Stereoselective Cyclopolymerization of 1,6-Heptadienes

Significance

Osakada and co-workers reported a stereoselective cyclopolymerization of 1,6-heptadiene (3) to poly-3 catalyzed by Fe and Co catalysts with bis(imino)pyridine ligands (1a-2b) in presence of the modified methylaluminoxane (MMAO). These complexes were reported to catalyze cyclopolymerization of both substituted and unsubstituted 1,6-heptadienes. It is remarkable that these polymerizations are also stereoselective. Cyclopolymerization of unsubstituted 1,6-dienes by Pd complexes is plagued by the formation of π-allylic palladium species, while that of complexes of early transition metals such as Ti, Zr, and Y lack stereoselectivity. The authors also noted that the cyclopolymerizations by Fe and Co complexes (1a-2b) lead to complete polymerization, whereas those of early transition metals (Ti, Zr, and Y) often leave partial structures harboring vinyl groups.