Metal Complexes with Macrocyclic Ligands. XIV. Formation,dissociation and metal exchange with an N2S2-macrocycle

10, 10, 12-Trimethyl-3,4-benzo-1,6-dithia-9,13-diazacyclopentadecen-dihydrochloride (LH, 2 ) and its Ni²⁺ complex were synthesized and their reactivity studied. The formation kinetics of 2 with Cu²⁺ were found to be a second order reaction between Cu²⁺ or CuACO⁺ and the monoprotonated form of the ligand LH⁺. The rate constant k = 29 M ^?1S ^?1 is 10⁵–10⁶ times smaller than those of monoprotonated tetraazamacrocycles either because of second bond formation or because of a strong electrostatic interaction between the positive charges of the Cu²⁺ and the ammonium group. The metal-metal exchange between NiL⁺ and Cu²⁺ was also investigated. The reaction is independent of Cu²⁺] and has the same rate and activation parameters as the dissociation of NiL²⁺. In contrast to open chain ligands, no mixed complex CuNiL⁴⁺ as intermediate was observed.