Mechanistic aspects of chemo- and regioselectivity in Cp2ZrCl2-catalyzed alkene cycloalumination by AlEt3

• DFT study on catalytically active site action in alkene cycloalumination was carried out.
• Zirconacyclopropane and [Cp2Zr(μ-Cl)CH2CH2AlEt2] were considered as active sites.
• Olefins react with active sites to give substituted zirconacycles via bis-olefin complexes.
• The alkene structure effect on the reaction chemo- and regioselectivity was explained.

The reactions of styrene and 1-hexene with zirconacyclopropane and the bimetallic five-membered Zr,Al-complex [Cp2Zr(μ-Cl)CH2CH2AlEt2] as catalytically active sites in Cp2ZrCl2-catalyzed cycloalumination of α-olefins with AlEt3 have been studied by DFT quantum chemical methods (PBE/3ζ, B3LYP/VDZ, B3LYP(GD3)/VDZ, M06-2X/VDZ, M06-2X/VTZ//VDZ). It was shown that key intermediates can exist in dynamic equilibrium with each other, and with ClAlEt2 adducts. Comparative analysis was carried out for the energy characteristics of alternative pathways in the reaction of styrene or 1-hexene with the intermediates, implying different orientations of the substrates towards the Zr-C bond. The obtained data were used to elucidate the reasons for the observed dependence of the reaction regioselectivity on the substrate structure and the minor by-products formation. The applicability of M06-2X/cc-pVTZ-PP//M06-2X/cc-pVDZ-PP and PBE/3ζ methods for the description of the available experimental data was shown.

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