Synthesis and characterization of enantiopure planar-chiral phosphorus-linked diferrocenes.

In the course of an ongoing synthetic project on cyclic diferrocenylphosphines, we obtained a group of planar-chiral diferrocenyl compounds useful as precursors for subsequent cyclization. Here we report the crystal structures of two symmetric compounds [(Fc)(Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,1'-(phenylphosphanediyl)bis{(2S)-2-[(1R)-1-(acetyloxy)ethyl]ferrocene}, [Fe(CH)(CHOP)], and the other phosphine sulfide is a purely planar-chiral compound (two planar chiral centres), i.e. bis[(2S)--2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe(CH)(CHPS)]. Owing to the stereocentres present, reactions performed on [(Fc)(Ph)P]-type compounds strongly favour one ferrocene unit over the other due to diastereoselectivity. Furthermore, we present four related structures where the ferrocene units are not identical [(Fc)(Fc)(Ph)P]. These are {(2S)-2-[(1R)-1-(acetyloxy)ethyl]ferrocen-1-yl}[(2S)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe(CH)(CHOPS)], [(2S)-2-ethenylferrocen-1-yl]{(2S)-2-[(1R)-1-hydroxyethyl]ferrocen-1-yl}phenyl-(S)-phosphine sulfide, [Fe(CH)(CHOPS)], {(2S)-2-[(1R)-1-(acetyloxy)ethyl]ferrocen-1-yl}{(2S)-2-[(1R)-1-hydroxyethyl]ferrocen-1-yl}phenyl-(R)-phosphine sulfide, [Fe(CH)(CHOPS)], and {(2S)-2-[(1R)-1-benzylamino)ethyl]ferrocen-1-yl}[(2S)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe(CH)(CHNPS)]. All of the structures are accessible in one step from known precursors.