"The uncontrolled vaporization of graphite that gives C₆₀, C₇₀, and a smattering of higher fullerenes by a process that remains poorly understood is the quintessential irrational synthesis," says Scott, a chemistry professor at Boston College. "If ever luck played a role," it does there.

	SCOTT © 2002 W. MARC BERNSAU
	TRISKELION When this chlorinated hydrocarbon, prepared in Scott's lab, is flash-heated to 1,100 °C in a vacuum, it loses all its chlorine and hydrogen atoms as bond-forming reactions zip it up to form C60. Curved lines indicate where the new bonds form.

Scott and his colleagues have for years been working to devise a rational synthesis of buckminsterfullerene (C₆₀), and last week they reported success. Using a 12-step route consisting almost entirely of classical organic transformations, they have prepared isolable quantities of the soccer-ball-shaped molecule [Science, 295, 1500 (2002)].

The new synthesis provides C₆₀ in no more than 1% yield, so it won't supplant graphite vaporization as a cheap source of buckyballs, Scott says. But the same rational methods may allow chemists to prepare isolable amounts of more complex fullerenes, including those that can't be made by vaporizing graphite.

Margaret M. Boorum, then a graduate student in Scott's lab, started with 1-bromo-4-chlorobenzene and elaborated it in 11 steps to a propeller-shaped chlorinated hydrocarbon (C₆₀H₂₇Cl₃) that resembles a peeled-open buckyball. For the final step, she sent this compound to her former lab mate Hermann Wegner, a graduate student in chemistry professor Armin de Meijere's group at Georg August University in Göttingen, Germany. Using flash vacuum pyrolysis (FVP), Wegner heated the chlorinated precursor to 1,100 °C for a fraction of a second, causing it to lose chlorine and hydrogen atoms in a cascade of rapid-fire ring-closing reactions that stitch its arms together to form a C₆₀ cage.

Scott and coworkers used several methods to establish that C₆₀ is the only fullerene formed in the pyrolysis step. If the chlorinated precursor were to decompose to small fragments that recombine (as in graphite vaporization), one would expect to see higher fullerenes, they point out.

"Scott's achievement is a victory for organic chemists," comments Koichi Komatsu, a chemistry professor at Kyoto University in Japan. He believes this is "the opening of a new era in fullerene science" in which organic chemists, rather than physicists, will take the lead in synthesizing novel fullerenes "in a precisely designed manner with 100% selectivity."

Some chemists who saw an early version of Scott's paper questioned his description of the new C₆₀ synthesis as "rational" because of the pyrolysis step. What is the difference, one remarked, between pyrolyzing graphite in the typical C₆₀ synthesis and pyrolyzing the chlorinated precursor to C₆₀?

In his published paper, Scott points out that a decade of work in his lab has demonstrated the rationality of using FVP to convert, say, a C₃₀ precursor into a bowllike polyarene having the same 30 carbon atoms with two additional C–C bonds. "We don't get random products," he tells C&EN. "We get what we set out to make."

One fullerene chemist, though lauding Scott's paper as "a big achievement" and "beautiful stuff," doubts that the method can be extended to larger fullerenes.

Scott doesn't have those doubts. The key question in his mind is, Of the countless fullerenes that could be pursued using his approach, which one should be the next target? Scott hasn't yet decided. But, he adds, "It will not be C₇₀! We will almost certainly choose one of the higher fullerenes that has never been isolated from graphite vaporization." Other attractive possibilities include a fullerene with a hole in it or a fullerene containing one or more heteroatoms.

"The key to this treasure chest has now been found," Scott says, "and the opportunities are endless."

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Copyright © 2002 American Chemical Society