Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes
作者:Lothar Weber、Jan Kahlert、Lena Böhling、Andreas Brockhinke、Hans-Georg Stammler、Beate Neumann、Rachel A. Harder、Paul J. Low、Mark A. Fox
DOI:10.1039/c2dt32378h
日期:——
Fifteen C-diazaborolyl-ortho-carboranes, 1-R′-2-R′′-1,2-C2B10H10, where R′ represents the groups 2-(1,3-Et2-1,3,2-N2BC6H4)-, 2-(1,3-Ph2-1,3,2-N2BC6H4)-, 2-(1,3-Ph2-5,6-Me2-1,3,2-N2BC6H2)-, 2-(1,3-iPr2-1,3,2-N2BC6H4)-, and 2-(1,3,2-N2BC6H6)- and where R′′ is H, Me, Ph, tBu or SiMe3, were synthesized. Cyclic voltammetry studies of the compounds showed irreversible oxidation waves which are caused by the oxidation of the heterocycle. Those C-diazaborolyl-ortho-carboranes with Ph, tBu and SiMe3 substituents at the adjacent C-atom of the cage displayed two one-electron reduction waves reflecting the formation of stable radical monoanions with unusual (2n + 3) skeletal electron counts. The geometries of these anions were determined by combinations of infrared, UV-visible spectroelectrochemical and computational studies. Additionally the structures of seven new C-diazaborolyl-ortho-carboranes and one new 2-bromo-1,3,2-benzodiazaborole were determined by X-ray crystallography and compared with previously obtained structures.
合成了十五种C-二氮硼烯-邻氮杂卡宾,1-R′-2-R′′-1,2-C2B10H10,其中R′代表的取代基为2-(1,3-Et2-1,3,2-N2BC6H4)-、2-(1,3-Ph2-1,3,2-N2BC6H4)-、2-(1,3-Ph2-5,6-Me2-1,3,2-N2BC6H2)-、2-(1,3-iPr2-1,3,2-N2BC6H4)-和2-(1,3,2-N2BC6H6)-,而R′′为H、Me、Ph、tBu或SiMe3。对这些化合物进行循环伏安法研究时发现其显示出不可逆的氧化波,这种现象是由杂环的氧化引起的。具有Ph、tBu和SiMe3取代基的C-二氮硼烯-邻氮杂卡宾在笼体相邻C原子上表现出两条单电子还原波,反映出形成了具有不寻常(2n + 3)骨架电子计数的稳定自由基单阴离子。这些阴离子的几何结构通过红外、紫外可见光光谱电化学和计算研究的结合得以确定。此外,七种新的C-二氮硼烯-邻氮杂卡宾和一种新的2-溴-1,3,2-苯二氮硼烯的结构通过X射线晶体学确定,并与之前获得的结构进行了比较。