Enantiopure Phospha[1]ferrocenophanes: Textbook Examples of Through-Space Nuclear Spin-Spin Coupling

Three enantiopure phospha[1]ferrocenophanes (2^R ) equipped with either a phenyl, an isopropyl, or a tert-butyl group at the bridging phosphorus atom were synthesized by a salt-metathesis approach in isolated yields between 52 and 63 %. The chirality in these strained sandwich compounds stems from the planar-chiral ferrocene moiety, which is symmetrically equipped with two iPr groups adjacent to phosphorus. Surprisingly, all three phospha[1]ferrocenophanes show an uncommon through-space nuclear ¹ H-³¹ P coupling. As a result of the embedded symmetry, these new compounds are ideal examples to differentiate between through-space and through-bond coupling mechanisms in NMR spectroscopy.