Synthesis of a bis-macrocycle containing two back-to-back rigidly connected 1,10-phenanthroline units as a central core and its incorporation in a handcuff-like catenane

A bis-macrocycle containing two back-to-back connected 1,10-phenanthroline chelates has been prepared. The synthetic strategy involves the preparation of a monocyclic precursor consisting of a 1,10-phenanthroline-5,6-dione fragment incorporated in a 30-membered ring. This important intermediate has been prepared via two distinct routes, both strategies relying on the use of a ketal as a 1,2-dione protective group. A four-component condensation reaction between two molecules of the macrocyclic dione and two equivalents of ammonia (used in large excess) in the presence of a reducing agent (Na2S2O4) leads to the desired bis-ring in good yield. The most direct synthetic route allows preparation of the bis-macrocycle in seven steps from 1,10-phenanthroline in an overall yield of 14%. Using the now well-established gathering and threading effect of copper(I), a doubly threaded species could be obtained in quantitative yield, in which each ring of the bis-macrocycle is threaded by a molecular string. These fragments bear terminal allylic groups, which are used to prepare the final catenane by performing a double ring-closing metathesis reaction. This final cyclisation reaction is high yielding and affords the desired catenane consisting of a bis-macrocycle of which the two cyclic units are threaded by a large ring. The compound has been fully characterised by classical techniques. Electronic spectroscopy and electrochemical measurements suggest that the two copper complex subunits do not interact electronically, in spite of the aromatic nature of the bridging ligand between the two metal centres.