Trans Effect of Different Coordinated Atoms of Planar Chiral Ferrocene Ligands with the Same Backbone in Palladium−Catalyzed Allylic Substitutions

A series of planar chiral P,S-, P,(CN)-, and S,(CN)-bidentate ferrocenyl ligands 4, 5, 8,
and 9 with the same central and planar chiralities were prepared from the commercially
available starting material N,N-dimethyl-(S)-α-ferrocenylethylamine. A Pd-catalyzed asymmetric allylic alkylation reaction was used as a model reaction to study the trans effect of
the coordination atoms by these ligands. On the basis of the reaction results and the study
of X-ray diffraction as well as 1H and 13C NMR spectra of the complexes (12−15), the sequence
of the trans effect was established as CN > P > S, which was supported by molecular
modeling at the PM3 level.