SYNTHESIS AND CHARACTERIZATION OF COFACIAL METALLODIPORPHYRINS INVOLVING COBALT AND LEWIS-ACID METALS - NEW DINUCLEAR MULTIELECTRON REDOX CATALYSTS OF DIOXYGEN REDUCTION

The synthesis and physical chemical characterization of a novel family of heterodinuclear cofacial biphenylene- or anthracene-bridged bisporphyrins, (DP)CoM(X), is reported, DP4- being either the anion of 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene, DPB4-, or 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene, DPA(4-), and X = O, OAc, Cl, acac, or OH coordinated to M = Ti, Ga, In, Lu, or Sc. Each complex has been characterized by mass spectrometry, UV-visible, IR, ESR, and H-1 NMR spectroscopies and their catalytic activity toward dioxygen reduction has been studied by electrochemistry. The (DP)CoLn(X)(Ln = Lu, Sc) complexes have been subjected to an extensive study. The efficiency of these derivatives unambiguously demonstrates that the presence of two cobalt centers is not a prerequisite for a good catalytic behavior toward dioxygen reduction via the four-electron process. The second cobalt can be replaced by a cation having a strong Lewis acid character.