Mononuclear and dinuclear cobalt complexes and its dioxygen adduct with a new 24-membered hexaaza macrocyclic ligand

Dinucleating 24-membered hexaazadiphenol macrocyclic ligand 3,6,9,17,20,23- hexaaza-29,30-dihydroxy-13,27-dimethyl-tricyclo[23,3,1,1(11,15)] triaconta- 1(29), 11,13,15(30),25,27-hexaene (L or BDBPH), is prepared by the NaBH4 re duction of the Schiff base obtained from [2+2] template condensation of 2,6 -diformyl-p-cresol with diethylenetriamine. The ligand maintains dinuclear integrity for cobalt (II) while facilitating the formation of bridging phen olate dicobalt cores. Potentiometric equilibrium studies indicate that a va riety of protonated, mononuclear and dinuclear cobalt (11) complexes form f rom p[H] 2 through 11 in aqueous solution. The protonation constants of thi s ligand and stability constants of the 1: 1, 1: 2 ligand: cobalt(II) compl exes were determined in KCI supporting electrolyte (mu = 0.100 M) at 25 deg reesC. The mechanism for the formation of dinuclear dioxygen cobalt(II) com plexes is also described. The stability constants of mononuclear and dinucl ear cobalt complexes were determined under nitrogen. Preliminary results sh ow that the dinuclear dioxygen cobalt (11) complexes do not catalyze hydrox ylation of adamantane in the presence of H2S as two-electron reductant.