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 A ) 2 (Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,1′-(phenylphosphanediyl)bis{(2 S p )-2-[(1 R )-1-(acetyloxy)ethyl]ferrocene}, [Fe 2 (C 5 H 5 ) 2 (C 24 H 25 O 4 P)], and the other phosphine sulfide is a purely planar–chiral compound (two planar chiral centres), i.e. bis[(2 S p )--2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe 2 (C 5 H 5 ) 2 (C 20 H 17 PS)]. Owing to the stereocentres present, reactions performed on [(Fc A ) 2 (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 A )(Fc B )(Ph)P]. These are {(2 S p )-2-[(1 R )-1-(acetyloxy)ethyl]ferrocen-1-yl}[(2 S p )-2-ethenylferrocen-1-yl]phenyl-( S )-phosphine sulfide, [Fe 2 (C 5 H 5 ) 2 (C 22 H 21 O 2 PS)], [(2 S p )-2-ethenylferrocen-1-yl]{(2 S p )-2-[(1 R )-1-hydroxyethyl]ferrocen-1-yl}phenyl-( S )-phosphine sulfide, [Fe 2 (C 5 H 5 ) 2 (C 20 H 19 OPS)], {(2 S p )-2-[(1 R )-1-(acetyloxy)ethyl]ferrocen-1-yl}{(2 S p )-2-[(1 R )-1-hydroxyethyl]ferrocen-1-yl}phenyl-( R )-phosphine sulfide, [Fe 2 (C 5 H 5 ) 2 (C 22 H 23 O 3 PS)], and {(2 S p )-2-[(1 R )-1-benzylamino)ethyl]ferrocen-1-yl}[(2 S p )-2-ethenylferrocen-1-yl]phenyl-( S )-phosphine sulfide, [Fe 2 (C 5 H 5 ) 2 (C 27 H 26 NPS)]. All of the structures are accessible in one step from known precursors.