Open-Cage Fullerenes: Synthesis, Structure, and Molecular Encapsulation

The carbon-carbon bond scission of the fullerene cage offers an open-cage fullerene derivative having an opening on the fullerene surface. This account summarizes our recent studies on the syntheses of open-cage C60 derivatives as well as their properties of molecular encapsulation. The photochemical rearrangement of the cyclohexadiene derivative of C60 gives bis(fulleroid), the precursor for the cage scission. The photooxygenative carbon-carbon bond cleavage of bis(fulleroid) affords an open-cage diketone derivative having a 12-membered ring. The reaction of the diketone derivative with aromatic hydrazine or hydrazone allows the ring expansion of the orifice by regioselective cage scission to yield a product bearing a 16-membered ring. The orifice in the product is large enough to pass a hydrogen molecule, producing an endohedral hydrogen complex. In the case of the reaction with ortho-phenylenediamine, two carbon-carbon bonds are sequentially cleaved to afford a product having a 20-membered ring orifice. This product spontaneously encapsulates one water molecule to form an endohedral water complex.