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Ruthenium Carbene Complex (ruthenium + carbene_complex)

Distribution by Scientific Domains

Chemistry	83%

Selected Abstracts

Lewis Acid Assisted Cross Metathesis of Acrylonitrile with Functionalized Olefins Catalyzed by Phosphine-Free Ruthenium Carbene Complex.

CHEMINFORM, Issue 11 2006
Chen-Xi Bai
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

An Ionic Liquid-Tagged Second Generation Hoveyda,Grubbs, Ruthenium Carbene Complex as Highly Reactive and Recyclable Catalyst for Ring-Closing Metathesis of Di-, Tri- and Tetrasubstituted Dienes.

CHEMINFORM, Issue 45 2005
Qingwei Yao
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Ring-Closing Olefin Metathesis on Ruthenium Carbene Complexes: Model DFT Study of Stereochemistry

CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2005
Sergei F. Vyboishchikov Dr.
Abstract Ring-closing metathesis (RCM) is the key step in a recently reported synthesis of salicylihalamide and related model compounds. Experimentally, the stereochemistry of the resulting cycloolefin (cis/trans) depends strongly on the substituents that are present in the diene substrate. To gain insight into the factors that govern the observed stereochemistry, density functional theory (DFT) calculations have been carried out for a simplified dichloro(2-propylidene)(imidazole-2-ylidene)ruthenium catalyst I, as well as for the real catalyst II with two mesityl substituents on the imidazole ring. Four model substrates are considered, which are closely related to the systems studied experimentally, and in each case, two pathways A and B are possible since the RCM reaction can be initiated by coordination of either of the two diene double bonds to the metal center. The first metathesis yields a carbene intermediate, which can then undergo a second metathesis by ring closure, metallacycle formation, and metallacycle cleavage to give the final cycloolefin complex. According to the DFT calculations, the stereochemistry is always determined in the second metathesis reaction, but the rate-determining step may be different for different catalysts, substrates, and pathways. The ancillary N-heterocyclic carbene ligand lies in the Ru-Cl-Cl plane in the simplified catalyst I, but is perpendicular to it in the real catalyst II, and this affects the relative energies of the relevant intermediates and transition states. Likewise, the introduction of methyl substituents in the diene substrates influences these relative energies appreciably. Good agreement with the experimentally observed stereochemistry is only found when using the real catalyst II and the largest model substrates in the DFT calculations. [source]

Synthesis of a norbornene monomer having cyclic carbonate moiety based on CO2 fixation and its transition metal-catalyzed polymerizations

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010
Atsushi Sudo
Abstract A norbornene monomer bearing cyclic carbonate moiety (NB-CC) was successfully synthesized from the corresponding precursor having epoxy moiety by its reaction with carbon dioxide under atmospheric pressure, which was efficiently catalyzed by lithium bromide. NB-CC underwent the ring-opening metathesis polymerization (ROMP) catalyzed by a ruthenium carbene complex to give the corresponding poly(norbornene), of which side chain inherited the cyclic carbonate moiety from the monomer without any deterioration. The same ROMP system was applicable to the copolymerization of NB-CC and 5-butyl-2-norbornene (BNB), which afforded the corresponding copolymer with a composition ratio same as a feed ratio. In addition, by using a catalytic system consisted of palladium (II) acetate/tricyclohexylphosphine/triphenylcarbenium tetrakis(pentafluorophenyl)borate, the copolymerization of NB-CC and BNC proceeded successfully in a vinyl addition polymerization mode to give the corresponding poly(norbornene) having CC moiety in the side chain. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3896,3902, 2010 [source]

On the Rigidity of Polynorbornenes with Dipolar Pendant Groups

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2006
Wei-Yu Lin
Abstract A range of polynorbornenes (PNBs) with fused dipolar pendant groups at C-5,6 positions was synthesized by ring-opening metathesis polymerization catalyzed by a ruthenium carbene complex (Grubbs I). Photophysical studies, EFISH measurements, and atomic force microscopy images have been used to investigate the structures and morphology of these polymers. These results suggest that the polymers may adopt rigid rod-like structures. The presence of the double bonds in PNBs appeared to be indispensable for the rigidity of the polymers. Interaction between unsaturated pendant groups may result in coherent alignment leading to a rod-like structure. [source]

Ligand Influence on Metathesis Activity of Ruthenium Carbene Catalysts: A DFT Study

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2007
Bernd
Abstract A survey of the concept of active and inactive ligand conformations in ruthenium alkene carbene complexes of the Grubbs catalyst type is presented. This concept is extended to a variety of anionic ligand atoms. Density functional theory calculations at the B3LYP/LACV3P**+//B3LYP/LACVP* level of theory were performed on the precatalyst, 14 valence-electron intermediate, alkene carbene conformers and ruthena(IV)cyclobutane model intermediates for several ligands, such as methoxide, methanethiolate, fluoride, mesylate, water, and ammonia. The rule of the superiority of metathesis catalysts with small and electron-withdrawing halogens does not apply to fluoride ligands. Alkoxides and thiolates also destabilize active carbene conformations, while mesylate ligands lead to a balanced energetic relation of active and inactive carbene orientations. Cationic ruthenium carbene species with aqua or ammine ligands are limited by unfavored ligand dissociation to 14 valence-electron intermediates. A guideline for the design of novel ligand systems for ruthenium carbene complexes as metathesis catalysts is proposed. [source]