Binaphthyl Schiff base complexes of palladium(II). Structures and reactivities toward alkene epoxidation

Abstract

Palladium(II) binaphthyl Schiff base complexes [PdII(L)](1: H2L =(racemic or fl)-2,2′-bis(3,5-dichloro-2-hydroxybenzylideneamino)-l, 1′-binaphthyl(H2L2);2: H2L =(A)-2,2′-bis(3,5-dichloro-2-hydroxylbenzylideneamino)-5,5′,6, 6′,7,7′,8,8′-octahydro-l,1′-binaphthyl(H 2L3)) were prepared from sequential reactions of H2L with sodium methoxide and palladium(II) acetate in methanol in about 70% yields. Both complexes 1 and 2 have been characterised by X-ray crystallography as well as 1H NMR, IR, UV/VIS and MS spectroscopy. The structures of 1 and 2 feature a pseudo planar N2O2 arrangement with the Schiff base ligands adopting a stepped conformation, in contrast to the non-planar N2O2 geometry usually observed for this type of Schiff base bound to various metal ions. The catalytic behaviour of complexes 1 and 2 toward asymmetric epoxidation of styrènes was investigated. With 2 as a catalyst, a 71% ee was obtained for the epoxidation of p-fiuorostyrene by 1BuOOH. © The Royal Society of Chemistry 2000.