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 [(FcA)2(Ph)P], one of which contains four stereogenic centres (two C chiral and two planar chiral centres), i.e. 1,10-(phenylphosphanediyl)bis{(2Sp)-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[(2Sp)-2-ethenylferrocen-1-yl]phenylphosphane sulfide, [Fe2(C5H5)2(C20H17PS)]. Owing to the stereocentres present, reactions performed on [(FcA)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 [(FcA)(Fc B)(Ph)P]. These are {(2Sp)-2-[(1R)-1-(acetyloxy)ethyl]ferrocen-1-yl}[(2Sp)-2-ethenylferrocen-1yl]phenyl-(S)-phosphine sulfide, [Fe2(C5H5)2(C22H21O2PS)], [(2Sp)-2-ethenylferrocen-1-yl]{(2Sp)-2-[(1R)-1-hydroxyethyl]ferrocen-1-yl}phenyl-(S)-phosphine sulfide, [Fe2(C5H5)2(C20H19OPS)], {(2Sp)-2-[(1R)-1-(acetyloxy)ethyl]ferrocen-1yl}{(2Sp)-2-[(1R)-1-hydroxyethyl]ferrocen-1-yl}phenyl-(R)-phosphine sulfide, [Fe2(C5H5)2(C22H23O3PS)], and {(2Sp)-2-[(1R)-1-benzylamino)ethyl] ferrocen1-yl}[(2Sp)-2-ethenylferrocen-1-yl]phenyl-(S)-phosphine sulfide, [Fe2(C5H5)2(C27H26NPS)]. All of the structures are accessible in one step from known precursors.

Automated summary

In the course of a synthetic project on cyclic diferrocenylphosphines, planar-chiral diferrocenyl compounds were obtained as precursors for subsequent cyclization. The crystal structures of two symmetric compounds were reported, one containing four stereogenic centers and the other being a purely planar-chiral compound. Reactions performed on these compounds strongly favored one ferrocene unit over the other due to diastereoselectivity, demonstrating the impact of stereochemistry on reactivity.