Preparation, Structure, and Spectroscopy of Cobalt(III) Complexes Containing N,N-Di-8-quinolyl Derivatives of 1,2-Diaminoethane, (R)-1,2-Diaminopropane, and (R,R)-l, 2-Diaminocyclohexane

Mixed-ligand cobalt(III) complexes have been prepared by the reaction of tris(acetylacetonato)cobalt(III) with an N,-N′-N-8-quinolyl-l,2-diaminoalkane (1,2-diaminoethane, (R)-1,2-diaminopropane, and (R,R)-1,2-diaminocyclohexane) in organic solvents. The isolated complexes have deprotonated secondary amino nitrogens. The parent complexes with neutral ligands were readily formed on addition of hydrogen chloride in organic solvents, but the crystals were isolated with difficulty. The absorption, CD, and ¹H NMR spectra change rapidly and reversibly on protonation and deprotonation of the quadridentate ligand. The X-ray crystal structure analysis of [Co(acac)(R-dqpn)]ClO₄, which contains the deprotonated form of dqpn (dqpn = N,N′-di-8-quinolyl-l,2-diaminopropane), has been performed in order to clarify the detailed structure. Crystal data: CoClO₆N₄C₂₆H₂₆, a = 11.112 (2) Å, b = 13.299 (5) Å, c = 9.275 (4) Å, α = 106.06 (4), β = 88.72 (3), γ = 85.87 (3), space group P1,Z = 2, R = 5.7% for 4327 observed reflections. The two independent complex cations consist of the Δ- and Λ-isomers. The stereochemistry including geometrical and optical isomerism of both the protonated and deprotonated complexes is discussed on the basis of the crystal structure and spectroscopic data in solution. The quadridentate ligands seem to undergo rapid rearrangement on protonation and deprotonation of the complexes.