Oxidation of an o-iminobenzosemiquinone radical ligand by molecular bromine: structural, spectroscopic, and reactivity studies of a copper(II) o-iminobenzoquinone complex.
The bis(o-iminobenzosemiquinonato)copper(II) complex 1, containing the radical form [L(*)SQ](1-) arising from the aerial oxidation of the noninnocent ligand 2-anilino-4,6-di- tert-butylphenol, H2L, is readily oxidized by molecular bromine to a bis(o-iminobenzoquinone)copper(II) complex, 2. Thus, a ligand-based oxidative addition is reported for complex 1 containing an electron-rich Cu(II) d(9) metal ion. The crystal structure of the synthesized hexacoordinated complex [Cu(II)(LBQ)2Br2] (2) has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements and an X-band electron paramagnetic resonance spectrum establish the spin state to be St = 1/2 because of localized spin moments mainly in the (d(x(2)-y(2)))(1) orbital of a Cu(II) d(9) ion, indicating clearly the presence of a neutral iminobenzoquinone form, [LBQ](0), of the ligand in 2, as is found also in the X-ray structure. Electrochemical measurements (cyclic voltammograms and coulometry) indicate two successive one-electron reductions of the ligand. The reactivity of complex 2 as an oxidizing agent toward ethanol and triethylamine has been investigated.
Mukherjee
Chandan
C
Max-Planck-Institute for Bioinorganic Chemistry, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
Weyhermüller
Thomas
T
Bothe
Eberhard
E
Chaudhuri
Phalguni
P
D000438:Alcohols / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D016227:Benzoquinones / Q000737:chemistry*; D001966:Bromine / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D013053:Spectrophotometry
D000438:Alcohols; D000588:Amines; D016227:Benzoquinones; D005609:Free Radicals; D007097:Imines; D008024:Ligands; D009942:Organometallic Compounds; D003300:Copper; D001966:Bromine