The 'weak-link' approach to the synthesis of inorganic macrocycles and three-dimensional structure

This dissertation details a new synthetic method for preparing of binuclear macrocycles from flexible ligands and transition metal precursors. This synthetic approach makes use of hemilabile ligands to target "condensed" macrocyclic structures comprised of a series of thermodynamically stable small rings bound to metal centers by both weak and strong bonds. Introduction of ancillary ligands that bind to a metal center more strongly than the weakly binding groups of the hemilabile ligands displaces the weak links from the metal centers and opens the "condensed" structures into large homobimetallic macrocyclic ring compounds. Overall yields for these reactions are generally quantitative. The solid-state structures as determined by single crystal X-ray diffraction studies are presented for seven of these macrocycles. Judicious choice of ligand affords extensive tailorability with regard to macrocycle size and cavity hydrophobicity. The metal centers of the macrocycles are coordinatively labile allowing one to use simple ligand substitution reactions to change both the electronic and steric environments around the metal centers. This property has been taken advantage of in two ways: (1) through ligand substitution these macrocycles will bind bifunctional aromatic molecules spanning their internal cavity to formed three-tiered metallocyclophane structures, and (2) combination of these macrocycles with appropriate large bifunctional aromatic molecules leads to formation of three dimensional molecular cylinder structures.;The thermodynamic products of these macrocycle reactions are often mononuclear Rh(I) compounds with bisphosphine eta6-planostool geometries about the metal centers. The solid-state structures of two of these compounds as determined by single crystal X-ray diffraction studies are presented. These compounds are interesting in that they exhibit reversible Rh(I/II) redox chemistry as determined by cyclic voltammetry experiments. Chemical oxidation of one of these complexes ([eta1:eta6:eta 1-(1,4-bis(3-diphenylphosphinopropoxy)-2,3,5,6-tetramethylbenzene)Rh] [BF4]) has resulted in the first isolated and characterized monomeric organometallic Rh(II) complex with two-legged piano stool geometry.