Regioselective Electrosynthesis Of[60]Fullerene Tetra-Adducts

Recently, fullerene tetra-adducts have attracted increasing attention due to their potential applications in many different areas such as materials science and biological science. However, since the preparation of fullerene tetra-adducts is usually complicated by the formation of various regioisomers, considerable efforts have been made to control the regioselectivity of multiple addition reactions. As a novel approach to achieve high regioselectivity, electrosynthesis is simple and efficient, and it has developed rapidly in recent years. It has been shown that electrochemically generated fullerene anions, especially singly bonded fullerene dianions, can be readily prepared and used as building blocks in the regioselective synthesis of fullerene tetra-adducts.During our recent study on the electrochemical property of a [60]fulleroindoline, we were surprised to find that by receiving two electrons it was converted to a singly bonded fullerene dianion. Subsequently, a1,2,3,4-tetrahydrofullerene and a series of rare1,2,3,16-functionalized fullerene derivatives were prepared. Fortunately, we got the X-ray crystallographic proof of the1,2,3,16-configuration for the first time. To our delight, we also found that the regioselectivity of the reaction involving dianionic [60]fulleroindoline depended on the size of the electrophile. When the dianion was treated with trifluoroacetic acid (TFA), a1,2,3,4-tetrahydrofullerene derivative with two fullerenyl protons was obtained selectively. In contrast, when much bulkier benzyl bromide or ethyl bromoacetate was used instead of TFA, the addition pattern of the product was different. Correspondingly, an unusual but interesting1,2,3,16-tetrahydrofullerene derivative with a fullerenyl proton and a RCH2(R=Ph, COOEt) group on the fullerene skeleton was generated with high regioselectivity. Additionally, when the dianion was treated with strong base NaH and RCH2Br (R=Ph, COOEt) in a largely excessive amount, a1,2,3,16-tetrafunctionalized fullerene derivative with two RCH2groups on the fullerene sphere was obtained selectively. Much to our satisfaction, the origin for the regioselective formation of the1,2,3,4-and1,2,3,16-adducts was elucidated by theoretical calculations.