Copper(II) acetate-induced hydrolytic C–N bond cleavage of a topologically constrained tetraaza macrotricycle

A topologically constrained tetraaza macrotricycle, 2,2,4,10,10,12-hexamethyl-1,5,9,13-tetraazatricyclo[11.3.2.25.9]eicosane (L2), has been prepared by the reaction of 5,7,7,12,14,14-hexaazamethyl-1,4,8,11-tetraazacyclotetradecane (L1) with 1,3-dibromopropane. Interestingly, L2 reacts with Cu(OAc)2 · H2O to produce [CuL3]2+ (L3 = 2,2,4,10,10,12-hexamethyl-1,5,9,13-tetraazabicyclo[11.3.2]octadecane) as the only product under mild conditions, showing that the C–N bonds at one of the two N–CH2CH2–N linkages of the macrotricycle are readily broken in the presence of the metal salt. The complex [CuL3]2+ exhibits stronger ligand field strength than other related copper(II) complexes with a 5-6-6-6 chelate ring sequence and is unusually inert against decomposition in acid solutions.