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

Abstract The 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 cycloalumination of alkenes by organoaluminium compounds (OAC) (AlMe3, AlEt3, HAlBu 2 i ) has been studied. It was found that OAC exhibit the most effect on the reaction chemo- and enantioselectivity. The reaction chemo- and enantioselectivity depend on the catalyst structure and reaction conditions (solvent type, catalyst concentration, temperature) as well. It is shown that the lack of asymmetric induction in the reaction of α-methylstyrene hydroalumination by HAlBu 2 i , catalyzed with complexes 1 or 3, is the result of the formation of Zr hydride complexes of different structures as reaction intermediates. MTPA was used as a derivatization reagent for the enantiomeric excess estimation and absolute configuration assignment of β-chiral alcohols obtained after the oxidation and hydrolysis of the reaction products. The applicability of MTPA for the assignment of the absolute configuration of the stereogenic centre in β-ethyl substituted primary alcohols and β-alkyl-1,4-butanediols is shown.