Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India.
Inorg Chem. 2011 Nov 21;50(22):11375-83. doi: 10.1021/ic200979q. Epub 2011 Oct 21.
The mononuclear copper(II) complex Cu(H(2)L(1))(2)(H(2)O)(2) (1) (where H(2)L(1) = 1,10-phenanthroline-5,6-dioxime) reacts with copper(II) perchlorate in acetonitrile at ambient conditions in the presence of triethylamine to afford a copper(II) complex, Cu(L(3))(2)(H(2)O)(2) (2a), of 1,10-phenanthroline furoxan. A similar complex Cu(L(3))(2)Cl (2) is isolated from the reaction of H(2)L(1) with copper(II) chloride, triethylamine, and sodium perchlorate in acetonitrile. The two-electron oxidation of the vic-dioxime to furoxan is confirmed from the X-ray single crystal structure of 2. An intermediate species, showing an absorption band at 608 nm, is observed at -20 °C during the conversion of 1 to 2a. A similar blue intermediate is formed during the reaction of [Cu(HDMG)(2)] (H(2)DMG = dimethylglyoxime) with ceric ammonium nitrate, but H(2)DMG treated with ceric ammonium nitrate does not form any intermediate. This suggests the involvement of a copper(II) complex in the intermediate step. The intermediate species is also observed during the two-electron oxidation of other vic-dioximes. On the basis of the spectroscopic evidence and the nature of the final products, the intermediate is proposed to be a mononuclear copper(II) complex ligated by a vic-dioxime and a dinitrosoalkene. The dinitrosoalkene is generated upon two-electron oxidation of the dioxime. The transient blue color of the dioxime-copper(II)-dinitrosoalkene complex may be attributed to the ligand-to-ligand charge transfer transition. The intermediate species slowly decays to the corresponding two-electron oxidized form of vic-dioxime, i.e. furoxan and Cu(CH(3)CN)(4). The formation of two isomeric furoxans derived from the reaction of an asymmetric vic-dioxime, hexane-2,3-dioxime, and copper(II) perchlorate supports the involvement of a dinitrosoalkene species in the intermediate step. In addition, the oxidation of 2,9-dimethyl-1,10-phenanthroline-5,6-dioxime (H(2)L(2)) to the corresponding furoxan and subsequent formation of a copper(I) complex Cu(L(4))(2) (3) (where L(4) = 2,9-dimethyl-1,10-phenanthroline furoxan) are discussed.
单核铜（II）配合物 Cu(H(2)L(1))(2)(H(2)O)(2) (1)（其中 H(2)L(1) = 1,10-菲咯啉-5,6-二肟）在乙腈中，在三乙胺存在下，于环境条件下与高氯酸铜反应，生成 1,10-菲咯啉呋喃叉的铜（II）配合物 Cu(L(3))(2)(H(2)O)(2) (2a)。类似的配合物 Cu(L(3))(2)Cl (2) 是由 H(2)L(1)与高氯酸铜、三乙胺和高氯酸钠在乙腈中的反应分离得到的。2 的 X 射线单晶结构证实了偕二肟向呋喃叉的两电子氧化。在 1 转化为 2a 的过程中，在-20°C 下观察到一种中间体，其在 608nm 处显示出吸收带。在 [Cu(HDMG)(2)]（H(2)DMG = 二甲基乙二肟）与硝酸铈铵的反应中也形成了类似的蓝色中间体，但用硝酸铈铵处理 H(2)DMG 不会形成任何中间体。这表明在中间体步骤中涉及到铜（II）配合物。在其他偕二肟的两电子氧化过程中也观察到中间体。基于光谱证据和最终产物的性质，提出该中间体是由偕二肟和二亚硝基亚烯配体配位的单核铜（II）配合物。二亚硝基亚烯是偕二肟二电子氧化生成的。偕二肟-铜（II）-二亚硝基亚烯配合物的瞬态蓝色可能归因于配体到配体的电荷转移跃迁。该中间体缓慢衰减为相应的偕二肟两电子氧化形式，即呋喃叉和 Cu(CH(3)CN)(4)。反应不对称偕二肟、己烷-2,3-二肟和高氯酸铜生成两种异构体呋喃叉，支持二亚硝基亚烯物种在中间体步骤中的参与。此外，讨论了 2,9-二甲基-1,10-菲咯啉-5,6-二肟（H(2)L(2)）氧化为相应的呋喃叉以及随后形成铜（I）配合物Cu(L(4))(2) (3)（其中 L(4) = 2,9-二甲基-1,10-菲咯啉呋喃叉）的过程。
