Catalysts Acyclic diene metathesis catalyst

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

K. Nomura, H. Morimoto, Y. Imanishi, Z. Ramhani, and Y. Geerts, Synthesis of high molecular weight rra i-poly(9,9-di- -octylfluorene-2,7-vinylene) by the acyclic diene metathesis polymerization using molybdenum catalysts, J. Polym. Sci., Part A Polym. Chem., 39 2463-2470, 2001. 

Acyclic diene metathesis (ADMET) polymerization of divinyl benzene, shown in Scheme 37, using an extremely reactive tungsten alkylidene catalyst (Schrock s catalyst) yielded PPV oligomers with DP of 8 [153]. In this example ethylene is formed as a side product of metathesis, and its removal by the use of high vacuum helps drive the polymerization in the forward direction. 

Cyclolinear carbosilane polymers with disilacyclobutane rings in the main-chain structure were prepared by means of acyclic diene metathesis (ADMET) polymerization of the corresponding l,3-dibutenyl-l,3-disilacyclobutanes in the presence of Grubbs catalyst (Scheme 13) <2003PP789, 2004MM5257, 2004PP118>. 

Lewis acid-free catalysts for acyclic diene metathesis obviate the formation of carbocations, which in turn completely eliminates competing reactions, mostly involving cationic oligomerisation via 1-alkene bonds. Thus, metathesis polycondensation occurs quantitatively to yield high molecular weight poly(l-alke-nylenejs with vinyl end groups and ethylene as a byproduct. 

The ruthenium-based catalyst provided by Grubbs et al. [19] also promotes acyclic diene metathesis polycondensation, although with higher concentrations being required to achieve reasonable reaction rates [24,25] ... 

Catalyst and monomer development in acyclic diene metathesis remains a subject of interest, the goal being to obtain macromolecules with well-defined backbone structures and architectures by easily accessible and less expensive means. By the application of an appropriate design of monomers and a careful choice of catalysts, a variety of non-functionalised and functionalised dienes have been polymerised via metathesis condensation to high molecular weight polymers. 

Indicate the main features differentiating acyclic diene metathesis polycondensation and single C-C bond-forming polycondensation with respect to the kind of monomers and catalyst action. 

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-... 

A new acyclic diene metathesis polymerization method has been developed using 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene)benzylidene mthenium(II) dichloride as catalyst. This reaction catalyst was used for preparing oligomers and polymers containing amino acids or polypeptides. 

In an earlier investigation by the author [1] an additional acyclic diene metathesis ruthenium polymerization catalyst, (I), was identified and used in the metathesis of alkenyl alcohols. 

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. 

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. 

The same acidic chloroaluminate ionic liquids have been used as solvent for tungsten aryl oxide complexes for the metathesis of alkenes [24]. Slightly acidic chloroaluminates also dissolve the [Cl2W=NPh(PMe3)3] complex which catalyze ethene oligomerization without the addition of co-catalysts [25]. In a similar way, Ni-catalyzed 1-butene dimerization into linear octenes was carried out in acidic chloroaluminates buffered with small amount of weak bases [26]. Neutral chloroaluminates (l-ethyl-3-methylimidazolium chloride/AlCl3 = 1) were employed to immobilize ruthenium carbene complexes for biphasic ADMET (acyclic diene metathesis) polymerization of an acyclic diene ester [27]. 

The most recent application of olefin metathesis to the synthesis of polyenes has been described by Tao and Wagener [105,117], They use a molybdenum alkylidene catalyst to carry out acyclic diene metathesis (ADMET) (Fig. 10-20) on either 2,4-hexadiene or 2,4,6-octatriene. The Wagener group had earlier demonstrated that, for a number of nonconjugated dienes [118-120], these polymerizations can be driven to high polymer by removal of the volatile product (e. g., 2-butene). To date, insolubility limits the extent of polymerization of unsaturated monomers to polyenes containing 10 to 20 double bonds. However, this route has some potential for the synthesis of new substituted polyacetylenes. Since most of the monomer unit is preformed before polymerization, it is possible that substitution patterns which cannot be incorporated into an alkyne or a cyclic olefin can be built into an ADMET monomer. 

Figure 10-20 The early stages of acyclic diene metathesis (ADMET). The reaction is driven by pumping off volatile products. When X is a double bond and R is methyl (i. e., 2,4,6-octatetraene), oligomeric polyenes are formed using a molybdenum alkylidene catalyst [105, 117],...

The chemist of metathesis polymerization has been applied to preparation of unsaturated polycarbonates. This is a case of an acyclic diene metathesis. It takes place when Lewis-acid free catalysts are employed. An example of one such catalyst is Mo[CHC(CH3)2Ph](A 2,6-C6H3-/-Pt2)[OCCH3(CF3)2]2. One interesting point about this process is that unconjugated dienes are polymerized to high molecular weight linear polymers without formation of any cyclic structures. 

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