Copper-Catechol Chemistry. Synthesis, Spectroscopy, and Structure of Bis(3,5-di-tert-butyl-o-semiquinato)copper(II)

Article abstract of DOI:10.1021/ja00268a031

The synthesis, spectroscopy, structure, and reactivity of bis(3,5-di-tert-butyl-o-semiquinato)copper(II), Cu(DTBSQ)2, a Cu(II)-semiquinone complex, are presented.This compound was prepared by reacting X (X = ClO4, Cl) with the corresponding benzoquinone or a basic Cu(II) dimer, (ClO4)2, with the catechol.The complex, which was characterized by analytical, spectroscopic, and X-ray diffraction techniques, crystallizes in the triclinic space group <*> with Z = 2 in a unit cell of dimensions a = 10.262 (3) Angstroem, b = 14.554(4) Angstroem, c = 9.418(2) Angstroem, α = 101.09(2) deg, β = 92.31(2) deg, γ = 108.87(2) deg at -100 deg C.Least-squares refinement of 298 variables led to a value of the conventional R index of 0.049 and R_w = 0.046 for 2296 reflections having I > 3?(I).Each copper ion is coordinated to four oxygen atoms from two DTBSQ ligands.In addition, there is a fifth oxygen atom from a neighboring Cu(DTBSQ)2 molecule coordinated to the copper atom in an axial position; thus, the overall geometry about the metal ion approaches square pyramidal.The C-O bond lengths of the DTBSQ ligands range from 1.290(7) to 1.296(6) Angstroem.The spectroscopic properties and reactions of Cu(DTBSQ)2 are consistent with the Cu(II)-semiquinone formulation.These results suggest that the copper oxidation of catechols takes place in two one-electron-transfer steps.