People - [ Faculty ]

Research Interests:

Our program is pursuing the large-scale synthesis of polynuclear aromatic hydrocarbons (PAHs) with carbon frameworks that can be identified on the buckminster-fullerene C₆₀ surface; we refer to these bowl-shaped PAHs as buckybowls. These novel structures may be involved in host-guest relationships that have potential in the area of catalysis; they represent the end-caps of closed nanotubes and, as such, could serve as as such, could serve as precursors for controlled nanotube synthesis; and they could become an environmental concern if the wide-scale use of fullerenes is ever realized due to potential fragmentation processes of the latter. The simplest example of such a hydrocarbon is corannulene (1), a C₂₀H₁₀ aromatic whose carbon framework represents the polar cap of buckminsterfullerene. Corannulene was the only known member of this family of novel hydrocarbons for over 25 years until our research group produced the next higher homolog with an additional 5-membered ring (2) using Flash Vacuum Pyrolysis. Application of the same methodology led subsequently to even larger buckybowls like semibuckminsterfullerenes 3 and 4.

More recently we have focused on the more practical solution-phase synthesis of these curved-surface PAHs, and we had a major breakthrough with the discovery that we could produce grams of tetrabromocorannulene (6) from a relatively easily prepared precursor 5 with only 15 min reflux in aqueous dioxane containing a little sodium hydroxide. We also developed a high yield conversion of 6 to 1 so we can now conveniently produce large amounts of corannulene. This discovery was featured on the DOE BES Website, and was also the subject of an article in USA Today (June 1, 2001). Hence the ability to produce corannulene on a large scale set the stage for our more recent work which uses 1 as the starting material for the synthesis or large buckybowls. We recently developed practical synthetic routes to corannulyne (7, a reactive dienophile) and to isocorannulenofuran (9, a reactive diene) which serve as synthons for the construction of large molecular assemblies with bowl-shaped subunits. Application of Diels-Alder cycloaddition methodology led to the synthesis of the "buckycatcher" 9, a C₆₀H₂₈ hydrocarbon with two corannulene "pincers" and a tetrabenzocyclooctateraene "tether", capable of forming strong inclusion complexes with fullerenes in the solid state as well as in solution.

Our results provided the first experimental evidence for the importance of concave-convex interactions in the supramolecular chemistry of fullerene carbon cages and buckybowls and were announced in the "Research Highlights" sections of Nature (2007, 446, 360), Chem. Eng. News (2007, 85, 37) and Nature Nanotechnology (2007, March 23).

Publications:

Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242 and references therein.

Sygula, A.; Rabideau, P. W. J. Am. Chem. Soc. 2000, 122, 6323-6324.

Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2005, 7, 4999.

Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2006, 8, 5909.

Sygula, A.; Sygula, R.; Kobryn, L. Org. Lett. 2008, 10, 3927.

Sygula, A.; Fronczek, F. R.; Sygula, R.; Rabideau, P. W.; Olmstead, M. M. J. Am. Chem. Soc. 2007, 129, 3842.

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