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A Chiral Cyclometalated Iridium Star of David [2]Catenane

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journal contribution
posted on 05.01.2021, 15:13 authored by David P. August, Javier Jaramillo-Garcia, David A. Leigh, Alberto Valero, Iñigo J. Vitorica-Yrezabal
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.