Zirconocene-catalyzed dimerization of 1-hexene: Two-stage activation and structure–catalytic performance relationship

• The catalytic performances of 10 different zirconocenes in the dimerization of 1-hexene were compared.
• The zirconocenes were activated via a two-step process.
• The catalytic productivity of ansa-zirconocenes increases with increasing bridge length.
• [(C5H4SiMe2)2O]ZrCl2 is the most selective and productive dimerization catalyst.

The dimerization of 1-hexene was catalyzed by ten zirconocenes. High catalytic productivity was achieved via a two-step activation process, namely, the treatment of the zirconocene with triisobutylaluminum (TIBA) followed by methylaluminoxane (MAO). The zirconocene [(C5H4SiMe2)2O]ZrCl2 (10) exhibits a higher productivity and selectivity to dimer formation than the unsubstituted (C5H5)2ZrCl2 (1) complex. For the ansa-[Z(C5H4)2]ZrCl2 complexes, the catalytic activity increases as the angle between the cyclopentadienyl rings decreases. The dimerization selectivity of 10 reaches 94% when the reaction is performed using Et2AlCl as the chlorine source needed to form the catalytic species. The possible mechanism of selective α-olefin dimerization is discussed.

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