Scandium-Catalyzed Regio- and Stereoselective Cyclopolymerization of Functionalized α,ω-Dienes and Copolymerization with Ethylene

The precise control of regio- and stereochemistry in the cyclopolymerization of heteroatom-functionalized α,ω-dienes is of much interest and importance, but has remained a challenge to date. We report herein the regio-, diastereoselective and stereoregular cyclopolymerization of ether- and thioether-functionalized 1,6-heptadienes by a half-sandwich scandium catalyst. The polymerization of 4-benzyloxy-1,6-heptadiene selectively afforded the corresponding benzyloxy-functionalized cyclic polymer composed of 1,2,4-cis-substituted-ethylenecyclopentane (ECP) microstructures in a isospecific fashion (95% mmm). In contrast, the polymerization of 4-phenylthio-1,6-heptadiene exclusively yielded 1,2-trans-1,4-cis-ECP units with high isotacticity (95% rrr). The DFT calculations revealed that an interaction between the scandium atom in the catalyst and the heteroatom in a diene monomer played an important role in controlling the regio- and stereochemistry of the diene cyclopolymerization. The copolymerization of functionalized 1,6-heptadienes with ethylene has also been achieved in a controlled fashion.