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Unformatted text preview: The Olefin Metathesis Reaction Chem 215 Myers Reviews: Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew. Chem., Int. Ed. Engl. 2005 , 44 , 4490–4527. Grubbs, R. H. Tetrahedron 2004 , 60 , 7117–7140. Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem. Soc. 2003 , 125 , 11360–11370. Connon, S. J.; Blechert, S. Angew. Chem., Int. Ed. Engl. 2003 , 42 , 1900–1923. Fürstner, A. Angew. Chem., Int. Ed. Engl. 2000 , 39 , 3013–3043. Grubbs, R. H.; Chang, S. Tetrahedron 1998 , 54 , 4413–4450. Armstrong, S. K. J. Chem. Soc., Perkin Trans. 1 1998 , 371–388. n ROMP Ring-Opening Metathesis Polymerization (ROMP): • ROMP is thermodynamically favored for strained ring systems, such as 3-, 4-, 8- and larger-membered compounds. • When bridging groups are present (bicyclic olefins) the Δ G of polymerization is typically more negative as a result of increased strain energy in the monomer. • Block copolymers can be made by sequential addition of different monomers (a consequence of the "living" nature of the polymerization). H 2 C CH 2 RCM Ring-Closing Metathesis (RCM): • The reaction can be driven to the right by the loss of ethylene. • The development of well-defined metathesis catalysts that are tolerant of many functional groups yet reactive toward a diverse array of olefinic substrates has led to the rapid acceptance of the RCM reaction as a powerful method for forming carbon-carbon double bonds and for macrocyclizations. • Where the thermodynamics of the closure reaction are unfavorable, polymerization of the substrate can occur. This partitioning is sensitive to substrate, catalyst, and reaction conditions. + R 1 R 2 R 3 R 4 R 1 R 3 R 2 R 4 Cross Metathesis (CM): + + CM • Self-dimerization reactions of the more valuable alkene may be minimized by the use of an excess of the more readily available alkene. 3-Ru (Grubbs' 1st Generation Catalyst) N Mo O O i- Pr i- Pr CH 3 CH 3 Ph H F 3 C CH 3 F 3 C F 3 C CH 3 F 3 C 1-Mo P( c-Hex) 3 Ru P( c-Hex) 3 H Cl Cl 2-Ru P( c-Hex) 3 Ru P( c-Hex) 3 H Cl Ph Cl Catalysts • The well-defined catalysts shown above have been used widely for the olefin metathesis reaction. Titanium- and tungsten-based catalysts have also been developed but are less used. • Schrock's alkoxy imidomolybdenum complex 1-Mo is highly reactive toward a broad range of substrates; however, this Mo-based catalyst has moderate to poor functional group tolerance, high sensitivity to air, moisture or even to trace impurities present in solvents, and exhibits thermal instability. • Grubbs' Ru-based catalysts exhibit high reactivity in a variety of ROMP, RCM, and CM processes and show remarkable tolerance toward many different organic functional groups....
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This note was uploaded on 04/07/2008 for the course CHEM 215 taught by Professor Shair during the Fall '07 term at Harvard.
- Fall '07