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Journal ArticleDOI

W(CO)6/CBr4/hv — a new system for metathesis polymerisation

14 Jan 1997-Journal of Molecular Catalysis A-chemical (Elsevier)-Vol. 115, Iss: 1, pp 79-84
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.

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Topics: Ring-opening metathesis polymerisation (61%), Norbornene (53%), Metathesis (52%) ...read more
Citations
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Journal ArticleDOI
Ragnar S. Stoll1, Stefan Hecht1Institutions (1)
12 Jul 2010-Angewandte Chemie
TL;DR: This Review outlines the general concept of light-gated catalysis based on photocaged and also photoswitchable systems, and discusses relevant examples of the past and recent literature.

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Abstract: Having control over an entity or even an entire process is arguably the ultimate demonstration of its understanding and it will enable its potential to be fully exploited. With this in mind, chemists have not only been creating and optimizing a myriad of different catalysts for most (relevant) chemical reactions over the past decades, but have recently started to implement controlling elements into the catalyst design. These incorporated gates operate upon exposure to suitable control stimuli, and light represents perhaps the scientifically and technologically most attractive stimulus. In principle, irradiation can thereby induce activity and selectivity in a given catalyst system with high spatial and temporal control, leading to an overall localization and amplification of an optical signal and translation into chemical action. While nature has developed and utilized this concept, in particular in the processes of vision and photomovement, such artificial photocontrolled catalyst systems offer unique opportunities and have high potential for future applications. In this Review, we outline the general concept of light-gated catalysis based on photocaged and also photoswitchable systems, and discuss relevant examples of the past and recent literature.

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265 citations


Journal ArticleDOI
Dongren Wang1, Klaus Wurst2, Wolfgang Knolle1, Ulrich Decker1  +4 moreInstitutions (3)
14 Apr 2008-Angewandte Chemie
TL;DR: The development of the first thermally stable, truly UV-triggerable precatalysts for ROMP and their application in surface functionalization is reported.

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Abstract: Metathesis chemistry and, in the context of polymer chemistry, ring-opening metathesis polymerization (ROMP) have gained a strong position in chemistry and materials science. ROMP is strongly associated with two classes of well-defined metal alkylidene based initiators, molybdenumbased Schrock and ruthenium-based Grubbs type initiators. Despite the tremendous achievements in catalyst development, both families of initiators are still experiencing ongoing, vivid development. Most Grubbs type initiators work at room temperature or require only gentle warming to work properly. More recently, an increasing number of reports on latent Ru-based initiators has appeared. Such precatalysts are of particular interest in technical applications of ROMP, since they allow for premixing, that is, the preformulation of a monomer/precatalyst mixture, its storage over a longer period of time even at elevated temperatures (usually less than 45 8C), and, most importantly, the shaping and profiling of such mixtures prior to polymerization (“curing”). Numerous latent Grubbs type initiators have been reported recently; however, all these precatalysts are triggered thermally. By contrast, surface modification and functionalization require UV-triggerable precatalysts. Few such systems have been reported to date. The synthesis of photoactive Schrock type tungsten-based compounds as well as ruthenium and osmium arene compounds of the general formula [Ru(p-cymene)Cl2(PR3)] and [Os(p-cymene)Cl2(PR3)] (R= cyclohexyl, etc.) were first reported by van der Schaaf et al. They also investigated the photoinduced polymerization of different functionalized norbornenes and 7-oxanorbornenes using various [Ru(solvent)n]X2 complexes, (X= tosylate, trifluoromethanesulfonate) as well as Ru half-sandwich and sandwich complexes. Noels and co-workers reported on the visiblelight-induced ROMP of cyclooctene using [RuCl2(IMes)(pcymene)] (IMes= 1,3-dimesitylimidazol-2-ylidene). Some of these systems were also used in ring-closing metathesis reactions. Most of the systems available to date, however, have significant disadvantages. They either show low activity, resulting in low polymer yields (less than 30%) in the photochemically triggered process, or the irradiation wavelength necessary to trigger ROMP is 360 nm or higher. In the latter case, the initiatorsA thermal stability is generally poor, thus discouraging their application in photoinduced ROMP. Thus, none of the systems reported to date was entirely thermally stable above or even at room temperature. Therefore, these systems do not fulfill the requirements of a truly latent photocatalyst. Herein, we report the development of the first thermally stable, truly UV-triggerable precatalysts for ROMP and their application in surface functionalization. We commenced our investigations with [Ru(IMesH2)(CF3CO2)(tBuCN)4)] CF3CO2 (PI-1) and [Ru(IMes)(CF3CO2)(tBuCN)4)] CF3CO2 (PI-2), which were prepared from [Ru(CF3CO2)2(L)(p-cymene)] [31,32] (L= IMes or IMesH2, 1,3-dimesityl-4,5-diyhdroimidazolin-2-ylidene) by reaction with excess tBuCN. Both compounds can be handled in air. H and C NMR spectroscopy data and elemental analysis reveal the presence of one N-heterocyclic carbene (NHC) ligand, two inequivalent trifluoroacetate groups, and four tBuCN ligands, suggesting cationic Ru complexes. The structures of PI-1 and PI-2 were confirmed by X-ray analysis; the structure of PI-1 is shown in Figure 1 (see also the Supporting Information). Upon mixing of either PI-1 or PI-2 with monomers 3–8 (Scheme 1), no reaction was observed at room temperature within 24 h. Even highly reactive (distilled) dicyclopentadiene (4) did not react with PI-1 or PI-2 at room or elevated temperature (RT

