Preparation of ansa-metallocenes for production of poly(α-olefin) lubricants

Abstract

An ansa-zirconocene bearing methyl substituents at all positions adjacent to the bridgehead [(–C(Ph)HC(Ph)H–)(η⁵-2,5-Me₂C₅H₂)₂ZrCl₂] (4) was prepared in high yields (78%) through the reductive dimerization of 1,4-dimethyl-6-phenylfulvene utilizing ZrCl₂·DME generated in situ. The structure of 4 was subsequently confirmed using X-ray crystallography. 4 exhibited excellent catalytic performance with regard to 1-decene oligomerization, which was carried out with the intention of preparing lubricant base stocks. High activities (21 × 10⁶ g mol⁻¹ Zr h⁻¹ activity; TON = 150 000; TOF = 42 s⁻¹) were observed at temperatures as high as 120 °C and the oligomer distribution was appropriate for lubricant application. The simulated distillation (SIMDIS) data confirmed that a wide range of oligomers were formed, ranging from the dimer (2-mer) to 20-mer. A minimal amount of the dimer and oligomers larger than the 10-mer was formed (13 and 25 wt%, respectively). Alternatively, a typical unbridged complex such as (η⁵-nBuC₅H₄)₂ZrCl₂ primarily produced dimers (54 wt%), whereas the ansa-zirconocene (EBI)ZrCl₂ primarily produced oligomers larger than 10-mer (62 wt%). The methyl substituents at the positions adjacent to the bridgehead in 4 played a significant role in the catalytic performance.