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 L-9, L-10, and L-11 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[16.4.0.0(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 Cu2+ ion to form [CuL9](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 [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. (C) 2013 Elsevier B.V. All rights reserved.