Metal Complexes with Macrocyclic Ligands. XIV. Formation, dissociation and metal exchange with an N 2 S 2 ‐macrocycle

10, 10, 12‐Trimethyl‐3,4‐benzo‐1,6‐dithia‐9,13‐diazacyclopentadecen‐dihydrochloride (LH   2 2+ , 2 ) and its Ni 2+ complex were synthesized and their reactivity studied. The formation kinetics of 2 with Cu 2+ were found to be a second order reaction between Cu 2+ or CuACO + and the monoprotonated form of the ligand LH + . The rate constant k   Cu LH= 29 M −1 S −1 is 10 5 –10 6 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 Cu 2+ and the ammonium group. The metal‐metal exchange between NiL + and Cu 2+ was also investigated. The reaction is independent of [Cu 2+ ] and has the same rate and activation parameters as the dissociation of NiL 2+ . In contrast to open chain ligands, no mixed complex CuNiL 4+ as intermediate was observed.