Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan.
Inorg Chem. 2010 Nov 15;49(22):10264-72. doi: 10.1021/ic9018794. Epub 2010 Oct 14.
Self-assembled, chair-shaped dirhenium(I) macrocyclic compounds featuring the two different bis-chelating quinone dianions (1, L = dhnq(2-); 2, L = dhaq(2-); H(2)dhnq = 6,11-dihydroxy-5,12-naphthacenedione; H(2)dhaq = 1,4-dihydroxy-9,10-anthraquinone) that interface with two fac-Re(CO)(3) cores and a ditopic semirigid N-donor 1,4-bis(5,6-dimethylbenzimidazol-1-ylmethyl)naphthalene (L' = p-NBimM) ligand coordinated to the remaining orthogonal site were prepared in high yields. Their structures were confirmed by single-crystal X-ray diffraction analysis. Electrochemical assessments, using cyclic voltammetry (CV) and UV-vis-NIR spectroelectrochemistry (SEC), revealed the existence of two well-separated, single-electron quinone ligand-centered, reversibly accessible 0, -1, and -2 redox states. Among the two singly reduced radical complexes, the symmetrically bridged quinone complex 1(•-), showed a strong absorption in the NIR regions, which was not observed for the neutral and doubly reduced states, analogous to that of the free dhnq(3•-) quinone. In contrast, when 2 was reduced to 2(•-), a broad signal at 866 nm was observed, very similar to the reduced dhaq(3•-) quinone. This difference in spectral behavior in the singly reduced states is likely due to the annealed benzene ring in 1 and dhnq(2-) because of its symmetrical π-electron system, which is perturbed to a lesser degree compared to asymmetric 2 and dhaq(2-). Reduction to 1(•-) produces a small but not negligible g factor anisotropy (Δg = 0.024) in the electron spin resonance (ESR) signal, indicative of a very small metal-centered spin (5%), but 2(•-) shows a g value in the expected range for organic radicals (no detectable Δg). Thus, the combined investigations reveal that the singly reduced metallacycles are best described as being highly stable, noncommunicating, localized, quinonoid-centered radical complexes, (CO)(3)Re(I)(μ-L(3•-))(μ-L')Re(I)(CO)(3).
自组装的椅型二铼（I）大环化合物具有两个不同的双螯合醌二阴离子（1，L = dhnq（2-）；2，L = dhaq（2-）；H（2）dhnq = 6,11-二羟基-5,12-萘二酮；H（2）dhaq = 1,4-二羟基-9,10-蒽醌），与两个 fac-Re（CO）（3）核和一个双位点半刚性 N-供体 1,4-双（5,6-二甲基苯并咪唑-1-基甲基）萘（L'= p-NBimM）配体配位到剩余的正交位点结合。它们的结构通过单晶 X 射线衍射分析得到证实。使用循环伏安法（CV）和紫外可见近红外光谱电化学（SEC）进行电化学评估表明，存在两个分离良好的、单电子醌配体中心、可还原的 0、-1 和-2 氧化还原态。在两个单还原自由基配合物中，对称桥联醌配合物 1(•-)在近红外区域显示出强烈的吸收，而中性和双还原态则没有观察到，类似于游离的 dhnq（3•-）醌。相比之下，当 2 还原为 2(•-)时，观察到 866nm 处的宽信号，与还原的 dhaq（3•-）醌非常相似。这种单还原态光谱行为的差异可能归因于 1 中退火的苯环和 dhnq（2-），因为其对称的π电子系统受到的干扰程度较小，与不对称的 2 和 dhaq（2-）相比。1(•-)的还原产生了电子自旋共振（ESR）信号中很小但不可忽略的 g 因子各向异性（Δg = 0.024），表明金属中心自旋很小（5%），但 2(•-)的 g 值在有机自由基的预期范围内（无可检测的Δg）。因此，综合研究表明，单还原的金属环最好被描述为高度稳定、不通信、局域、醌型中心自由基配合物，(CO)(3)Re(I)(μ-L(3•-))(μ-L')Re(I)(CO)(3)。
