From the reaction of metal—carbene complexes with cyclic enol ethers to the synthesis and structure of μ-alkylidene complexes of tungsten and their possible implication in the olefin metathesis reaction
TL;DR: The reaction of a metathesis catalyst prepared from W(CO) 6 /CCl 4 /hν with cyclic enol ethers gives products arising from the probable insertion of a dichlorocarbene complex of tungsten into the carbon-carbon double bond.
About: This article is published in Journal of Molecular Catalysis.The article was published on 1980-05-01. It has received 22 citations till now. The article focuses on the topics: Ring-opening polymerization & Enol.
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01 Jan 1991
TL;DR: The chemistry of transition metal carbene complexes has been examined with an eye to applications in organic synthesis ever since their discovery by Fischer in 1964, and the growth in the number of useful applications has been exponential with time.
Abstract: The chemistry of transition metal carbene complexes has been examined with an eye to applications in organic synthesis ever since their discovery by Fischer in 1964, and the growth in the number of useful applications has been exponential with time.1–3 There are two types of transition metal carbene complexes; those which have electrophilic carbene carbons and which are typified by the pentacarbonylchromium complex (1), and those which have nucleophilic carbene carbons and which are typified by the biscyclopentadienyltitanium complex (2). Complexes (1) and (2) are often referred to as ‘carbene’ and ‘alkylidene’ complexes, respectively. This review will be limited to the chemistry of electrophilic carbene complexes of the Fischer type. The chemistry of the nucleophilic alkylidene complexes will be covered in Chapter 9.3, this volume.4
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74 citations
TL;DR: The hypothesis that metals (other than ruthenium) must be in their highest oxidation states for their carbene derivatives to initiate olefin metatheses legitimizes the uniqueness of high-oxidation-state molybdenum and tungsten carbenes as effective initiators, and it means that the Fischer tungsteins that even earlier were found to initiateOlefin meetingatheses and related transformations must be oxidized before they can be effective.
Abstract: Experiments carried out 24 years ago with tantalum carbenes have led to the much cited hypothesis that metals (other than ruthenium) must be in their highest oxidation states for their carbene derivatives to initiate olefin metatheses. The hypothesis legitimizes the uniqueness of high-oxidation-state molybdenum and tungsten carbenes as effective initiators, and it means that the Fischer tungsten carbenes that even earlier were found to initiate olefin metatheses and related transformations must be oxidized before they can be effective. The newer initiators have been termed "well-defined", the older "ill-defined". But what does the evidence show?
64 citations
31 citations
TL;DR: In this paper, an optimization study of W(CO) 6 CBr 4 / hv is presented, where the active species are characterised by reaction with acetophenone and copolymers of phenylacetylene and norbornene.
Abstract: Metathesis polymerisation can be effected with many catalysts under a variety of conditions. The system described here, viz., W(CO) 6 CBr 4 / hv , induces polymerisation by in situ generation of the active species and has not been reported in the literature so far. In this paper, optimisation studies of this system, yields obtained with various monomers and characterisation of the active species are discussed. Variation of different parameters such as the ratio of W(CO) 6 :CBr 4 , the time of photolysis and the effect of solvents as well as that of the metal carbonyls have been studied. In addition, copolymers of phenylacetylene and norbornene have been synthesised. We have also attempted to characterise the active species responsible for the polymerisation by reaction with acetophenone.
19 citations
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TL;DR: On propose un schema reactionnel en accord avec les faits observes dans la reaction de disproportion des olefines acycliques, la polymerisation des ollines cycliques, the telomerisation of l'olefine cyclique, and the polymerisation of olline cycliques by les olefine acyCLiques as discussed by the authors.
Abstract: La co-reaction des olefines cycliques avec les olefines acycliques en presence des systemes WOCl4/Al(C2H5)2Cl et WOCl4/Sn(C4H9)4 conduit a une telomerisation de l'olefine cyclique; aux extremites des molecules de telomere sont fixes deux groupements, identiques ou differents, issus de l'olefine acyclique par une reaction non consecutive.
Ont ete plus particulierement etudies: le cyclopentene et le cyclooctene d'une part, le pentene-2, le pentene-1, le butene-2 et le propylene d'autre part.
Le cyclooctadiene-1.5 et le cyclododecatriene-1.5.9 reagissent avec le pentene-2, par reaction non consecutive, en tant que reste CHCH2CH2CH.
La repartition des telomeres obeit a une loi statistique.
On propose un schema reactionnel en accord avec les faits observes dans la reaction de disproportion des olefines acycliques, la polymerisation des olefines cycliques et la telomerisation des olefines cycliques par les olefines acycliques.
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