COMPARATIVE BONDING PROPERTIES OF SEMIQUINONATE AND IMINOSEMIQUINONATE RADICAL LIGANDS IN RN(CO)(2)(3,6-DBSQ)(2) AND RU(CO)(2)(PHENOXSQ)(2)

Semiquinonate and iminosemiquiononate complexes of ruthenium have been prepared by treating Ru-3(CO)(12) with 3,6-di-tert-butyl-1,2-benzoquinone (3,6-DBBQ) and 2,4,6, 8-tetra-tert-butylphenoxazin-1-one (PhenoxBQ). Crystallorgraphic characterization of Ru(CO)(2)(3,6-DBSQ)(2) obtained as the 2-propanol solvate (tetragonal, P (4) over bar 2(1)c, a = 19.066(2) Angstrom, c = 18.420(5) Angstrom, V = 6696(2) Angstrom(3), Z = 8, R = 0.041) has shown that the carbonyl ligands are coordinated at cis sites. Structural characterization of Ru(CO)(2)(PhenoxSQ)(2) carried out on crystals obtained as the dichloromethane solvate (orthorhombic, Pbca, a = 31.215(6) Angstrom, b = 12.393(3)Angstrom, c = 30.664(6)Angstrom, V = 11862(5)Angstrom(3), Z = 8, R = 0.069) has shown that the carbonyl ligands bond at cis sites that are trans to the iminosemiquinone oxygen atoms. Radical ligands are antiferromagnetically coupled, resulting in diamagnetism and sharp NMR spectra for both complex molecules. Five-membered redox series consisting of two oxidations and two reductions, all ligand-based, appear in the electrochemistry. Potentials of iminoquinone couples are shifted negatively by approximately 0.5 V relative to corresponding quinone redox steps.