Takaharu OOKUBO (Kanazawa Univ.), Hideki SUGIMOTO, Toshihiko NAGAYAMA (Kanazawa Univ.), Hideki MASUDA (Nagoya Inst. Tech.), Takahisa SATO, Koji TANAKA, Yonezo MAEDA, Hisashi OKAWA (Kyushu Univ.), Yoshihito HAYASHI, Akira UEHARA (Kanazawa Univ.) and Masatatsu SUZUKI (Kanazawa Univ.)
[J. Am. Chem. Soc. 118, 701 (1996)]
The reaction of 2 equiv of Fe(BF4)2·6H20 with 1 equiv of HPh-bimp and C6H5COONa in EtOH under N2 gave [Fe2(Ph-bimp)(C6H5COO)](BF4)2·3H2O (2). Two iron centers in 2 are coordinatively unsaturated and readily react with O2 in acetonitrile to generate an oxygenated complex {Fe2(Ph-bimp)(C6H5COO)(O2)](BF4)2·CH3CN·C2H5OC2H5·H2O (1). The electronic spectrum of 2 in acetonitrile displays two d-d bands at 853 nm ((epsilon) = 12 dm3mol-1cm-1) and 1900 nm ((epsilon) = 22 dm3mol-1cm-1), typical of high-spin five coordinate Iron(II) centers. The complex 1 has an intense dark green color, its electronic spectrum in CH3CN at 20 °C showing a broad absorption band at 800-500 nm ((epsilon) = ca. 1700 dm3mol-1cm-1). Boiling the CH3CN solution of 1 under N2 resulted in decolorization of the solution. Bubbling of O2 through the solution restored the original dark green color. Thus, complex 1 is substantially thermally stable toward irreversible oxidation compared to the p-peroxo complexes reported so far. A single crystal suitable for X-ray crystallography was obtained by a diffusion of diethyl ether into an acetonitrile solution of 2 under O2 at -20 °C. The molecular structure of the dinuclear cation of 1 has a triply bridged structure with cis-1,2-peroxide, (mu)-Phenolate of Ph-bimp, and p-benzoate, which is quite similar to that of a (mu)-phenolate dicobalt complex. [Co2(bpmp)(C6H5COO)(O2)](BF4)2·H2O (3) Such a cis-(mu)-1,2-peroxo coordination mode has been suggested for [Fe2(N-Et-HPTB)(C6H5COO)-(O2)]2+. The equilibrium constant (K) of eq 1 for the oxygenation of 2 was measured by spectrophotometric titration in CH3CN at 20 °C under various partial pressures. K[P(O2)1/2 = 1/K] of 2 was estimated to be ca. 0.5 Torr-1.