Observation of zirconium allyl species formed during zirconocene-catalyzed propene polymerization and mechanistic insights

Oligomeric Cp 2 Zr + –allyl species were detected in reaction mixtures of either [Cp 2 ZrMe][MeB(C 6 F 5 ) 3 ] or [Cp 2 ZrMe][B(C 6 F 5 ) 4 ] with propylene by a combination of 1 H NMR spectroscopy and electrospray ionization (tandem) mass spectrometry techniques. Conjointly, the data imply that formation of Cp 2 Zr + –allyl species occurs via (re)coordination of alkene (propylene and vinylidene end groups of unsaturated polymer chains, respectively) to Cp 2 Zr + R (R = CH 3 , H, polymeryl), followed by intramolecular proton transfer from Cγ to R and release of RH. Analysis of the olefinic region of the 1 H NMR spectra of the reaction mixture obtained from [Cp 2 ZrMe][MeB(C 6 F 5 ) 3 ] and propylene reveals the presence of a triplet resonance at δ  ∼ 5.2, which was attributed to the unprecedented 3-propenyl end group. A plausible mechanism for the origin of the 3-propenyl end groups is discussed. Additionally, a mechanism for incorporation of stereodefects into stereoregular polymers is also discussed. The cationic Cp 2 Zr + –allyl intermediates formed during polymerization may contribute to catalyst deactivation.