Synthesis and electrochemical investigations of molecular architectures involving C60 and tetraphenylporphyrin as building blocks

A C-60-porphyrin diad 3a has been prepared by connecting a zinc porphyrin and C-60 via nucleophilic cyclopropanation, The fullerene diad as well as the related precursor porphyrins 1a, 2a have been investigated by cyclic and differential pulse voltammetry in dichloromethane. Whereas no oxidation peaks were observed for C-60, all compounds 1a-3a exhibit two successive, quasi-reversible oxidation peaks in terms of an EE mechanism. The peak potentials of all three species almost coincide, due to an oxidation of the porphyrin ring system in all cases. In the cathodic process, on the other hand, the compounds are reduced in quasi-reversible four (C-60), two (1a,2a) and five (3a) one-electron transfers. The first two formal potentials of 3a (resulting from the C-60 moiety) are shifted towards negative potentials by 40 mV, as compared to C-60, which is typical for methanofullerenes. Aside from coulombic effects, there is almost no electronic interaction between the C-60 and porphyrin parts in 3a, Furthermore, a mixed hexaadduct 4 of C-60 with an octahedral addition pattern incorporating a zinc tetraphenylporphyrin has been synthesized.