Inclusion Complexes Involving a Novel Ligand Superstructure: Dioxygen Adducts and Other Derivatives of Retro-Bridged Cyclidene Iron, Cobalt, and Nickel Complexes

New iron(II) and cobalt(II) dioxygen carriers have been synthesized with a novel family of retro-bridged lacunar cyclidene ligands (structure V) by consecutive template reactions. NMR and ESR spectroscopy, electrochemistry, and equilibrium studies have been applied to the characterization of the new dioxygen carriers. The cobalt complexes unambiguously demonstrate steric control of dioxygen affinity while the iron(II) complexes exhibit both greater dioxygen affinities than previously reported iron(II) lacunar cyclidene complexes and surprisingly moderate sensitivity toward autoxidation. By combining the new retro-bridge with the previously known bridging reaction, both lacunar (structure VI) and vaulted (structure VII) doubly bridged cyclidene complexes of nickel(II) have been prepared. The X-ray crystal structure determination of [Ni{(CH₂)₈(CH₂pipz)₂(3,6-dur)[16]cyclidene)](PF₆)₂*CH₃CN is reported and the results applied to the understanding of the chemistry of the unusual compound: orthorhombic, space group Pnap₁; cell parameters a = 18.863 (4) A, b = 19.822 (3) A, c - 13.761 A, Z = 4.