SYNTHESIS, PROPERTIES, AND COMPLEXATION OF A NEW IMIDAZOLE-PENDANT MACROCYCLIC 12-MEMBERED TRIAMINE LIGAND

A new 12-membered macrocyclic triamine with an imidazole-pendant group, 2-(4-imidazoyl)-1,5,9-triazacyclododecane (5), has been synthesized to study its complexation behavior with Zn(II) and Cu(II), along with the ease with which the metal-bound imidazolate anion is generated. The Zn(II) complex (6a) shows a close equatorial coordination of the imidazole (2.025 angstrom) in a distorted trigonal-bipyramidal structure with an additional chloride ion. Final R and R(w) were 0.030 and 0.040, respectively: C12H23N5-ZnCl(ClO4), orthorhombic, space group Pna2(1), with a = 14.574 (1) angstrom, b = 9.079 (1) angstrom, c = 13.506 (1) angstrom, rho-c = 1.627 (g cm-3) for Z = 4, V = 1787.0 (3) angstrom 3. The proton dissociation most likely from the Zn(II)- and Cu(II)-coordinated imidazole (6,7) occurs with pK(a) values of 10.3 and 9.3, respectively, at 25-degrees-C and I = 0.1 (KNO3). Mixtures of the Cu(II) (or Zn(II)) complex 6 and Cu(II) (or Zn(II)) [12]aneN3 ([12]aneN3 = 1,5,9-triazacyclododecane) complex 1 in alkaline CH3OH solution yield Cu(II),Cu(II) (or Zn(II),Zn(II)) dinuclear complexes bridged by the imidazolate anion, 8. A boron complex (9) has been isolated during the diborane reduction of the monooxo precursor 11.