New-Dimensional Cyclam. Synthesis, Crystal Structure, and Chemical Properties of Macrocyclic Tetraamines Bearing a Phenol Pendant.

Newly devised 13-15-membered macrocyclic tetraamine (N4) ligands attached with a phenolic pendant (10, 11, 13, and 15) have been synthesized to determine the influence of the phenol on the cation-enclosure properties of the macrocyclic N4 and, conversely, the influence of the proximate cations encompassed in N4 macrocycles on the chemical behavior of the phenolate pendant. The synthesis involves a novel annelation reaction between coumarin and suitable tetraamines. The favorable location of phenol in the periphery of the macrocycle has been confirmed by the X-ray crystal structure of the phenol-pendant 14-membered N4 (cyclam) l l b . Dissociation of the phenolic protons is facilitated by incorporation of metal ions into the macrocycle, and the resulting phenolate ion atop stabilizes otherwise unstable complexes. The crystal structures of I l b and its Cu" complex 17a have been determined. The crystals of l l b (C16H28N40) are monoclinic, space group P2,/a, with four molecules in the unit cell of dimensions u = 15.335 (8) A, b = 8.535 (5) A, c = 13.331 (7) A, and 0 = 105.17 (5)'. Crystals of l7a(CIO4).H2O (C16H27N,0CuC104~H,0) are also monoclinic, space group P 2 , / n , with four molecules in the unit cell of dimensions a = 30.943 ( 2 0 ) A, b = 8.188 (4) A, c = 7.936 (4) A, and /3 = 95.89 (5)O. The structures were solved by the direct method for l l b and the heavy-atom method for 17a and refined by block-diagonal least-squares calculations: for I lb , R = 0.061 for 2635 independent reflections, and for 17a, R = 0.066 for 3703 independent reflections. The five-coordinate, square-pyramidal geometry around copper is illustrated with the phenolate oxygen at nearly the apex of the pyramid. The pH-metric and polarographic titration of Cu"-llb revealed a complexation constant ([CuH_,L+]/[Cul'][H-,L-]) of 1.0 X M-I (H_,L is the phenolate species) and stability enhancement of I O 2 by the phenolate coordination. Its strong u donation contributes to stabilization of higher oxidation states of metal ions.