Search results for "metathesis"

New practical tungsten(VI) based catalyst systems for ring opening metathesis polymerisation

2002

Abstract Tungsten(VI) complexes of the type trans -[WCl 2 (diol)(OAr) 2 ] were studied as catalyst precursors for ROMP of norbornene and dicyclopentadiene. These compounds form active catalysts when treated by simple Grignard reagents, such as methyl magnesium iodide or neophyl magnesium chloride. Moreover, polymerisations can be run under ambient atmosphere without complicated inert atmosphere techniques.

End Capping Ring-Opening Olefin Metathesis Polymerization Polymers with Vinyl Lactones

2008

The selective placement of a functional group at the chain end of a ring-opening metathesis polymer using ruthenium carbene initiators has been a significant limitation. Here we demonstrate a highly effective and facile end-capping technique for ROMP with living ruthenium carbene chain ends using single-turnover olefin metathesis substrates. Vinylene carbonate and 3H-furanone are introduced as functionalization and termination agents for the ruthenium-initiated ring-opening metathesis polymerization. This leads directly to the formation of functional polymer end groups without further chemical transformation steps. Aldehyde and carboxylic acid end groups can be introduced by this new method…

Eine apparatur zur gaschromatographischen verfolgung der metathesereaktion kurzkettiger olefine

1973

Es wird eine Apparatur beschrieben, die einen Reaktor, kombiniert mit einem Gaschromatographen, umfast und die es gestattet, Umsetzungen kurzkettiger Olefine bei der Metathesereaktion schnell und einfach zu erfassen. Die Leistungsfahigkeit der Apparatur wird u. a. am Beispiel der Metathesereaktion von Penten-2 in Gegenwart des Katalysator-systems WCl6/C2H5OH/(C2H5)3Al2Cl3 demonstriert. An apparatus consisting of a reactor tube in conjunction with a gaschromatograph is described which allows to follow instantaneously the progress of the metathesis reaction of short chain olefins. The ability of the apparatus is demonstrated among other things by means of the metathesis reaction of pentene-2 …

An All-ROMP Route to Graft Copolymers

2007

A new versatile synthesis strategy for macromonomers has been developed that uses the living ring-opening metathesis polymerization (ROMP) with commercial Grubbs first generation ruthenium initiators. Homopolymers as well as diblock copolymers were end-functionalized with norbornene derivatives to serve as macromonomers. The graft copolymerization of the macromonomers was also carried out employing ROMP. Well-defined and highly functional graft copolymers are accessible by this new synthetic route.

Synthesis of huge macrocycles using two calix[4]arenes as templates.

2005

Macrocycles with up to 100 atoms have been synthesised using two calix[4]arenes as templates: first, (3,5-dialkenyloxy)phenyl groups are attached to the wide rim of a calix[4]arene via urea links, then the alkenyl groups are connected via a metathesis reaction using a tetratosylurea calix[4]arene for their correct prearrangement and finally the urea functions are cleaved to detach the newly formed macrocycles.

Calix[4]arene-Based Bis[2]catenanes: Synthesis and Chiral Resolution

2007

The exclusive formation of hydrogen-bonded dimers between tetraaryl and tetratosylurea calix[4]arenes has been used to prepare a series of ten "bisloop" tetraurea calix[4]arenes 3, in which adjacent phenylurea groups are covalently linked through alpha,omega-dioxyalkane chains. This dimerization with tetratosylurea 2 as template preorganizes the alkenyl residues of tetra(m-alkenyloxyphenyl) ureas 1 and enables their selective connection in high yield (up to 95 %) by olefin metathesis followed by hydrogenation. The "bisloop" calixarenes 3 also exclusively form heterodimers with 1. Thus, in a separated metathesis/hydrogenation sequence, a series of 14 cyclic bis[2]catenanes 4, in which two ca…

Tungsten(VI) complexes with aminobis(phenolato) [O,N,O] donor ligands.

2004

The reaction between trisdiolatotungsten(VI) complex [W(eg)(3)] (1) (eg = 1,2-ethanediolato dianion) and phenolic ligand precursor methylamino-N,N-bis(2-methylene-4,6-dimethylphenol) (H(2)L(Me)) or methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol) (H(2)L(tBu)) affords monomeric oxotungsten complex [WO(eg)(L(Me))] (2) or [WO(eg)(L(tBu))] (3), respectively. These complexes react further with chlorinating reagents, which leads to the displacement of ethanediolato ligands from the complex units and formation of cis and trans isomers of the corresponding dichloro complexes [WOCl(2)(L(Me))] (4) and [WOCl(2)(L(tBu))] (5), respectively. Identical dichloro complexes were also prepared by …

Fourfold [2]rotaxanes of calix[4]arenes by ring closure.

2006

Gold(I)-Mediated Silicon-Silicon Bond Metathesis at Room Temperature

2010

Enantioselective synthesis of fluorinated alpha-amino acids and derivatives in combination with ring-closing metathesis: intramolecular pi-stacking i…

2001

[reaction: see text]. Hydride reduction of C=N bonds stereocontrolled by intramolecular pi-stacking interactions of 1-naphthylsulfinyl and N-aryl groups, nonoxidative Pummerer rearrangement, and ring-closing metathesis are efficiently combined in a highly stereoselective entry to enantiomerically pure cyclic and acyclic fluorinated beta-amino alcohols and alpha-amino acid derivatives, respectively.