A Chiral Cyclometalated Iridium Star of David [2]Catenane.

Although circular helicates can be assembled with a range of labile transition-metal centers, solely "chiral-at-metal" examples (i.e., systems without chiral ligands) and heterometallic (i.e., mixed metal systems, racemic or chiral) circular helicates both remain unexplored. Here, we report on the enantioselective synthesis of a heterometallic (Ir2Zn4) hexameric circular helicate and its elaboration into the corresponding triply interlocked Star of David [2]catenane. The relative inertness of Ir(III) enables enantiospecific synthesis of the hexameric circular helicate using chiral-at-metal building blocks. The resulting Star of David [2]catenane, which is a chiral 6-2-1 link, is formed as a single topological enantiomer. The X-ray crystal structure of the (Ir2Zn4)-catenane shows each of the two 95-atom-long macrocycles entwined around the six metal octahedral metal ions and each other, forming a triply interlocked circular double helix. Two PF6- anions reside above and below the central cavity. The Star of David [2]catenane, both with and without coordinated Zn(II) ions, retains the photophysical properties characteristic of cyclometalated Ir(III) complexes. The synthetic strategy opens up new research directions and opportunities for the assembly of other chiral knots, links, and heterometallic circular helicates.