Ring-expansion metathesis polymerization

A system obeying such an equilibration scheme has been proposed by Grubbs and coworkers.It is the ring-expansion metathesis polymerization of cyclic olefins catalysed by a cyclic mthenium complex. The synthesis of cyclic polyoctenamers using ris-cyclooctene as the monomer is illustrated in Scheme 5. 

Boydston AJ, Xia Y, Komfield JA, Gorodetskaya lA, Grubbs RH. Cycbc mtheruum-alkybdene catalysts for ring-expansion metathesis polymerization. J Am Chem Soc. 2008 130 12775-12782. 

Xia Y, Boydston AJ, Yao Y, et al. Ring-expansion metathesis polymerization catalyst-dependent polymerization profiles. J Am Chem Soc. 2009 131 2670-2677. 

Another most recent and successful example concerns the ring-expansion metathesis polymerization (REMP) of cycloolefins using cyclic carbene-ruthenium complex. " In this reaction, the cyclic olefin coordinates onto the ruthenium active center before insertion into the cyclic carbene ring. 

Cyclic bottlebrush polymers are uniquely accessible in high yields through ring-expansion metathesis polymerization (REMP) (Figure 8.14). For example, the alkyne-containing macrocycle 27 was modified with PEG substituents to generate cyclic bottlebrush copolymer 28, which exists as a toroid [141]. To date, REMP has yielded bottlebrushes that serve as proof of concept, and it will be interesting to see whether this toroidal shape makes a difference in their function. 

Boydston AJ, Holcombe TW, Unmh DA, Frechet JMJ, Gmbbs RH (2009) A direct route to cyclic organic nanostmctures via ring-expansion metathesis polymerization of a dendronized macromonomers. J Am Chem Soc 131 5388-5389... 

More recently, the same principle was applied by the same authors to cyclic alkanes for catalytic ring expansion, contraction and metathesis-polymerization (Scheme 13.24) [44]. By using the tandem dehydrogenation-olefin metathesis system shown in Scheme 13.23, it was possible to achieve a metathesis-cyclooligomerization of COA and cyclodecane (CDA). This afforded cycloalkanes with different carbon numbers, predominantly multiples of the substrate carbon number the major products were dimers, with successively smaller proportions of higher cyclo-oligomers and polymers. 

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