Ti Group Metallocene-Catalyzed Synthesis of 1-Hexene Dimers and Tetramers

1-Hexene transformations in the catalytic systems L(2)MCl(2)–XAlBu(i)(2) (L = Cp, M = Ti, Zr, Hf; L = Ind, rac-H(4)C(2)[THInd](2), M = Zr; X = H, Bu (i)) and [Cp(2)ZrH(2)](2)-ClAlR(2) activated by MMAO-12, B(C(6)F(5))(3), or (Ph(3)C)[B(C(6)F(5))(4)] in chlorinated solvents (CH(2)Cl(2), CHCl(3), o-Cl(2)C(6)H(4), ClCH(2)CH(2)Cl) were studied. The systems [Cp(2)ZrH(2)](2)-MMAO-12, [Cp(2)ZrH(2)](2)-ClAlBu(i)(2)-MMAO-12, or Cp(2)ZrCl(2)-HAlBu(i)(2)-MMAO-12 (B(C(6)F(5))(3)) in CH(2)Cl(2) showed the highest activity and selectivity towards the formation of vinylidene head-to-tail alkene dimers. The use of chloroform as a solvent provides further in situ dimer dimerization to give a tetramer yield of up to 89%. A study of the reaction of [Cp(2)ZrH(2)](2) or Cp(2)ZrCl(2) with organoaluminum compounds and MMAO-12 by NMR spectroscopy confirmed the formation of Zr,Zr-hydride clusters as key intermediates of the alkene dimerization. The probable structure of the Zr,Zr-hydride clusters and ways of their generation in the catalytic systems were analyzed using a quantum chemical approach (DFT).