Isotactic-specific polymerization of propene with an iron-based catalyst: polymer end groups and regiochemistry of propagation

Prevailingly isotactic poly(propylene) samples were prepared with a homogen eous catalytic system based on a bis(imino)pyridyl Fe(II) derivative and me thylaluminoxane. The polymer microstructure is in agreement with Bernoullia n statistics of dyad formation, implicating a "chain-end" mechanism of ster ic control. The latter is operative even at polymerization temperatures as high as +50 degrees C. NMR analysis of polymer end groups indicates that ch ain growth proceeds via 2,1 monomer insertion. The last two findings are un precedented for isotactic-specific polymerization of propene and are reason ably related to each other.