The nickel (II) complex of the macrocyclic ligand 7,16-dihydro-6,8,15,17-tetramethyldibenzo{b,i}{1,4,8,11}-tetraazacyclotetradecinato (abbreviated Ni TMTAA) undergoes an oxidative dimerization reaction at the 7,16-positions. The complexes of cobalt (III) and other early transition metals are stable to this reaction. In order to study the factors that govern the course of this reaction the characteristics of the oxidized species were investigated. To stabilize the ligand to the coupling reaction to allow spectroscopic observation of the oxidized complexes, the 7 and 16 positions were encumbered by attachment of benzoyl groups. The nickel (II) and cobalt (III) complexes of the disubstituted ligand were electrochemically oxidized and studied via ESR and visible spectroscopy. The oxidized nickel complex is characterized as a distinctive 6-coordinate Ni(III) species in strongly coordinating media. In weakly to moderately coordinating solvents the oxidized compound is 4 or 5 coordinate and is intermediate between a metal-based and a ligand-based radical. The oxidized cobalt compound is predominately a ligand-based radical with a ('59)Co hyperfine of only 13 G. A mechanism for the dimerizaton based on the inhibitory effects of axial ligands is offered to account for the large stability differences between the oxidized nickel and cobalt complexes of the unsubstituted ligand. / In a related study, the sensitivity of anodic redox processes of Ni TMTAA to substitution on the macrocyclic ligand was investigated. A number of complexes derived from three patterns of substitution were prepared. Nine previously unreported compounds have been synthesized. The E(, 1/2) values of the first oxidation wave were measured by cyclic voltammetry. The substitution sensitivities of this process were quantitated by the Hammett equation and expressed in terms of (rho) values. The (rho) values obtained are discussed and compared to similar studies with other tetraaza macrocyclic complexes including metalloporphyrins. / The synthetic methodology developed for the substituted Ni TMTAA complexes was exploited for the preparation of a "capped" macrocyclic ligand. The iron(II) complexes of such a ligand have potential applications to reversible oxygenation studies. The synthesis and prelimary characterization of the nickel(II) complex is reported. There are some indications that the isolated compound may be in fact a cofacial dimeric species rather than a monomer. / Source: Dissertation Abstracts International, Volume: 43-07, Section: B, page: 2204. / Thesis (Ph.D.)--The Florida State University, 1982.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74904 |
| Contributors | SIDDALL, THOMAS LYMAN., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 139 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
Page generated in 0.0019 seconds