That, in essence, is what Eiichi Nakamura has done. The University of Tokyo chemistry professor and his coworkers have prepared molecular hybrids of ferrocenes and fullerenes, two families of molecules whose rich scientific legacies have intersected before, but never like this.

In a preliminary communication, the Tokyo chemists describe the synthesis, on a multigram scale, of the first two "bucky ferrocenes" [J. Am. Chem. Soc., 124, 9354 (2002)]. In both, an iron(II) atom is sandwiched between a discrete cyclopentadienyl (Cp) ring and a cyclopentadienide ring that is part of a C₆₀ or C₇₀ cage.

In the C₆₀ hybrid, which is extremely stable, the cyclopentadienide ring coordinated to the iron is isolated from the rest of the cage by five sp³ carbons, each carrying a methyl group. These methyls provide the proper electronic environment to make the pentagon they surround a suitable 6-electron ligand for the metal ion, Nakamura explains. The crown of five methyl groups also makes the pentagon flatter, "so that the pentagon's 2p orbitals and the iron orbitals overlap better with each other."

To make the somewhat less stable C₇₀-ferrocene hybrid, Nakamura's team was able to get away with placing only three methyl groups around the cage's cyclopentadienide ring.

The Japanese team prepares the C₆₀-ferrocene hybrid in a two-step process: First, C₆₀ is methylated in 95% yield on a 10-g scale to give C₆₀(CH₃)₅H. This compound is then heated with [FeCp(CO)₂]₂ in benzonitrile at 180 ºC, producing the bucky ferrocene in 52% isolated yield. A similar synthesis produces the C₇₀-ferrocene hybrid in 31% isolated yield from C₇₀(CH₃)₃H. Nakamura expects to improve the scale of these syntheses.

"The hybrid compound can not only be oxidized reversibly like ferrocene but can also be reduced reversibly like fullerene," the researchers point out in their paper. Since ferrocene itself can only be oxidized, not reduced, the hybrid offers a unique combination of redox properties.

	CHIMERAS Molecular structures of the ferrocene-C60 (above) and -C70 (below) hybrids were determined by X-ray diffraction. COURTESY OF YUTAKA MATSUO, EIICHI NAKAMURA, AND MASAYA SAWAMURA

Nakamura is hopeful that they will be able to synthesize the parent C₆₀ ferrocene--one without any methyl substituents--although calculations by other researchers suggest that the instability of the unsubstituted hybrid will make its synthesis very difficult.

Nakamura says his group can make other bucky ferrocenes as well as other metallocenes, so "the chemistry can be significantly expanded in the future." He also believes the method could be used to construct metallocene structures not only on higher fullerenes but also on the hemispherical end caps of carbon nanotubes.

Nakamura and colleagues demonstrated last year that anionic fullerene derivatives can be made to assemble into vesicles (C&EN, March 12, 2001, page 12). He expects that once the bucky ferrocenes are derivatized with water-soluble groups, they will be amenable to forming redox-tunable vesicles that might be useful for controlled release of drugs or other substances.

The hybrid molecules could also be used as building blocks to construct other types of nanostructures having useful photonic or electronic properties. Chemistry professor Ian Manners of the University of Toronto believes the synthesis of these hybrids "opens up many exciting new research opportunities" and possible applications in materials science.

Not only that, Manners tells C&EN, but "these are beautiful molecules--an inspiring sight for any synthetic chemist!"

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