Skeletal Transformation of a Classical Fullerene C₈₈ into a Nonclassical Fullerene Chloride C₈₄Cl₃₀ Bearing Quaternary Sequentially Fused Pentagons

A classical fullerene is composed of hexagons and pentagons only, and its stability is generally determined by the Isolated-Pentagon-Rule (IPR). Herein, high-temperature chlorination of a mixture containing a classical IPR-obeying fullerene C88 resulted in isolation and X-ray crystallographic characterization of non-IPR, nonclassical (NC) fullerene chloride C84(NC2)Cl30 (1) containing two heptagons. The carbon cage in C84(NC2)Cl30 contains 14 pentagons, 12 of which form two pairs of fused pentagons and two groups of quaternary sequentially fused pentagons, which have never been observed in reported carbon cages. All 30 Cl atoms form an unprecedented single chain of ortho attachments on the C84 cage. A reconstruction of the pathway of the chlorination-promoted skeletal transformation revealed that the previously unknown IPR isomer C88(3) is converted into 1 by two losses of C2 fragments followed by two Stone-Wales rearrangements, resulting in the formation of very stable chloride with rather short C-Cl bonds.