Dr. Billups’ research has covered a wide variety of areas in organic chemistry, inorganic and materials chemistry. His early work focused on the synthesis and thermal rearrangements of methylenecyclopropenes. The scheme used for these syntheses soon evolved in to a simple straightforward synthesis of cyclopropabenzene.
Application of this chemistry to the synthesis of other cycloproparenes soon followed. Representative compounds that have been synthesized either in the Billups laboratory or elsewhere are illustrated below. Detailed studies on the chemistry of these compounds have been investigated including a determination of structures and strain energies.
As the program evolved, a major focus centered on the synthesis of new molecular systems of theoretical interest. The development of a vacuum gas phase procedure for the synthesis of small ring cycloalkenes using reagents adsorbed on inert surfaces to affect elimination reactions played a major role in this work. This approach allows the reactive species to be isolated at low temperature, and eliminates many of the undesired bimolecular side reactions that would normally be encountered in solution. Energetic compounds can thus be collected readily in cold traps for further chemical studies or spectral characterization. Representative molecules whose syntheses have been accomplished include methylenecyclopropene, spiropentadiene, and spiroheptatriene, 3,3’-bicyclopropenyl, the last (CH6) isomer of benzene to be synthesized, and oxaspiropentane.
X-ray structural parameters of unstable low melting compounds were secured in collaboration with Dr. Roland Boese in Essen, Germany. Collaborative work with Boese and an industrial sponsor led to the nucleation, growth, and structure determination of gas hydrates by X-Ray crystallography. Gas hydrates cause serious problems in long distance natural gas pipelines.
Another area involved studies on the activation of carbon-hydrogen bonds by first row transition metals. For example, photoexcited cobalt atoms were found to insert into the carbon-hydrogen bonds of methane to yield CH3CoH. This same species can be microsynthesized and characterized using FTIR spectroscopy by cocondensing the metal with CH2N2, H2, and argon at 11 K. Photolysis of CH3CoH using 400 nm light leads to extrusion of the metal with the formation of the spectroscopically detectable Co(CH4) s-complex 2 shown to have C3v symmetry. Photolysis of this complex using a UV source regenerates the insertion product CH3CoH. Deuterium labeling studies have shown that the methane rotates freely on the cobalt. These studies were carried out in collaboration with the late Professor John Margrave and his coworkers.
Billups’ research has involved all of the major allotropes of carbon. For example, the first reaction of the fullerene C60, a Birch reduction, carried out in collaboration with Marco Ciufolini gave C60H36. 3He NMR spectroscopy played an important role in the characterization of these materials. These studies were carried out in collaboration with Professor Martin Saunders at Yale University.
Current studies have focused on the development of routes to soluble carbon nanotubes and graphene. Studies on the sidewall functionalization of carbon nanotubes by reductive alkylation gives nearly complete exfoliation, without sonication, when dodecyl groups are added to the nanotubes.
Graphene/graphite has also been functionaized under an expansive set of conditions. Water-soluble graphene proved to be especially interesting since functionalization of graphite by the addition of phenyl groups followed by sulfonation gave material that exhibited high solubility in water (2.1mg/mL).
STM images show that the phenyl groups add to the edges of the graphene. This leaves the basal plane free of defects. The STM image shows a single layer of graphene attached to the adjacent larger structure. The exfoliated graphene edges show a 40% higher roughness compared to that of bulk graphite. The defect free STM image of the area inside the white box of Figure a is shown in Figure b.
We also have significant new results with anthracite coal. Studies have been carried with anthracite coal from the Mammoth seam that is located Schuylkill county Pennsylvania. Reduction of anthracite by electron transfer from either lithium or sodium in liquid ammonia yields a salt that can be alkylated by 1-iodododecane to yield nanocoal that is partially soluble in common organic solvents. NMR indicates that the dodecyl groups are attached to the edges of the aromatic ring systems, with many of the dodecyl groups extending into void spaces. The sample of anthracite has been shown by Boris Yakobson to be replete with dislocations. Two edge and two circular dislocations were identified by high resolution transmission electron microscopy.