Simultaneous synthesis, separation, and characterization of metal complexes with monomeric lacunar ligands and dimeric ligands capable of bimetallic coordination

Article abstract of DOI:10.1021/ic50223a020

Two important families of ligands are produced simultaneously in a template-moderated ring-closure reaction. Additional examples of lacunar ligands are reported; these form metal complexes in which a protected cavity suitable for sheltering a small molecule is formed in the vicinity of a coordination site. Simultaneously, dimeric ligands are produced that are capable of binding two metal ions, within macrocyclic moieties, in an approximate face-to-face orientation. The isomeric substances were separated by fractional crystallization or by chromatography. Their structures have been established by combination of definitive and correlative means. Generic distinctions between monomers and dimers are made by high-performance liquid and ion-exchange chromatography, by NMR (proton and ¹³C), and, in some cases, by direct molecular weight determinations on neutral deprotonated derivatives of the nickel(II) complex. Factors favoring monomer and dimer formation are discussed. The monomeric species are the main subject of this paper. ¹³C NMR show that most of the lacunar complexes have the expected mirror symmetry. Electrochemistry shows that the electron density at the metal ion is insensitive to the nature of the bridge but that substituents can cause alterations in electon density. Thus steric and electronic effects of variations in ligand can be applied separately to the interactions of small molecules such as O₂ or CO with coordinated metal ions. The ligands have been separated from nickel(II) and made available for coordination to other metal ions.