Metal (Co, Fe) tribenzotetraazachlorin-fullerene conjugates: Impact of direct π-bonding on the redox behaviour and oxygen reduction reaction

Novel hexabutylsulphonyltribenzotetraazachlorin-fullerene (C-60) complexes of iron (FeHBSTBTAC-C-60) and cobalt (CoHBSTBTAC-C-60) have been synthesized and their electrochemistry and oxygen reduction reaction (ORR) compared with their octabutylsulphonylphthalocyanine analogues (FeOBSPc and CoOBSPc). It is proved that electron-withdrawing substituents (-SO2Bu and C60) on phthalocyanine macrocycle exhibit distinct impact on the solution electrochemistry of these metallophthalocyanine (MPc) complexes. The more electron-withdrawing C-60 substituent suppressed ORR compared to the -SO2Bu in alkaline medium. FeOBSPc showed the best ORR activity involving a direct 4-electron mechanism, a rate constant of similar to 1 x 10(8) cm(3) mol(-1) s(-1) and a Tafel slope of -171 mV dec(-1). (C) 2009 Elsevier B.V. All rights reserved.