Enantioselectivity of chiral zirconocenes as catalysts in alkene hydro-, carbo- and cycloalumination reactions

Parfenova, Lyudmila V., Berestova, Tatyana V., Tyumkina, Tatyana V., Kovyazin, Pavel V., Khalilov, Leonard M., Whitby, Richard J. and Dzhemilev, Usein M. (2010) Enantioselectivity of chiral zirconocenes as catalysts in alkene hydro-, carbo- and cycloalumination reactions. Tetrahedron: Asymmetry, 21 (3), 299-310. (doi:10.1016/j.tetasy.2010.01.001).

Abstract

Enantioselectivity of chiral Zr catalysts L1L2ZrCl2 (L1 = L2 = 1-neomenthylindenyl (Ind*), (1); L1 = Cp, L2 = Ind* (2); L1 = Cp, L2 = 1-neomenthylindenyl-4,5,6,7-tetrahydroindenyl (Cp*) (3)) in the hydro-, carbo- and cyclo-alumination of alkenes by organoaluminium compounds (OAC) (AlMe3, AlEt3, HAlBui2) has been studied. It was found that OAC type exhibits the most effect on the reactions chemo- and enantioselectivity. The reaction chemo- and enantio-selectivity depend on the catalyst structure and reaction conditions (solvent type, catalyst concentration, temperature) as well. It is shown that lack of asymmetric induction in the reaction of ?-methylstyrene hydroalumination by HAlBui2, catalyzed with complexes 1 or 3, is the result of the formation of Zr hydride complexes of different structure as reaction intermediates. MTPA was used as derivatization reagent for enantiomeric excess estimation and absolute configuration assignment of ?-chiral alcohols obtained after the oxidation and hydrolysis of reaction products. The applicability of MTPA for the assignment of chiral center absolute configuration in ?–ethyl substituted primary alcohols and ?–alkyl-1,4-butanediols was shown.

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Contributors

Author: Richard J. Whitby

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