End-Group-Confined Chain Walking within a Group 4 Living Polyolefin and Well-Defined Cationic Zirconium Alkyl Complexes for Modeling This Behavior

摘要

One of the last remaining mysteries associated with the Ziegler-Natta polymerization of propene by zirconocene-based catalysts is the mechanism by which chain-end epimerization of the last generated stereocenter occurs under conditions of low monomer concentration. In this regard, Landis and co-workers1f recently reported the direct observation of chain-end epimerization of living zirconocene polypropylene by low-temperature NMR spectroscopy. Simple model complexes for this process are still required, however, as they should greatly facilitate mechanistic studies.