ROMP with Restraint
Science · 2005
Ring-opening metathesis polymerization (ROMP) yields a versatile range of linear polymers from cyclic olefin starting materials. The reaction is driven by relief of the bonding strain inherent to the geometry, as a metal catalyst pries open the monomer rings and stitches them together one by one. Whereas molybdenum and tungsten catalysts are more active, ruthenium compounds can react selectively with a C=C bond in the presence of many other groups, such as ketones and esters. The tradeoff for such a tolerant catalyst is reduced reactivity toward low-strain rings, such as cyclopentene and cycloheptene, which are appealing substrates because they can be functionalized symmetrically to yield regioregular polymers.