作者:Greig Scott、Amelia McAnaw、David McKay、Alan S. F. Boyd、David Ellis、Georgina M. Rosair、Stuart A. Macgregor、Alan J. Welch、Franco Laschi、Fulvio Rossi、Piero Zanello
DOI:10.1039/c003067h
日期:——
13-vertex indenyl cobaltacarboranes with 4,1,6-, 4,1,10- and 4,1,2-CoC2B10 architectures have been synthesised by reduction of the corresponding closo carborane and metallation with an (η-C9H7)Co} fragment. Variants of the 4,1,6-isomer were prepared with no, one and two methyl groups on cage C atoms, whilst 4,1,2-species were obtained both with two methyl groups and a trimethylene tether on the cage C atoms. Thermolysis of the 4,1,6-isomers yielded the corresponding 4,1,8-isomers, which in turn were converted to 4,1,12-isomers by thermolysis at higher temperatures. Alternatively relatively mild heating of the 4,1,10-isomer led to the 4,1,12-isomer directly. Products were characterised by mass spectrometry, 1H and 11B NMR spectroscopies and, in most cases, elemental analysis, and nine compounds were studied crystallographically. The 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- species have docosahedral cages whilst the 4,1,2-species are henicosahedral. In the structural studies attention focused on the orientation of the indenyl ligand with respect to the carborane ligand since this affords experimental information on the metal-cage bonding through the structural indenyl effect. There is a general tendency for the indenyl ligand to adopt orientations in which the ring junction C atoms lie trans to cage B atoms. In cases where the orientation is not compromised by the presence of a non-H substituent on the face of the carborane there is generally good agreement between the experimental orientation and that computed by DFT calculations for the related naphthalene ferracarboranes (η-C10H8)FeC2B10H12. The presence of C-methyl substituents in the indenyl cobaltacarboranes tends to override this preference except in the case of 1,6-Me2-4-(η-C9H7)-4,1,6-closo-CoC2B10H10 where the indenyl ligand instead is forced to incline away from the cage methyl groups. In DCM solution the 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- isomers of (η-C9H7)CoC2B10H12 exhibit two, stepwise, 1-electron reductions assigned to Co(III)/Co(II)/Co(I) couples at less negative potentials than those of the corresponding Cp compounds. Moreover these reductions are easier for those isomers (4,1,6- and 4,1,10-) in which there are two cage C atoms in the carborane face to which the metal atom is bound. By spectroelectrochemical and EPR measurements it is concluded that the reductions of these indenyl cobaltacarboranes are largely metal-based.
通过还原相应的闭碳
硼烷并用(η-
C9H7)Co}片段
金属化,合成了具有 4,1,6-、4,1,10-和 4,1,2-CoC2B10结构的 13 芯
茚基
钴硼烷。制备出的 4,1,6-异构体笼 C 原子上没有、有一个和两个甲基,而 4,1,2-异构体笼 C 原子上有两个甲基和一个三亚甲基。4,1,6-异构体的热分解产生了相应的 4,1,8-异构体,这些异构体又在较高温度下通过热分解转化为 4,1,12-异构体。另外,对 4,1,10-异构体进行相对温和的加热,可直接生成 4,1,12-异构体。通过质谱、1H 和 11B NMR 光谱以及大多数情况下的元素分析对产品进行了表征,并对九种化合物进行了晶体学研究。4,1,6-、4,1,8-、4,1,10- 和 4,1,12- 种类具有二十二面笼型,而 4,1,2 种类则为七面笼型。结构研究的重点是
茚基
配体相对于碳
硼烷配体的取向,因为这可以通过
茚基结构效应提供有关
金属笼键合的实验信息。
茚基
配体一般倾向于采用环结点 C 原子反向位于笼 B 原子的取向。在碳
硼烷表面存在非 H 取代基而不影响取向的情况下,实验取向与通过 DFT 计算得出的相关
萘铁碳
硼烷 (η-
C10H8)FeC2B10H12 的取向基本吻合。除了 1,6-Me2-4-(η- )-4,1,6-closo-CoC2B10H10 的情况外,
茚基
钴硼烷中 C-甲基取代基的存在往往会推翻这种偏好,在这种情况下,
茚基
配体被迫向远离笼状甲基的方向倾斜。在
二氯甲烷溶液中,(η- )CoC2B10H12 的 4,1,6-、4,1,8-、4,1,10- 和 4,1,12-异构体在负电位低于相应 Cp 化合物的负电位时,表现出两种逐步的 1 电子还原反应,这些还原反应归因于 Co(III)/Co(II)/Co(I) 偶联。此外,对于
金属原子结合的碳
硼烷面上有两个笼状 C 原子的异构体(4,1,6- 和 4,1,10-)来说,这些还原更容易。通过光谱电
化学和 EPR 测量得出的结论是,这些
茚基
钴硼烷的还原主要是以
金属为基础的。