Synthesis and characterization of some new 22-membered chalcogenoaza macrocycles and their Co-II and Ni-II complexes

Abstract

The [2+2] cyclocondensation of bis(o-formylphenyl)chalcogenides (9, 10) with trans-1,2-diaminocyclohexane affords novel macrocyclic ligands 11 and 12 in very good yields. Crystals of 11 are triclinic, space group P (1) over bar with a = 11.4037(11), b = 11.8184(12), c = 14.6835(14) angstrom, Z = 4 and those of 12 are triclinic, space group P (1) over bar with a = 11.2692(9), b = 12.8612(11), c = 15.2439(12) angstrom and Z = 2. Reduction of 11 with sodium borohydride affords macrocycle 13. The coordination chemistry of 11 has been studied with the "hard" metal ions Ni-II and Co-II. Reaction of NiCl2 center dot 6H(2)O with one molar equivalent of 11 in refluxing methanol followed by addition of NH4PF6 affords Ni-II complex 14. The assignment of an octahedral geometry to 14 follows from its paramagnetism (mu(eff) = 2.50 mu(B)) and UV/Vis spectrum and was further confirmed by single-crystal X-ray diffraction studies. The crystal structure of 14 consists of a distorted octahedral nickel center coordinated by two selenium and four nitrogen atoms. Complex 14: hexagonal, space group P6(1), a = 17.0747(16), b = 17.0747(16), c = 29.958(4) angstrom, Z = 6. Co-II complexes 15 and 16 of selenaaza macrocycles were prepared by the reaction of Co(ClO4)(2)center dot 6H(2)O with 11 and 3, respectively. Complex 16: monoclinic, space group C-2, a = 17.160(2), b = 10.9660(14), c = 9.4941(12) angstrom, Z = 2. The cyclic voltammograms of 15 and 16 in MeCN solution show well-behaved quasi-reversible couples.