Catalytic activity and chemoselectivity of zirconocenes in the reaction of alkenes with AlEt3 were evaluated. NMR study of the reaction between L2ZrCl2 and AlEt3 showed the formation of various bimetallic intermediates.

The activation of the systems (MeCp)2ZrCl2-HAlBu i 2-alkene by (Ph3C)[B(C6F5)4] resulted in the selective formation of head-to-tail dimers in up to 89-96% yields. A study of the reaction of (MeCp)2ZrCl2 with HAlBu i 2 ([Zr] 3) for which diffusion coefficients and hydrodynamic radii were estimated using the diffusion ordered spectroscopy (DOSY). Compound 3 is characterized by a triplet signal at δH −6.05 ppm and a doublet at δH −1.02 ppm ( 2 J=17.5 Hz) in 1 H NMR spectrum. Moreover, the signals correlated in the COSY HH and NOESY spectra. The NOESY spectrum of this system exhibited cross peaks between the upfield signals of hydride atoms and the downfield signals of Cp ring protons at δН 5.08 (δС 104.9 ppm), 5.12 (δС 112.9 ppm), 5.64 (δС 107.1 ppm) and 5.48 (δС 108.5 ppm) and a singlet of Me group protons at 1.83 (δС 15.0) ppm. Complex 2 is characterized by a diffusion coefficient within 1.96•10 -9 -2.40•10 -9 m 2 /s and diameter of particles 3.92-4.03 Å (calculated according to the modified Stokes-Einstein equation). The addition of the activator (Ph3C)[B(C6F5)4] leads to the formation of a heavy adduct 3 with a diffusion coefficient of 2.06•10 -10 m 2 /s and a particle diameter of 19.1 Å, respectively. The reaction of hexene-1 with a mixture containing complex 3 in the NMR tube provided the formation of a vinylidene dimer within 60 min. Thus, intermediate 3 was proposed as a precursor of catalytically active centers of the dimerization reaction.