POTENTIAL CATALYST DEACTIVATION REACTION IN HOMOGENEOUS ZIEGLER-NATTAPOLYMERIZATION OF OLEFINS - FORMATION OF AN ALLYL INTERMEDIATE

We investigate the possibility of premature deactivation of d(0) trans ition metal Ziegler-Natta metallocene catalysts Cp'2MR+ (Cp' = any cyc lopentadienyl derivative) used in homogeneous olefin polymerization. D ensity functional calculations show that beta-hydride elimination from the P-agostic precursor likely leads to formation of an allyl dihydro gen complex. This complex is prone to eject the dihydrogen ligand and form a ''torpid'' Cp'M-2 (allyl)(+) complex that can be slow to restar t chain propagation, depending on the steric hindrance imposed on the metal by the Cp' moiety. Our theoretical observations are in line with previous experimental evidence for such a reaction.