Fullerene-acene chemistry: Part I Studies on the regioselective reduction of acenes and acene quinones; Part II Progress toward the synthesis of large acenes and their Diels-Alder chemistry with fullerene
Date of Award
Program or Major
Doctor of Philosophy
Glen P Miller
The regioselective reduction of acenes and acene quinones has been studied. Using hydriodic acid (HI) in acetic acid (HOAc) as reductant, it was found that acenes smaller than five rings reduce in a regioselective fashion. It was also found that phenyl substituted acenes with as many as seven rings will reduce regioselectively to leave the internal terphenyl moieties intact. In the cases of 6,13-diphenylpentacene and 5,7,12,14-tetraphenylheptacene quinone, reduction occurs at alternating rings such that the end rings and the internal terphenyl moieties were left intact. When large unsubstituted acenes are reduced, the reduction occurs with no selectivity resulting in complex mixtures of variously hydrogenated isomers. In all cases, the reduced acenes or acene quinones were more stable and more soluble than either the acenes or acene quinones themselves. These hydrogenated species could be stored and handled under ambient conditions and readily dehydrogenated to the desired acenes on demand.
In addition to the reduction of acenes and acene quinones, the syntheses of various large acenes and their Diels-Alder chemistries with fullerene were studied. These studies were focused toward preparing multiple fullerene adducts as precursors to cyclacenes. The synthesis of nine- and eleven-ring acenes was undertaken and was found to be quite difficult. Concurrently, the synthesis of end-functionalized acenes was undertaken in order to prepare cyclacenes via a complimentary supramolecular approach. Three methyl substituted pentacenes were prepared, along with their fullerene adducts. Additionally, work toward preparing pentacenes with different end functionalities was undertaken.
Finally, a flexible fullerene bisadduct was prepared via reaction of tetrakis(bromomethyl) terphenyl and fullerene in the presence of iodide. This bisadduct maps directly onto the previously prepared bisfullerene adduct of 6,13-diphenylpentacene. While this adduct would in theory have conformational flexibility, it was found to exist solely in the cis conformation on the NMR time scale, suggesting that internal pi-pi stacking between fullerenes locks the molecule into the cis conformation.
Athans, Andreas John, "Fullerene-acene chemistry: Part I Studies on the regioselective reduction of acenes and acene quinones; Part II Progress toward the synthesis of large acenes and their Diels-Alder chemistry with fullerene" (2007). Doctoral Dissertations. 363.