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 Pequation image with a=11.4037(11), b=11.8184(12), c=14.6835(14) Å, Z=4 and those of 12 are triclinic, space group P1̅ with a=11.2692(9), b=12.8612(11), c=15.2439(12) Å 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 NiII and CoII. Reaction of NiCl₂·6H₂O with one molar equivalent of 11 in refluxing methanol followed by addition of NH₄PF₆ affords NiII complex 14. The assignment of an octahedral geometry to 14 follows from its paramagnetism (μ_eff=2.50 μ_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 P6₁, a=17.0747(16), b=17.0747(16), c=29.958(4) Å, Z=6. Co^II complexes 15 and 16 of selenaaza macrocycles were prepared by the reaction of Co(ClO₄)₂·6H₂O with 11 and 3, respectively. Complex 16: monoclinic, space group C₂, a=17.160(2), b=10.9660(14), c=9.4941(12) Å, Z=2. The cyclic voltammograms of 15 and 16 in MeCN solution show well-behaved quasi-reversible couples.