Oxidation of bis(μ-halo)-bis[(diamine)copper(I)] complexes [LCuX]2; L = TMED, X = Cl, Br or I, L = TEED or TMPD, X = Cl, with the two electron organo oxidizing agent, tetrachloro-l,2-benzoquinone(TClBQ) in aprotic media: models for intermediates in catalytic catechol oxidase

摘要

Well structurally characterized bis(μ-halo)-bis[(diamine)copper(I)] complexes [LCuX]2; L = TMED, tetramethyl-ethylenediamine, X = Cl, Br or I and L = TEED, tetraethylethylenediamine, or TMPD, tetramethylpropane-diamine, X = Cl, react quantitatively with tetrachloro-l,2-benzoquinone (TC1BQ) as two electron oxidizing agent in O2-free CH2Cl2 or PhNO2 to form a dimeric [LCuX]2Cat (Cat = catechol) as indicated by cryoscopic measurements. Infrared spectra was in agreement with total reduction of TClBQ to the corresponding catechol. Electronic spectra indicated a dimeric distorted five coordinate Cu(II) and EPR spectra suggested a square pyramidal arrangement around the Cu(II) centers in [LCuX]2Cat. The ligand field strength for diamine ligand was higher for the five member chelating ring (TMED) relative to the six membered one (TMPD). Electrochemical reduction of Cu centers in [LCuX]2Cat were irreversible and occurred at a less negative potential when X = I.