Ring-opening metathesis stereochemistry

Polymers formed by the ring-opening metathesis polymerisation (ROMP) reaction [54] exhibit a wide variety of microstructures which may be evaluated by specctroscopic techniques. The first ROMP polymers were analysed by IR spectroscopy [55], but that can only determine the absolute stereochemistry of... 

The ring-opening polymerization of a simple cyclic olefin such as cyclooctene yields two structures of maximum order, which are distinguished by the configuration (cis or irans) of their main-chain olefins. In contrast, polymers made from bicyclic olefins such as norbornene are inherently more complicated and have four structures of maximum order (Scheme 24). In addition to cis- and trans-olefins, the polymers can also be isotactic or syndiotactic. The stereochemistry of these polymers becomes even more complicated when the monomer is asymmetric, since head—head, head—tail, and tail—tail regioisomers are possible. Nevertheless, single-site metathesis catalysts have been developed that can control polymer stereochemistry to an impressive degree by both chain-end and site-control mechanisms. ° ° ... 

Ho Huu Thoi Ivin, K. J. Rooney, J. J. Tacticity and stereochemistry in the ring-opening polymerization of 5,5-dimethylbicyclo[2.2.1]hept-2-ene initiated by metathesis catalysts. J. Mol. Catal. 1982, 15, 245-270. 

Calderon was the first to find a catalyst system that would initiate both ring-opening polymerization of olefins (subsequendy named ROMP by Tim Swager when he was a student at Caltech) and acydic metathesis of simple olefins. Up until his findings, most catalysts for acydic metathesis were heterogeneous systems, and metal salts were used to polymerize strained olefins such as norbomenes. Beautiful work was carried out using the poorly defined systems to work out the stereochemistry and mechanism of metathesis. This beautiful work provides an excellent backdrop for the work described here. This section will focus on the use of well-defined complexes as initiators for the living polymerization of cydic olefins. 

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