Recent Advances in the Regio- and Stereospecific Cyclopolymerization of α,ω-Diynes by Tailored Ruthenium Alkylidenes and Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes

Recent accomplishments in the cyclopolymerization of α,ω-diynes by tailored Ru- and Mo-alkylidenes are reported. Special emphasis is put on the extent and origin of both stereo- and regioselectivity with the different initiator systems used. Particularly, the very recently developed molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes are of utmost interest since they allow for the cyclopolymerization of α,ω-diynes bearing protic functional groups such as hydroxyls and carboxylic acids and therefore rival Ru-alkylidenes both in terms of regio- and stereoselectivity but also in terms of activity and functional group tolerance.