1.6- Heptadiyne cyclopolymerization

While classical catalysts usually result in ill-controlled polymerization systems, well-defined Schrock initiators cyclopolymerize 1,6-heptadiynes in a living manner - in most cases a class VI living manner (according to Matyjaszewski [84]). Polymers based on one single repetitive unit (poly(cyclopent-l-enylene-... 

A number of Mo carbene catalysts, bearing various modified ligands, have been reported and proven to elegantly induce living polymerization of acetylene monomers. The first example is the cyclopolymerization of 1,6-heptadiynes catalyzed by Mo carbenes Mo carbenes ligated by bulky imido and alkoxy groups are quite effective. In... 

Although the polymerization of diene monomers is most familiar for 1,3-dienes, as in the production of rubbers, the polymerization of 1,6-dienes to yield polymers containing six-membered rings ( cyclopolymerization ) has been well established for many years43. Gibson et al.441 have used cyclopolymerization of 1,6-diynes to prepare polymers which are effectively substituted polyacetylenes, the archetype being the polymerization of 1,6-heptadiyne ... 

Abstract Metathesis-based polymerizations of 1-alkynes and cyclopolymerizations of 1,6-heptadiynes using late transition metal catalysts are reviewed. Results obtained with both binary, ternary, and quaternary catalytic systems and well-defined molybdenum- and ruthenium-based catalysts are presented. Special consideration is given to advancements in catalyst design and mechanistic understanding that have been made in this area over the last few years advancements that have facilitated tailor-made syntheses of poly(ene)s. In addition, the first supported ruthenium-based cyclopolymerization-active systems are summarized. Finally, selected structure-dependent properties will be outlined where applicable. 

The cyclopolymerization of 1,6-heptadiynes represents a powerful alternative to 1-alkyne polymerization [81, 94]. Cyclopolymerizations may be accom-... 

In terms of polymer structure, cyclopolymerizations of 1,6-heptadiynes usually yield poly(ene)s that contain a mixture of five- and six-membered rings (Fig. 6). 

Fig. 6 Possible ring structures of poly( 1,6-heptadiynes) prepared via cyclopolymerization. Poly(cyclopent-l-enylene-l-vinylene)s (A) poly(cyclohex-l-ene-3-methylidene)s (B) and mixed structures (C)...

In order to understand the polymer structures that are obtained in the polymerization of 1,6-heptadiynes, one needs to consider all possible polymerization mechanisms. If 1,6-hep tadiynes are subject to cyclopolymerization using well-defined Schrock catalysts, polymerization can proceed via two mechanisms. One is based on monomer insertion, where the first alkyne group adds to the molybdenum alkylidene forming a disubstituted alkylidene, which then reacts with the second terminal alkyne group to form poly(ene)s consisting of five-membered rings. Analogous to 1-alkyne polymerization, one refers to this type of insertion as a-insertion (Scheme 4). 

Scheme 4 Two possible reaction pathways and resulting ring structures in the cyclopolymerization of 1,6-heptadiynes...

Scheme 6 Proposed mechanism of cyclopolymerization of 1,6-heptadiynes using a Ru-based initiator...

Regioselective Polymerization of 1-Alkynes and Stereoselective Cyclopolymerization of a,co-Heptadiynes... 

Cyclopolymerization of 1,6-heptadiyne having bulky substituents was effectively carried out by the MoCls-based catalysts, and their optimized polymerization results are summarized in Table 6. ° In most cases, the polymer yields were quantitative. And the result-... 

Molybdenum imido alkylidene complexes also have been employed for a variety of other catalytic reactions of interest to the organic or polymer chemist, among them selective cross-couplings of olefins, [99] polymerization of terminal alkynes, [100-102] step-growth polymerization of dienes, [103,104] and cyclopolymerization of 1,6-heptadiynes. [105-107]... 

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