Experimental and Theoretical Study of Zirconocene-Catalyzed Oligomerization of 1-Octene

Zirconocene-catalyzed coordination oligomerization of higher alpha-olefins is of theoretical and practical interest. In this paper, we present the results of experimental and theoretical study of alpha-olefin oligomerization, catalyzed by (eta(5)-C5H5)](2)ZrX2 1/1' and O[SiMe2(eta(5)-C5H4)](2)ZrX2 2/2' (X = Cl, Me) with the activation by modified methylalymoxane MMAO-12 or by perfluoroalkyl borate [PhNMe2H][B(C6F5)(4)] (NBF) in the presence and in the absence of organoaluminium compounds, Al(CH2CHMe2)(3) (TIBA) and/or Et2AlCl. Under the conditions providing a conventional mononuclear reaction mechanism, 1' catalyzed dimerization with low selectivity, while 2' initiated the formation of oligomers in equal mass ratio. The presence of TIBA and especially Et2AlCl resulted in an increase of the selectivity of dimerization. Quantum chemical simulations of the main and side processes performed at the M-06x/ DGDZVP level of the density functional theory (DFT) allowed to explain experimental results involving traditional mononuclear and novel Zr-Al-1 and Zr-Al-2 mechanistic concepts.