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87 citations


Journal ArticleDOI
Ragnar S. Stoll1, Stefan Hecht1Institutions (1)
12 Jul 2010-Angewandte Chemie
Abstract: Kontrolle uber einen Gegenstand oder einen gesamten Prozess auszuuben, ist zweifelsohne der ultimative Beweis fur dessen Verstandnis und ermoglicht erst die vollstandige Nutzung seines Potenzials. Vor diesem Hintergrund haben Chemiker in den vergangenen Jahrzehnten fur die meisten (relevanten) chemischen Reaktionen nicht nur eine Vielzahl von Katalysatoren entwickelt und optimiert, sondern vor kurzem auch damit begonnen, Steuerungselemente in das Katalysatordesign einzufuhren. Diese integrierten Kontrolleinheiten werden durch Einwirkung geeigneter Stimuli reguliert, wobei Licht aus wissenschaftlicher und technologischer Sicht vermutlich am attraktivsten ist. Bestrahlung kann hierbei prinzipiell sowohl Aktivitat als auch Selektivitat in einem gegebenen katalytischen System mit hoher raumlicher und zeitlicher Prazision steuern, die zu einer allgemeinen Lokalisierung und Verstarkung des optischen Signals und dessen Umwandlung in chemische Aktivitat fuhrt. Wahrend in der Natur dieses Konzept bereits erfolgreich Anwendung findet, im Speziellen beim Sehprozess und bei der Photobewegung, eroffnen derartige kunstliche lichtgesteuerte katalytische Systeme einzigartige Moglichkeiten und verfugen uber ein hohes Potenzial fur zukunftige Anwendungen. In diesem Aufsatz beschreiben wir die grundsatzliche Idee der lichtgesteuerten Katalyse basierend auf photoaktivierbaren und photoschaltbaren Systemen und diskutieren relevante Beispiele aus der alteren und neueren Literatur.

