Kinetic and mechanistic aspects of metallocene polymerisation catalysts

For over 40 years metallocene complexes of titanium, zirconium and hafnium have been studied as catalysts in olefin polymerisations and are now of major industrial importance. This review summarises recent advances in mechanistic understanding of well defined metallocene catalysts based on ion pairs [L 2 ZrR + ⋯ X − ]. The interplay of ligand structure and nature of the counteranions demonstrates a fascinating subtlety that continually challenges our ability to rationalise and predict catalyst performance. The nature of the counteranion is an essential component of metallocene polymerisation catalysts. Detailed mechanistic investigations show how the anion is able to determine the activity and, in many cases, also the stereoselectivity of the catalyst. This review summarises recent advances in mechanistic understanding of well defined metallocene catalysts based on ion pairs [L 2 ZrR + ⋯X − ] and describes recent insights in ion mobility and kinetics of alkene polymerisation processes. The interplay of ligand structure and nature of the counteranions demonstrates a fascinating versatility and subtlety that continually challenge our ability to rationalise and predict catalyst performance.