaction temperature, the activity of [RuCl(H2IMes)(ON)(=CHPh)] started to decrease at temperatures above 70°C, with a simultaneous exponential increase in the secondary metathesis products due to double-bond isomerisation of the substrate. Although the initiation rates for these systems are slower compared to Grubbs 1 and Grubbs 2 for the metathesis of 1-octene at 60°C, they have a higher activity and longer lifetime.
AIR-STABLE BINUCLEAR ALKOXYTUNGSTEN COMPLEXES AS CATALYST PRECURSORS FOR OLEFIN METATHESIS
Savard, Jacques,Alper, Howard
, p. 2483 - 2486 (2007/10/02)
The use of the air-stable complexes tetrachlorobis(μ-methoxy)bis(methanolo)dimethoxyditungsten (1) and tetrachlorobis(μ-ethoxy)tetraethoxyditungsten (2) as catalyst precursors for the metathesis of 1-octene is described.Using mild conditions, the latter was converted to 7-tetradecene (4) in fair yields when diethylaluminum chloride (3) was used as a cocatalyst.Product stereoselectivity was 4/1 in favor of the trans isomer.The reaction was also shown to be efficient for the production of 2-nonenes.
Untersuchungen von Polymerisation- und Metathese-Reaktionen XIV. Darstellung heterogener, bimetallischer Metathese-Katalysatoren durch Reaktionen von Carbin-Wolfram-Komplexen des Fischer-Typs mit reduziertem Phillips-Katalysator
Weiss, Karin,Denzner, Michael
, p. 273 - 280 (2007/10/02)
Reactions of Fischer-type carbyne tungsten complexes X(CO)nWCPh (X=Cl, Br, I, n=4; X=Cp, n=2) with reduced Phillips catalyst, a chromium(II) compound surface-bound to silica, yield heterogeneous bimetallic metathesis catalysts for alkenes.The reactions probably proceed via a cycloaddition of the WC-carbyne bond with the chromium(II) atoms to give dimetallacyclopropene derivatives.The bimetallic catalysts formed by reaction with the halogeno substituted carbyne complexes are very active alkene metathesis catalysts, as demonstrated by the reaction with 1-octene.The original polymerisation activity towards 1-alkenes of the surface-bound chromium(II) atoms disappeared after reaction with carbyne complexes.
