Olefin metathesis acyclic diene

Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

As stated above, olefin metathesis is in principle reversible, because all steps of the catalytic cycle are reversible. In preparatively useful transformations, the equilibrium is shifted to one side. This is most commonly achieved by removal of a volatile alkene, mostly ethene, from the reaction mixture. An obvious and well-established way to classify olefin metathesis reactions is depicted in Scheme 2. Depending on the structure of the olefin, metathesis may occur either inter- or intramolecularly. Intermolecular metathesis of two alkenes is called cross metathesis (CM) (if the two alkenes are identical, as in the case of the Phillips triolefin process, the term self metathesis is sometimes used). The intermolecular metathesis of an a,co-diene leads to polymeric structures and ethene this mode of metathesis is called acyclic diene metathesis (ADMET). Intramolecular metathesis of these substrates gives cycloalkenes and ethene (ring-closing metathesis, RCM) the reverse reaction is the cleavage of a cyclo-... 

Scheme 2 Different modes of the olefin metathesis reaction cross metathesis (CM), ringclosing metathesis (RCM), ring-opening metathesis (ROM), acyclic diene metathesis polymerization (ADMET), and ring-opening metathesis polymerization (ROMP)...

Olefin metathesis, an expression coined by Calderon in 1967,1 has been accurately described in Ivin and Mol s seminal text Olefin Metathesis and Metathesis Polymerization as the (apparent) interchange of carbon atoms between a pair of double bonds (ref. 2, p. 1). This remarkable conversion can be divided into three types of reactions, as illustrated in Fig. 8.1. These reactions have been used extensively in the synthesis of a broad range of both macromolecules and small molecules3 this chapter focuses on acyclic diene metathesis (ADMET) polymerization as a versatile route for the production of a wide range of functionalized polymers. 

Scheme 10. Olefin metathesis RCM (ring closing metathesis), ROMP (ring opening metahesis polymerization), ADMET (acyclic diene metathesis), CM (cross metathesis).

Let us emphasise that the driving force for acyclic diene metathesis, which is a step-growth condensation polymerisation, is the release and removal of a small condensate molecule. The polycondensation is performed preferably under bulk conditions (no solvent used), since acyclic diene metathesis is thermally neutral and there is no need to remove the heat of the reaction, in contrast to exothermic cyclic olefin ring-opening metathesis polymerisation. 

In the ring-closing metathesis reaction, intramolecular metathesis closes a ring to form a small cyclic molecule with concurrent loss of a small molecule (ethylene). Conversely, in the case of the acyclic diene metathesis reaction, macromolecules are formed by successive intermolecular condensation of two olefinic molecules [1],... 

Also, a series of well-defined polyolefins, including perfectly branched polyethylene and ethylene/a-olefin copolymers, have been synthesised via acyclic diene metathesis polycondensation [scheme (28)] [47] these well-defined polyolefins have been designed to model the crystallisation of polyethylene and olefin copolymers. 

Thanks to the development of the Grubbs benzylidene catalyst (2) and other related ruthenium complexes, olefin metathesis has experienced spectacular advances over the past 10 years. The various incarnations of the reaction (acyclic diene metathesis, ring-closing metathesis, ring-opening metathesis polymerization, etc.) have now acquired first rank importance in synthesis. Clearly, the emergence of a similar, generic, efficient catalytic system for con-... 

Ring-closing metathesis methodology has been used to access 7-membered ring sultones (e.g. 278, n = 1, m = 1) efficiently from the acyclic diene precursor 277, which could readily be made in turn fom the appropriate olefinic sulfonyl chloride and alcohol [02SL2019]. 

Attention paid to olefin metathesis in organic synthesis has increased over recent years because of the progress in ring-closing metathesis [3]. This metathesis variation consists of the cycliza-tion of an acyclic (a, cu)-diene 5 and formation of... 

Title Synthesis of A,B-Alternating Copolymers by Olefin Metathesis Reactions of Cyclic Olefins or Olefinic Polymers with an Acyclic Diene... 

Olefin metathesis is a unique carbon skeleton redistribution in which unsaturated carbon-carbon bonds are rearranged in the presence of metal carbene complexes. With the advent of efficient catalysts, this reaction has emerged as a powerful tool for the formation of C-C bonds in chemistry [1]. Olefin metathesis can be utilized in five types of reactions ring-closing metathesis (RCM), ring-opening metathesis (ROM), respective ringopening metathesis polymerization (ROMP), cross-metathesis (CM), and acyclic diene metathesis polymerization (ADMET). 

To date there are only a few examples of polymers having a disilandiyl-carbon backbone, but they could not be synthesized by an olefin-metathesis process with Grubbs catalyst [4 - 6]. The aim of our work is to investigate the catalytic activity of the ruthenium-carbene complex RuCl2(PCy3)2(=CHPh) (Grubbs catalyst) in acyclic diene metathesis reactions of different unsaturated organodisilanes. 

Acyclic diene metathesis (ADMET) polymerization is an equilibrium step condensation during which the production and removal of C2H4 (when using terminal olefins) drive the reaction progress [18]. 

The next approach for obtaining higher molecular weight polymers was to explore acyclic diene metathesis (ADMET) polymerizations.The aim was to achieve higher molecular weight flame-resistant polymers. We modeled the reaction using aliphatic diene monomers such as 1,5-hexadiene and 1,9-deca-diene under test conditions to optimize conditions before making BPC-derived products. At this point, we decided to functionalize the BPC with an olefin. 

Wagener, K.B. Lehman, S.E. Comparison of the kinetics of acyclic diene metathesis promoted by Grubbs ruthenium olefin metathesis catalysts. Macromolecules 2002, 35, 48-53. 

Olefin metathesis (OM) has proven to be one of the most important advances in catalysis in recent years based on the application of this chemistry to the synthesis of polymers and biologically relevant molecules [1-10]. This unique transformation promotes chain and condensation polymerizations, namely ring opening metathesis polymerization and acyclic diene metathesis polymerization (ADMET). Applications of metathesis polymerization span many aspects of materials synthesis from cell-adhesion materials [11] to the synthesis of linear polyethylene with precisely spaced branches [12]. 

Scheme 1 Types of olefin metathesis reactions. ADMET=acyclic diene metathesis...

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