Preparation, properties, and crystal structure of a novel series of macrocyclic organocobalt complexes

Article abstract of DOI:10.1021/ic00273a015

The organocobalt complexes [(H₂O)([14]aneN₄)CoR](ClO₄)₂ (R = primary alkyl, substituted primary alkyl, and benzyl; [14]aneN₄ = 1,4,8,11-tetraazacyclotetradecane) were prepared photochemically from the corresponding alkylcobaloximes and the cobalt(II) macrocycle. The complexes were characterized by elemental analysis, ¹H NMR spectroscopy, a crystal structure determination for R = ethyl, and UV-visible spectroscopy. The ethyl complex, [(H₂O)([14]aneN₄)CoC₂H₅](ClO ₄)₂·H₂O, crystallizes in the monoclinic crystal system, space group P2₁/n, with four molecules in a unit cell of dimensions a = 8.901 (11) A, b = 12.254 (21) A, c = 19.637 (15) A, and β = 91.76 (22)°. The data refined to a final value of the weighted R factor of 0.083 based on 1242 independent observations. The complex is hexacoordinated, with the ethyl group and a coordinated molecule of water as axial ligands. All of the complexes are photosensitive and readily decompose to cobalt(II) and carbon-centered radicals when irradiated with visible light. Air-stable acidic aqueous solutions of the alkyl complexes show no sign of decomposition in hours when kept in the dark. The hydroxymethyl complex, prepared by a modified Fenton reaction, is air-sensitive, and the benzyl complex undergoes rapid homolysis of the cobalt-carbon bond.