Stereochemical Alignment in Triphospha[3]ferrocenophanes.

A series of triphospha[3]ferrocenophanes of the type Fe(C5 H4 -PtBu)2 PX with X=H, F, Cl, Br, I, NEt2 , tBu has been prepared and characterized by heteronuclear NMR spectroscopy and X-ray crystallography. Despite having three stereogenic centers, the selective formation of a reduced number of diastereomers (either one or two) has been observed for these ferrocenophanes. Theoretical calculations revealed that the inversion of the central stereogenic center inverts the frontier orbital sequence leading to either an iron or a phosphorus centered HOMO depending on the respective diastereomer. CV measurements supported these results. For the all-tert-butyl substituted [3]ferrocenophane Fe(C5 H4 )2 (PtBu)3 a chiral staggered conformation has been found in the solid state which differs substantially from the only other all-organo substituted [3]ferrocenophane, Fe(C5 H4 )2 (PPh)3 .