Cycloalkenes ring-opening metathesis polymerization

It has been shown that [(r]6-arene)RuCl2]2 6 and [(r 6-arene)RuCl2] PR3 7 complexes can be activated in situ to afford active metathesis catalysts, either on treatment with diazoalkanes [15] or by UV irradiation [16]. The structure of the active species thus formed is unknown, but it initiates the ring opening metathesis polymerization reactions (ROMP) of various cycloalkenes very efficiently. Therefore these in situ recipes may also be useful in the context of preparative organic chemistry. 

The polymerization of the alkyne triple bond (Secs. 5-7d and 8-6c) and ring-opening metathesis polymerization of a cycloalkene (Secs. 7-8 and 8-6a) yield polymers containing double bonds in the polymer chain. Cis-trans isomerism is possible analogous to the 1,4-polymer-ization of 1,3-dienes. 

Whereas only limited stereoselectivity is characteristic of the metathesis of acyclic olefins, ring-opening metathesis polymerization of cycloalkenes may be highly stereoselective provided the proper catalysts and reaction conditions are selected. Cyclopentene, for instance, is transformed to either all-cis [Eq. (12.25)] or all-frans polypentenamers [Eq. (12.26)] in the presence of tungsten catalysts 21 92... 

VIII. RING-OPENING METATHESIS POLYMERIZATION (ROMP) OF CYCLOALKENES... 

Remarkable development over the last 10-15 years in the synthesis of well-defined functional-group-tolerant ruthenium carbenes (Grubbs-related catalysts) also caused real development of the metathesis-based reactions in organosilicon polymers. For recent reviews on metathesis of organosilicon compounds see Refs. [6,7]. Unsaturated organosilicon polymers can be synthesized via ruthenium carbene catalyzed ring-opening metathesis polymerization (ROMP) of silylsubstituted cycloalkenes (Eq. 113). 

When certain cycloalkanes are used in metathesis reactions, ring-opening metathesis polymerization (ROMP) occurs to form a high molecular weight polymer, as shown with cyclopentene as the starting material. The reaction is driven to completion by relief of strain in the cycloalkene. 

Up to now, all processes developed industrially for the production of polymers by olefin metathesis involve ring opening metathesis polymerization of cycloalkenes. 

Figure 8. Ring opening metathesis polymerization (ROMP) of cycloalkenes with perfluoroalkyl substituted internal alkene...

Al-Samak, B. Amir-Ebrahimi, V. Corry, D. G Hamilton, J. G Rigby, S. Rooney, J. J. Thompson, J. M. Dramatic solvent effects on ring-opening metathesis polymerization of cycloalkenes. J. Mol. Catal. A Chem. 2000,160,13-21. 

Z/E Isomerism (generally indicated by cis/trans). This is found in polymers obtained from conjugated dienes or by ring-opening metathesis polymerization of cycloalkenes (polyalkenamers). The example illustrated hereafter is that of 1,4-polyisoprene (or 2-methylbuta-l,3-diene). It is important from an economical point of view—in particular, in the industry of natural and synthetic elastomers. 

Crotonaldehyde, hydrogenation of, 43-48 Cubane, isomerization of, 148 Cyclic dienes, metathesis of, 135 Cyclic polyenes, metathesis of, 135 Cycloalkenes, metathesis of, 134-136 kinetic model, 164 ring-opening polymerization, 143 stereoselectivity, 158-160 transalkylation, 142-144 transalkylidenation, 142-144 Cyclobutane configuration, 147 geometry of, 145, 146 Cyclobutene, metathesis of, 135 1,5,9-Cyclododecatriene, metathesis of, 135... 

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