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

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)(2)O]ZrCl2 (10) exhibits a higher productivity and selectivity to dimer formation than the unsubstituted (C5H5)(2)ZrCl2 (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 alpha-olefin dimerization is discussed. (C) 2016 Elsevier B.V. All rights reserved.