Researchers in Spain have developed a highly efficient, surface-catalysed route to fullerenes. Unlike traditional methods, which lack synthetic control, the new approach allows heteroatoms to be installed at predetermined positions within the buckyball framework.

The Instituto de Ciencia de Materiales de Madrid (CSIC)-based team successfully synthesised both fullerene, C₆₀, and triazafullerene, C₅₇N₃, in near-quantitative yields. Their technique not only allows the rational design of heterofullerene species, but could also be adapted to make functional structures that encapsulate small molecules within the fullerene framework.

'The advantage of this highly efficient process is that by starting with suitable precursors, heterofullerenes and other fullerene species can be obtained in a controlled way,' says Berta Gomez-Lor, joint principal investigator. 'The "secret" is the use of a catalytic surface that is able to spontaneously induce dehydrogenation of the precursor molecule.'

The fullerenes form on a platinum surface © Nature

Fullerene precursor molecules - with heteroatoms pre-installed - were deposited onto an activated platinum 111 surface by vacuum thermal evaporation. Annealing at 750 K triggers complete fullerene formation, with the heteroatoms already in place. Strong molecule-surface interactions prevented significant molecular diffusion off of the surface.

'This is surely a potential route to hetero- and endohedral metallo-fullerenes'says Sho-ichi Iwamatsu of Nagoya University, prominent in the field of open-cage fullerene synthesis. 'However, key challenges remain regarding both bulk synthesis and the potential to practically encapsulate small molecules.'

Gomez-Lor acknowledges a limitation in the bulk quantity of material produced. Initial results have shown successful cyclisation of precursors using activated platinum nanopowder. This technical variation represents significant progress towards synthetic scale-up.

In application, endohedral fullerenes have potential in the field of drug and contrast agent delivery. For this to be achieved, the process described must be able to function efficiently at positive pressures. A move away from the high-vacuum conditions reported is needed for this goal to become a reality. 

'The controlled synthesis of fullerenes and heterofullerenes of specific structure in isolable quantities remains one of the great challenges still facing the synthetic organic chemist,' says Lawrence Scott, a leader in the field of fullerene synthesis. 'I'm confident that such a goal is within reach, and this work represents another milestone along the road that will lead us there.'

Fred Campbell

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