Models for Intermediates in Metallocene-Catalyzed Alkene Polymerization: Alkene Dissociation from Cp2Zr[η1,η2-CH2Si(CH3)2CH2CHCH2][B(C6F5)4]

The bis(allyldimethylsilylmethyl)bis(cyclopentadienyl)zirconium complex Cp 2 Zr[CH 2 Si(CH 3 ) 2 CH 2 CH CH 2 ] 2 ( 5 ) reacted rapidly with [(C 6 H 5 ) 2 (CH 3 )NH][B(C 6 F 5 ) 4 ] in CD 2 Cl 2 at −78 °C to form the cationic zirconium−alkyl−alkene complex Cp 2 Zr[η 1,η 2 -CH 2 Si(CH 3 ) 2 CH 2 CH CH 2 ][B(C 6 F 5 ) 4 ] ( 6 ). Low-temperature 1 H and 13 C NMR spectroscopy established the coordination of the tethered alkene to the d 0 metal center. Line shape analysis of the coalescence of the diastereotopic Cp ligand resonances allowed measurement of the alkene dissociation energy barrier [Δ G ⧧ (−28 °C) = 12.7 ± 0.8 kcal mol - 1 ].