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81 citations


Journal ArticleDOI
Abstract: Current research in alkene metathesis has two significant strands of development. One pertains to rapid progress in catalyst development which permits far greater tolerance of organic functional groups. This includes synthesis of new, structurally defined, catalytically active molecules, some of them even performing in aqueous environment. The second aspect is a consequence of the first one. Not only polyfunctional polymeric materials are obtainable as a result of “living” ring-opening metathetic polymerisation of structurally complex monomers, but alkene metathesis provided an efficient ring-closing strategy for use in synthesizing intricate structural patterns of important organic molecules. In this review, the information is classified in terms of type of catalysis — homogeneous or heterogeneous. Each type is subdivided according to the metal used, so that a reactivity pattern might emerge to guide future developments.

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74 citations


Journal ArticleDOI
Yuval Vidavsky1, N. Gabriel Lemcoff1Institutions (1)
TL;DR: This survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.

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Abstract: Light activation is a most desirable property for catalysis control. Among the many catalytic processes that may be activated by light, olefin metathesis stands out as both academically motivating and practically useful. Starting from early tungsten heterogeneous photoinitiated metathesis, up to modern ruthenium methods based on complex photoisomerisation or indirect photoactivation, this survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.

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67 citations


References
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Journal ArticleDOI
01 Jul 1989-Macromolecules
Abstract: Synthese de polynorbornene et poly(exodicyclopentadiene) avec un groupe terminal aldehyde par polymerisation puis reaction avec le terephtalaldehyde. Ce groupe terminal sert a amorcer la polycondensation du t-butyldimethylsilyl vinylether conduisant a un copolymere sequence

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61 citations


Journal ArticleDOI
Wilhelm Risse1, Robert H. Grubbs1Institutions (1)
Abstract: The present paper reviews recent developments on the application of titanacyclobutaneinitiated ‘living’ olefin metathesis polymerization for the preparation of new polymer structures. These are block and graft copolymers containing polymer blocks obtained by olefln metathesis polymerization. The Wittig-type reaction of titanacyclobutane end groups allowed the preparation of AB-type diblock copolymers by changing from olefin metathesis to group transfer polymerization. The same type of reaction was used to link preformed polymer blocks to give ABA-type triblock copolymers and graft copolymers.

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35 citations


Journal ArticleDOI
Francis Garnier1, P. Krausz1, Henri Rudler2Institutions (2)
Abstract: Photochemically induced metathesis of RCHCHR′ olefins with W(CO) 6 and CCl 4 gives RCHCCl 2 and R′CHCCl 2 . W(CO) 6 in CCl 4 reacts under illumination with cyclic enol ethers to give products resulting from the insertion of metalladichlorocarbene moieties into the carbon—carbon double bond. A mechanism for the formation of these compounds is outlined.

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34 citations


Journal ArticleDOI
Abstract: In the photocatalytic system containing tungsten compounds of the type W(CO)5L (L = CO, py, PPh3, Cl−) and Group IIIb and IVab element halides (AXn), the metathesis of internal and terminal olefins was investigated. The terminal olefin metathesis reaction is accompanied by double bond migration yielding the internal olefins, which undergo co-metathesis with the initial olefins. Substitution of tungsten by molybdenum or chromium favours the isomerization reaction.

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27 citations


Journal ArticleDOI
H. Rudler1Institutions (1)
Abstract: Reaction of heteroatom or non-heteroatom stabilized alkylidene complexes of tungsten with cyclic enol ethers allowed us to observe products that arise from the insertion of the metal into the carbon—carbon double bond of the unsaturated starting compound. This reaction is compared with the ring opening polymerization of cyclic olefins. The reaction of a metathesis catalyst prepared from W(CO) 6 /CCl 4 /hν with such cyclic enol ethers gives products arising from the probable insertion of a dichlorocarbene complex of tungsten into the carbon—carbon double bond. Attempts to prepare dialkyl substituted alkylidene complexes of tungsten, starting from Fischer-type carbenes, and to trap them with cyclic enol ethers failed; instead, a new kind of stabilization of these complexes by the formation of dinuclear μ-alkylidene complexes was observed. The chemistry of these new complexes, as well as the possibility of their occurence in the olefin metathesis reaction, is outlined.

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22 citations