Bowl-Shaped Fragments of C_(70) or Higher Fullerenes: Synthesis, Structural Analysis, and Inversion Dynamics

摘要

Most investigations into fullerene chemistry have focused on C_(60), not only owing to its abundance and low cost, but also because of its simple structure. C_(60) is composed of 60 equivalent carbon atoms with two distinct types of C-C bonds. In contrast, C_(70) contains five types of carbon atoms (a-e) with eight types of C-C bonds (I-VIII). The C_(70) molecule can be regarded as two C_(60)-like hemispheres that are connected by a new set of ten carbon atoms (labeled e). Studies of the bowl-shaped subunits of fullerenes may help give an insight into their chemistry. These buckybowls are important because of their interesting physical properties. A very unusual characteristic of these π bowls is their polarity, which is generated by the non-uniform electronic distribution within the curved surface. As a result, they may form polar crystals that exhibit the pyroelectric effect. The chemistry of corannulene (1), sumanene (2), and other bowl-shaped fragments of C_(60) has been intensively investigated in the past two decades. In contrast, the bowl-shaped subunits of C_(70) that contain the unique bond type VIII are almost completely unstudied; to the best of our knowledge, only tetraindenopyrene derivative 3 has been reported. Theoretical analysis has revealed that 3 is not a rigid molecule, and its bowl-to-bowl inversion barrier is only 0.33 kcalmol~(-1). Compounds 9 (Scheme 1) are ideal prototypes for investiga- tion because they contain all the types of carbon atoms that are in C_(70) and are also fragments of many higher fullerenes, including C_(76), C_(78) and C_(84). This investigation presents the synthesis, structures, and physical properties of new bowl-shaped molecules 9.