Cationic nickel complexes with weakly coordinating counterions and their application in the asymmetric cycloisomerisation of 1,6-dienes

Abstract

The influence of the counterion on cationic nickel catalysts for asymmetric cycloisomerisation of diethyl diallylmalonate (1a) and N,N-diallyltosylamide (1b) is investigated. The activity of the catalysts formed from [Ni(η3-allyl)(η4-cod)]+ salts of weakly coordinating anions in combination with Wilke's azaphospholene ligand decreases in the order [Al{OC(CF3)3}4]- > [B{3,5-(CF3)2-C6H3} 4]- > [Al{OC(CF3)2Ph} 4]- for 1a and [B{3,5-(CF3)2-C 6H3}4]- > [Al{OC(CF 3)2Ph}4]- > [Al{OC(CF 3)3}4]- for 1b, respectively. No significant influence on the enantioselectivity is observed for 1a whereas a marked increase in ee parallel to a decreasing activity is found for the cyclisation of 1b. © 2005 Wiley-VCH Verlag GmbH & Co. KGaA.