Synthesis of new structurally constrained tetraaza macropolycyclic compounds containing two rigid bridges: Crystal structure and chemical properties of a copper(II) complex

New topologically constrained tetraaza macropolycycles L9, L10, and L11 containing two o-xylylene (–(CH2)C6H4(CH2)–) bridges have been prepared by the reaction of 1,2-bis(bromomethyl)benzene with 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane (L1), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L2), or 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L3). The macropolycycle L9 readily reacts with Cu2+ ion to form [CuL9]2+ in wet methanol. However, L10 and L11 do not bind the metal ion in similar conditions. The Cu–N distances [2.048(4)–2.070(4)] and the ligand field strength of [CuL9](ClO4)2 are considerably longer and weaker, respectively, than those of other related macropolycyclic copper(II) complexes containing two N-(CH2)2-N or N-(CH2)3-N bridges. The copper(II) complex is extremely stable even in low pH and quite inert against ligand substitution with CN− ion.