Enantioselective epoxide polymerization using a bimetallic cobalt catalyst.

A highly active enantiopure bimetallic cobalt complex was explored for the enantioselective polymerization of a variety of monosubstituted epoxides. The polymerizations were optimized for high rates and stereoselectivity, with s-factors (k(fast)/k(slow)) for most epoxides exceeding 50 and some exceeding 300, well above the threshold for preparative utility of enantiopure epoxides and isotactic polyethers. Values for mm triads of the resulting polymers are typically greater than 95%, with some even surpassing 98%. In addition, the use of a racemic catalyst allowed the preparation of isotactic polyethers in quantitative yields. The thermal properties of these isotactic polyethers are presented, with many polymers exhibiting high T(m) values. This is the first report of the rapid synthesis of a broad range of highly isotactic polyethers via the enantioselective polymerization of racemic epoxides.

Isospecific polymerization of racemic epoxides: a catalyst system for the synthesis of highly isotactic polyethers.

A highly active bimetallic cobalt catalyst system is reported for the polymerization of racemic terminal epoxides to yield isotactic polyethers.

Enantioselective polymerization of epoxides: a highly active and selective catalyst for the preparation of stereoregular polyethers and enantiopure epoxides.

A chiral, bimetallic cobalt catalyst was discovered that is highly active and enantioselective for epoxide polymerization. The enantiomerically pure catalyst system exhibits a stereoselectivity factor (s = k(fast)/k(slow)) of 370 for propylene oxide, allowing enantiomerically pure epoxide to be recovered in nearly the maximum theoretical yield. In addition, the racemic catalyst forms highly isotactic poly(propylene oxide) in quantitative yield. The catalyst is active and selective for other epoxides, such as 1-butene oxide, 1-hexene oxide, and styrene oxide.