ROMP ring opening alkene

SCHEME 1. Types of alkene and alkyne metathesis reactions. DBC, double bond cleavage TBC, triple bond cleavage ADMET, acyclic diene metathesis RCM ring-closing metathesis ROMP ring-opening metathesis polymerization... 

E2S.il (a) Ring opening alkene metathesis polymerization. ROMP can result in reduced steric strain, thereby providing a thermodynamic driving force for the reaction. 

Since one of the substrates is a cyclic alkene there is now the possibility of ring-opening metathesis polymerisation (ROMP) occurring which would result in the formation of polymeric products 34 (n >1). Since polymer synthesis is outside the scope of this review, only alkene cross-metathesis reactions resulting in the formation of monomeric cross-coupled products (for example 30) will be discussed here. 

One special case of cross metathesis is ring-opening cross metathesis. When strained, cyclic alkenes (but not cyclopropenes [818]) are treated with a catalytically active carbene complex in the presence of an alkene, no ROMP but only the formation of monomeric cross-metathesis product is observed [818,937], The reaction, which works best with terminal alkenes, must be interrupted when the strained cycloalkene is consumed, to avoid further equilibration. As illustrated by the examples in Table 3.22, high yields and regioselectivities can be achieved with this interesting methodology. 

Olefin metathesis (olefin disproportionation) is the reaction of two alkenes in which the redistribution of the olelinic bonds takes place with the aid of transition metal catalysts (Scheme 7.7). The reaction proceeds with an intermediate formation of a metallacyclobutene. This may either break down to provide two new olefins, or open up to generate a metal alkylidene species which -by multiple alkene insertion- may lead to formation of alkylidenes with a polymeric moiety [21]. Ring-opening metathesis polymerization (ROMP) is the reaction of cyclic olefins in which backbone-unsaturated polymers are obtained. The driving force of this process is obviously in the relief of the ring strain of the monomers. 

The ring-opening metathesis polymerization (ROMP) of cyclic alkenes yields polymers that still contain all double bonds [Eq. (13)]. 

Alkene metathesis, a remarkable reaction catalyzed by transition metal catalysts, can be traced back to Ziegler-Natta chemistry as its origin [11], In 1964, Natta et al. reported a new type polymerization of cyclopentene using Mo- or W-based catalyst, without knowing the mechanism. This was the first example of ring-opening metathesis polymerization (ROMP eq. 1.9) [12],... 

R and R refer to organic groups that contain some number of carbon atoms and may or may not be different from each other. With cyclic alkenes, metathesis leads to polymerization (specifically, ring-opening metathesis polymerization [ROMP]), shown here for cyclopentene ... 

Metathesis of alkenes is essentially a class of reactions where an interchange of C atoms between pairs of double bonds takes place. A few representative examples are shown by the reactions listed in Fig. 7.10. The industrial use of metathesis reactions so far has been limited mainly to exchange metathesis (Fig. 7.10, top, backward reaction) as in the SHOP process, and ring-open metathesis polymerization (ROMP). As already mentioned (Section 7.5), Vas-tenamer is a polymer made by Hulls by ROMP from cyclooctene. Similarly, the polymer from norborene by ROMP is manufactured by CdF Chemie and is sold by the trade name of Norsorex . 

Other methods developed by Grubbs136 for ruthenium complexes which can act as catalysts for ring opening metathesis polymerization (ROMP) and metathesis of conjugated and cumulated alkenes include the following ... 

Unsaturated polymers can be produced by means of ring-opening metathesis polymerization (ROMP) of cyclic alkenes. These unique polymers can also be produced via intermolecular Acyclic Diene Metathesis (ADMET). Dienes can also react intramolecularly via Ring Closing Metathesis (RCM) to afford cyclic products. RCM is often applied to synthesis of compounds for fine chemical and pharmaceutical application. Generic examples of these reactions are shown in Figure 2. 

Ring opening metathesis polymerization, which has been known since the discovery of the alkene metathesis reaction, has been given the acronym ROMP in recent years. In fact, the ROMP reaction was the first observation made in alkene metathesis chemistry, while the discovery of the exchange reaction in equation (1) actually occurred later. Acychc diene metathesis (ADMET) polymerization (equation 3) has only recently been shown to be a viable method for polymer synthesis, and it has been termed ADMET polymerization. ROMP reactions are driven by the release of ring strain from the monomer, while ADMET polymerization is driven by a shift in the equilibrium caused by the removal of one of the reaction products. 

W(NAr)(=CHBuO(OR)2 (R = CMe(CF3)2, 50) are highly active catalysts for the metathesis of internal alkenes (equation 16), and also effect the stereoselective olefmation of hydroxy ketones (equation 17). The reactivity of these catalysts can be tuned by varying the aUcoxide ligands for example, when R = Bn, the complex acts only upon strained cyclic alkenes and is a highly effective ring-opening metathesis polymerization (ROMP) catalyst (see Metathesis Polymerization Processes by Homogeneous Catalysis). 

Ri r3 In an alkene metathesis two alkenes react with an appropriate catalyst to form two new alkenes. There are different types of alkene pj2 r4 metathesis reactions The intermolecular reaction is called cross metathesis (CM), whereas intramolecular metathesis is divided into ring-closing metathesis (RCM) and ring-opening metathesis (ROM). Also two polymerization versions of alkene metathesis exist metathesis polymerization of acyclic dienes and ring-opening metathesis polymerization (ROMP). 

The ring-opening metathesis polymerization (ROMP, cf. Section 2.3.3) of strained-ring cyclic alkenes has attracted considerable attention in recent years due to the discovery that well-characterized metallacyclobutane [24] and metal alkylidene [25] complexes catalyze the living polymerization of monomers such as norbomene. Unfortunately, these catalysts often sulfer deactivating side reactions... 

In ring-opening methathesis polymerization (ROMP), a strained alkene such as norbomene is allowed to undergo metathesis with itself to give a polymer. 

The development of living ring-opening metathesis polymerization (ROMP cf. Section 6.10) catalysts was greatly influenced by the initial use of hydrated late transition metal salts. In the aqueous polymerization of 7-oxanorbornene derivatives, RuC13 and [Ru(H20)6]2+ were found to produce polymer with the latter having a smaller induction period [68], A key intermediate and product in the reaction is the alkene adduct, [Ru(H20)5(alkene)]2+ with the use of RuC13 and... 

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