Neopentyl zirconocene complex

Reversible (3-methyl elimination takes place on warming a solution of cationic (neopentyl)zirconocene complex 50 to 25°C, affording (methyl)zirconocene complex 51 and isobutene [69]. 

A more straightforward example of p-alkyl elimination is illustrated by the cationic neopentyl zirconocene and hafnocene complexes in Equation 10.20. - ° This p-alkyl elimination occurs in high yield to form the corresponding methyl complex and free isobutylene, even at -15 °C. A comparative study of the rates of reaction of the Zr and Hf complexes show that the two complexes react with similar rates and that the differences in the enthal-pic and entropic parameters offset each other. 

Direct (3-Mo elimination was observed when activating zirconocene methyl neopentyl complexes with B(C6F5)3.555 With sterically bulky Cp ligands, instantaneous isobutylene elimination is observed at — 75 °G however, for the bis-(Cp) compound, the zwitterionic neopentyl complex species is stable at 0 °C but undergoes clean and reversible f3-Me elimination at 25 °C (Scheme 177). This finding is consistent with (3-Me elimination as the major chain-transfer pathway in propylene polymerizations using a sterically encumbered metallocene catalyst. 

Hortonobserved direct /1-Me elimination in activating zirconocene methyl neopentyl complexes with FAB. Depending on the cyclopentadienyl ligand steric bulk, instantaneous isobutylene elimination is observed at —75 °C for bis-Cp ligation however for a bis-Cp ligation environment, the cationic species formed is stable at 0 °C yet undergoes clean, revers-... 

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