Reaktion oxygenierter Kobalt (II)-Komplexe. XII. Über einen binuclearen μ-Peroxodikobalt (III)-Komplex mit makrocyclischem Brückenring

Reactions of oxygenated cobalt(II) complexes. XII. A binuclear μ-peroxodicobalt(III) complex with a macrocyclic bridging ring

1 XI: siehe 1].

Singly bridged (tren) (NH₃) CoO₂(NH₃) (tren)]⁴⁺ reacts with excess tren by replacement of NH₃ in cis-position to the peroxo group and formation of a new type of doubly bridged μ-peroxo complex. An X-ray structure determination of (tren)-Co(O₂, tren)Co(tren)] (ClO₄)₄ · 2 H₂O showed that the additional tren forms a macrocyclic bridging ring. The conformation of the CoOOCo group is transoid with a dihedral angle of 20°. The crystals are monoclinic with space group P2₁/c. The lattice constants are a = 9,798, b = 26,385, c = 16,385 Å, β = 110,2° with four formula units in the cell. The final R value is 0,124. ClO anions are disordered. The reactions of (tren)Co(O₂, tren)Co(tren)]⁴⁺ in aqueous solution are compared with those of (tren) (NH₃) CoO₂Co (NH₃tren)]⁴⁺. In acidic solution the new complex mainly decomposes to Co^II and O₂. In alcaline medium the bridging tren is replaced by an OH bridge, forming the well characterized doubly bridged (tren)-Co(O₂, OH)Co(tren)]³⁺. Differing from the singly bridged bis (ammino) complex, the reactions of which show no pH dependency at all, the decomposition of the tren bridged complex is H⁺-catalyzed. The kinetic data have been interpreted as (i) preceding fast protonation step which is followed by a conformational change of the bridging ring, (ii) acid hydrolysis of a Co-μ-tren bond and (iii) fast cleavage of the Co-OO bond which is labilized by coordinated H₂O.