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

Six new homochiral diferrocenyl derivatives have been synthesized, one of which is purely planar–chiral. Even if the two diferrocene subunits are identical, they are distinguished due to their positions relative to the substituents at the phospho­rous prochiral centre.

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{(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocene}, [Fe₂(C₅H₅)₂(C₂₄H₂₅O₄P)], and the other phosphine sulfide is a purely planar–chiral com­pound (two planar chiral centres), i.e. bis[(2S_p)--2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₇PS)]. 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 {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₁O₂PS)], [(2S_p)-2-ethenylferrocen-1-yl]{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₀H₁₉OPS)], {(2S_p)-2-[(1R)-1-(acet­yloxy)eth­yl]ferro­cen-1-yl}{(2S_p)-2-[(1R)-1-hy­droxy­eth­yl]ferrocen-1-yl}phenyl-(R)-phos­phine sulfide, [Fe₂(C₅H₅)₂(C₂₂H₂₃O₃PS)], and {(2S_p)-2-[(1R)-1-benzyl­amino)­eth­yl]ferrocen-1-yl}[(2S_p)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe₂(C₅H₅)₂(C₂₇H₂₆NPS)]. All of the structures are accessible in one step from known precursors.