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

Abstract New topologically constrained tetraaza macropolycycles L 9 , L 10 , and L 11 containing two o -xylylene (–(CH 2 )C 6 H 4 (CH 2 )–) bridges have been prepared by the reaction of 1,2-bis(bromomethyl)benzene with 3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.0 7.12 ]docosane (L 1 ), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (L 2 ), or 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L 3 ). The macropolycycle L 9 readily reacts with Cu 2+ ion to form [CuL 9 ] 2+ in wet methanol. However, L 10 and L 11 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 [CuL 9 ](ClO 4 ) 2 are considerably longer and weaker, respectively, than those of other related macropolycyclic copper(II) complexes containing two N -(CH 2 ) 2 - N or N -(CH 2 ) 3 - N bridges. The copper(II) complex is extremely stable even in low pH and quite inert against ligand substitution with CN − ion.