Synthesis and stability of new hexaazamacrocyclic dinuclear cobalt complexes and its oxidation reactions

Homodinuclear cobalt complexes with a new 26-membered unsymmetric macrocyclic ligand: 3,6,10,18,22,25,-hexaaza-31,32dihydroxy-14,29-dimethyl-tricyclo[25,3,1,1,(11,17)] dotriaconta-1(30),12,14,16(32),27,28-hexaene (L or BTBP), have been synthesized and characterized with elemental analysis, FAB-MS and X-ray. The ligand maintains preorganized dinuclear integrity for cobalt(II) complexes, while facilitating the formation of non-bridged dicobalt centers. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear complexes are formed with Co(II) from pH 2 through 12 in aq. solution. The stability constants and species distribution as a function of pH of the 1: 1 and 1: 2 [ligand: Co(II)] complexes were determined in KCl supporting electrolyte (p = 0. 100 M) at 25 degreesC. Dinuclear cobalt(H) complex could form a V-peroxo adduct at 1 atm oxygen atmosphere with the oxygenation constant log K-O2 = 3.19. The neutral homodinuclear complexes: [Co2C28H44N6O2(NO3)(2)](.)12H(2)O has been synthesized and its crystal structure has been reported with triclinic system, a = 8.3376(5), b = 9.4501(6), c = 14.1028(9) A, alpha = 73.9100(2), beta = 73.4940(2), gamma = 87.7310(2)degrees and Z = 1. Each cobalt(H) ion is complexed by half of the coordination sites of the dinucleating macrocycle, and the anionic nitrate enters into the coordination sphere and completes a six-coordinated octahedron. (C) 2002 Elsevier Science B.V. All rights reserved.