Synthesis,structures and reactivities of bis(triarylmethylium) dications and related diboranes

Abstract

The primary goal of the research described in this thesis concern the synthesis, characterization and study of 1,8-bis(diarylmethylium)naphthalenediyl dications. Such dications have been prepared from the corresponding diols and have been fully characterized. Single crystals X-ray diffraction studies indicate that the two cationic centers of these derivatives are separated by 3.0 - 3.1 ??. The enforced proximity of the cationic centers intensifies the electron deficiency of these derivatives which behave as strong organic oxidants. As indicated by cyclic voltammetry, these dications undergo a two-electron reduction to afford the corresponding acenaphthenes. The newly formed C-C bond which links the former methylium are remarkably long (1.628-1.706 ??.) and can, in some instances, be oxidatively cleaved in the presence of acids. These dications can also be reduced chemically by reducing reagent, such as hydride, chloride, bromide and iodide. Remarkably, the reaction of 1,8-bis(diphenylmethylium)naphthalenediyl dication with fluoride anion results in the formation of a mono fluorinated cation which features an unsymmetrical C-F?C bridge between the former methylium centers. As indicated by 1H NMR spectroscopy, the structure of this cation is fluxional with the fluorine atom oscillating between the former methylium centers. Finally, this thesis also deals with the synthesis and study of 4,6-bis(dimesitylboryl)dibenzofuran and isoelectronic dications.