研究室工作进展 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.
亮点介绍
Making the Impossible Possible
芳香性是化学学科中最基础最重要的概念之一，而芳香性体系在化学及材料科学中发挥着重要作用。因此，发现新的芳香体系具有重要意义。
螺环化合物[碳为螺原子]是有机化学中常见的环状化合物。碳原子的成键本质决定了有机螺环化合物不可能具有芳香性。但是，如果把碳螺原子换成过渡金属，则构成金属杂螺环化合物[金属离子为螺原子]。由于金属的轨道特性，金属杂螺芳香性化合物就成为可能。本研究室已经发现双锂试剂的共轭丁二烯骨架能够同两个碳负离子产生“协同效应”，使其LUMO轨道能级相对于1,3-丁二烯显著降低，从而可以接受合适的过渡金属的d电子并离域至其π*轨道(魏俊年等，Angew. Chem. Int. Ed. 2015, 54, 5999; 2015, 54, 9986; J. Am. Chem. Soc. 2016, 138, 60.)。在该项工作中张永亮等同学利用双锂试剂的这一独特性质并结合过渡金属配位化学，首次成功构建了金属杂螺芳香化合物“Making the Impossible Possible”。