Shimazaki Yuichi, Kabe Ryota, Huth Stefan, Tani Fumito, Naruta Yoshinori, Yamauchi Osamu
Institute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan.
Inorg Chem. 2007 Jul 23;46(15):6083-90. doi: 10.1021/ic700596g. Epub 2007 Jun 27.
Co(III) complexes of N(3)O-donor tripodal ligands, 2,4-di(tert-butyl)-6-{[bis(2-pyridyl)methyl]aminomethyl}phenolate (tbuL), 2,4-di(tert-butyl)-6-{[bis(6-methyl-2-pyridyl)methyl]aminomethyl}phenolate (tbuL(Mepy)(2)), were prepared, and precursor Co(II) complexes, [Co(tbuL)Cl] (1) and [Co(tbuL(Mepy)(2))Cl] (2), and ternary Co(III) complexes, [Co(tbuL)(acac)]ClO(4) (3), [Co(tbuL)(tbu-cat)] (4), and [Co(tbuL(Mepy)(2))(tbu-SQ)]ClO(4) (5), where acac, tbu-cat, and tbu-SQ refer to pentane-2,4-dionate, 3,5-di(tert-butyl)catecholate, and 3,5-di(tert-butyl)semiquinonate, respectively, were structurally characterized by the X-ray diffraction method. Complexes 3 and 5 have a mononuclear structure with a fac-N(3)O(3) donor set, while 4 has a mer-N(3)O(3) structure. The cyclic voltammogram (CV) of complex 3 exhibited one reversible redox wave centered at 0.93 V (vs Ag/AgCl) in CH(3)CN. Complex 5 was converted to a phenoxyl radical species upon oxidation with Ce(IV), showing a characteristic pi-pi* transition band at 412 nm. The ESR spectrum at low temperature and the resonance Raman spectrum of 3 established that the radical species has a Co(III)-phenoxyl radical bond. On the other hand, the CVs showed two oxidation processes at E(1/2) = 0.01 and E(pa) = 0.92 V for 4 and E(1/2a) = 0.05 and E(1/2b) = 0.69 V for 5. The rest potential of 4 (-0.11 V) was lower than the E(1/2) value, whereas that of 5 (0.18 V) was higher, indicating that the first redox wave of 4 and 5 is assigned to the tbu-cat and the tbu-SQ redox process, respectively. One-electron oxidized 4 showed absorption, resonance Raman, and ESR spectra which are similar to those of 5, suggesting formation of a stable Co(III)-semiquinonate species, which has the same oxidation level of 5. The resonance Raman spectrum of two-electron oxidized 4 showed the nu(8a) bands of the semiquinonate and phenoxyl radical, which were absent in the spectrum of one-electron oxidized 5. Since both oxidized species were ESR inactive at 5 K, the former was concluded to be a biradical species containing semiquinonate and phenoxyl radicals coupled antiferromagnetically and the latter to a species with a coordinated quinone.
制备了含N(3)O供体三脚架配体的Co(III)配合物，即2,4 - 二（叔丁基）-6-{[双（2 - 吡啶基）甲基]氨基甲基}酚盐（tbuL）、2,4 - 二（叔丁基）-6-{[双（6 - 甲基 - 2 - 吡啶基）甲基]氨基甲基}酚盐（tbuL(Mepy)(2)），以及前体Co(II)配合物[Co(tbuL)Cl] (1)和[Co(tbuL(Mepy)(2))Cl] (2)，还有三元Co(III)配合物[Co(tbuL)(acac)]ClO(4) (3)、[Co(tbuL)(tbu - cat)] (4)和[Co(tbuL(Mepy)(2))(tbu - SQ)]ClO(4) (5)，其中acac、tbu - cat和tbu - SQ分别指戊烷 - 2,4 - 二酮、3,5 - 二（叔丁基）邻苯二酚盐和3,5 - 二（叔丁基）半醌盐。通过X射线衍射法对这些配合物进行了结构表征。配合物3和5具有面式 - N(3)O(3)供体构型的单核结构，而4具有反式 - N(3)O(3)结构。配合物3在乙腈中的循环伏安图（CV）显示在0.93 V（相对于Ag/AgCl）处有一个可逆氧化还原波。用Ce(IV)氧化后，配合物5转变为酚氧基自由基物种，在412 nm处显示出特征性的π - π*跃迁带。低温下的电子顺磁共振（ESR）谱和配合物3的共振拉曼光谱表明该自由基物种具有Co(III) - 酚氧基自由基键。另一方面，CV显示配合物4在E(1/2) = 0.01和E(pa) = 0.92 V处有两个氧化过程，配合物5在E(1/2a) = 0.05和E(1/2b) = 0.69 V处有两个氧化过程。配合物4的静止电位（-0.11 V）低于E(1/2)值，而配合物5的静止电位（0.18 V）高于该值，这表明配合物4和5的第一个氧化还原波分别归因于tbu - cat和tbu - SQ的氧化还原过程。单电子氧化的配合物4显示出与配合物5相似的吸收、共振拉曼和ESR光谱，表明形成了具有与配合物5相同氧化态的稳定Co(III) - 半醌物种。双电子氧化的配合物4的共振拉曼光谱显示出半醌和酚氧基自由基的ν(8a)带，而单电子氧化的配合物5的光谱中没有这些带。由于两种氧化物种在5 K时均无ESR活性，因此得出前者是一种含有反铁磁耦合的半醌和酚氧基自由基的双自由基物种，后者是一种具有配位醌的物种。
