Kinetic instability of boron heterofullerenes

Although boron heterofullerenes are produced abundantly in the gas phase, they cannot be isolated in macroscopic amounts. Those with two to six boron atoms were found to have minimum bond resonance energies (min BRE) of less than -0.100 \beta\. All carbon-boron bonds have negative BREs, suggesting that boron atoms markedly destabilize nearby pi bonds. On this theoretical basis, typical boron heterofullerenes are predicted to be kinetically very unstable and chemically very reactive. In contrast, the molecular anions with 60 pi electrons of boron heterofullerenes are predicted to be kinetically much more stable. These anions do not have bonds with large negative BREs. Some of them may be isolable as salts or endohedral complexes. This study constitutes the first attempt to apply the BRE method to heteroconjugated systems.