Ferrocene-Based Olefin Polymerization Catalysts: Activation, Structure, and Intermediates

This paper describes abstraction of a benzyl group from the Zr dibenzyl complex 1,1‘-Fc(NSiMe3)2]ZrBn2 (1) using B(C6F5)3 and [Ph3C][B(C6F5)4] (TB). In both cases, clean formation
of the corresponding cationic monobenzyl species LZrBn+ (L = 1,1‘-Fc(NSiMe3)22-) was
observed by NMR spectroscopy. In the case of [LZrBn][BnB(C6F5)3] (2), an X-ray crystal
structure determination confirmed an η6 coordination of the borate benzyl group to the
cationic Zr center. Reaction of this complex with 1 equiv of C2H2 or RCCR (R = Me, Ph)
proceeded with rapid single insertion of the olefin or acetylene into the Zr−carbon σ-bond.
With ethylene or 2-butyne further insertions occur more slowly and longer chains were
obtained upon addition of more monomer. Activation of 1 with TB leads to an active ethylene
polymerization catalyst, producing 102 g of PE mmol-1 atm-1 h-1. Compound 2 reacted with
CH2Cl2 to form the dimeric [LZrCl2]2, which was characterized crystallographically.