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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 14, Number 2
BKCSDE 14(2)
February 20, 1993 

Dioxygen Binding to Dirhodium(Ⅱ,Ⅱ), (Ⅱ,Ⅲ), and (Ⅲ,Ⅲ) Complexes. Spectroscopic Characterization of [Rh2(ap)4(O2)]+, Rh2(ap)4(O2), and [Rh2(ap)4(O2)]-, where ap = 2-anilinopyridinate Ion
Jae-Duck Lee*, Chao-Liang Yao, Francoise J. Capdevielle, Baocheng Han, John L. Bear, Karl M. Kadish
The neutral, reduced, and oxidized 2,2-trans isomers of Rh2(ap)4 (ap=2-anilinopyridinate) were investigated with respect to dioxygen binding in CH2Cl2 containing 0.1 M tetrabutyl-ammonium perchlorate. Rh2(ap)4 binds dioxygen in nonaqueous media and forms a RhⅡRhⅢ superoxide complex, Rh2(ap)4(O2). This neutral species was isolated and is characterized by UV-visible and IR spectroscopy, mass spectrometry and cyclic voltammetry. It can be reduced by one electron at E1/2 = -0.45 V vs. SCE in CH2Cl2 and gives [Rh2(ap)4(O2)]- as demonstrated by the ESR spectrum of a frozen solution taken after controlled potential reduction. The superoxide ion in [Rh2(ap)4(O2)]- is axially bound to one of the two rhodium ions, both of which are in a +2 oxidation state. Rh2(ap)4(O2) can also be stepwise oxidized in two one-electron transfer steps at E1/2 = 0.21 V and 0.85 V vs. SCE in CH2Cl2 and gives [Rh2(ap)4(O2)]+ followed by [Rh2(ap)4(O2)]2+. ESR spectra demonstrate that the singly oxidized complex is best described as [RhⅡ RhⅢ(ap)4(O2)]+ where the odd electron is delocalized on both of the two rhodium ions and the axial ligand is molecular oxygen.
195 - 200
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