Structure of the Dicobalt “Face-to-Face” Porphyrin with Two Four-Atom Amide Bridges: Co₂(FTF4)·CH₃OH·1.6CH₂Cl₂

The structure of the dicobalt “face-to-face” porphyrin with two four-atom amide bridges [Co₂(FTF4)] has been determined by single-crystal X-ray diffraction methods. This compound is the first synthetic molecule that catalyzes the direct four-electron reduction of O₂ to H₂O in acidic media. The Co₂(FTF4) molecule exhibits crystallographically imposed twofold symmetry, and hence the amide bridge is disordered. The crystal is composed of only one enantiomeric pair, d, 1-anti. The two porphyrin rings of the compound are stacked almost exactly over each other; the shear displacement of the two metal centers is only 0.13 Å. These two porphyrin rings, interplanar distance 3.54 Å, are twisted by approximately 40° with respect to each other. The cobalt atom is slightly displaced out of the mean porphyrin plane toward the diporphyrin cavity and the Co-Co distance is 3.417 (4) Å. This structure is compared with those of other cofacial porphyrin dimers. Possible O₂ binding modes in this compound are also discussed. Crystallographic data: monoclinic, C2/c, Z = 4, a = 14.365 (9) Å, b = 14.923 (10) Å, c = 27.182 (18) Å, β = 95.94 (1)°, V = 5795 ų at -150 °C, 2971 unique data, 215 variables, R(F) (F_o² > 3σ(F_o²)) = 0.084.