研究室工作進展 Apr. 13th, 2017
Spiro Metalla-aromatics of Pd, Pt, Rh: Synthesis and Characterization
Yongliang Zhang, Junnian Wei, Yue Chi, Xuan Zhang, Wen-Xiong Zhang,* and Zhenfeng Xi*
J. Am. Chem. Soc. 2017, 139, 5039-5042.
Spiro metalla-aromatics, a new aromatic system, has been realized for the first time in this work. The synthesis and characterization of spiro metallaaromatics of Pd, Pt, and Rh, in which the transition metal (Pd, Pt, or Rh) is the spiro atom, that cross-conjugates two aromatic five-membered metallacycles, are described. These spiro metallaaromatics tend to take square planar geometries, with the dihedral angle being influenced by the steric repulsion between the α-positioned substituents. All these results are rationalized and classified via both experimental measurements (X-ray structural analysis, NMR spectroscopy, XPS, etc.) and theoretical analysis (DFT calculation, ISE, AICD, NICS, and CMOs).
Since the concept of aromaticity represents one of the most fundamental and important principles in chemistry, the search for unprecedented and exciting aromatic systems, therefore, continues to drive research in this area. This work, by filling the void of spiro skeletons and aromaticity theory, shall lead to a novel field of organometallic chemistry and aromatic systems.
亮點介紹
Making the Impossible Possible
芳香性是化學學科中最基礎最重要的概念之一，而芳香性體系在化學及材料科學中發揮着重要作用。因此，發現新的芳香體系具有重要意義。
螺環化合物[碳為螺原子]是有機化學中常見的環狀化合物。碳原子的成鍵本質決定了有機螺環化合物不可能具有芳香性。但是，如果把碳螺原子換成過渡金屬，則構成金屬雜螺環化合物[金屬離子為螺原子]。由于金屬的軌道特性，金屬雜螺芳香性化合物就成為可能。本研究室已經發現雙锂試劑的共轭丁二烯骨架能夠同兩個碳負離子産生“協同效應”，使其LUMO軌道能級相對于1,3-丁二烯顯著降低，從而可以接受合适的過渡金屬的d電子并離域至其π*軌道(魏俊年等，Angew. Chem. Int. Ed. 2015, 54, 5999; 2015, 54, 9986; J. Am. Chem. Soc. 2016, 138, 60.)。在該項工作中張永亮等同學利用雙锂試劑的這一獨特性質并結合過渡金屬配位化學，首次成功構建了金屬雜螺芳香化合物“Making the Impossible Possible”。