Conformationally-locked metallomacrocycles—prototypes for a novel type of axial chirality

A series of ditopic ligands incorporating two 2,2′:6′,2″-terpyridine (tpy) metal-binding domains linked to a central naphthalenediyl core by ethyleneoxy chains of various lengths have been prepared and their iron(II) complexes prepared. The major thermodynamic products of complexation are ferracycles of [1 + 1], [2 + 2] or [3 + 3] stoichiometry. In the case of the [1 + 1] complexes, the linker between the two tpy domains is spatially restricted and the cations exhibit chirality associated with the conformation about the central N–Fe–N bonds. The dynamic processes by which the enantiomeric forms interconvert are investigated in the presence of chiral anions by NMR and circular dichroism spectroscopy making use of the Pfeiffer effect. We have shown that ditopic bis(2,2′:6′,2″-terpyridine) ligands give rise to conformationally restricted complexes with iron(II) centres. The absolute configuration of the cations in the diastereomeric ion pairs obtained through the Pfeiffer effect has been calculated using TDDFT methods.