Mechanistic Insights into Ring Cleavage and Contraction of Benzene over a Titanium Hydride Cluster
Mechanistic Insights into Ring Cleavage and Contraction of Benzene over a Titanium Hydride Cluster
复制标题
DOI：
10.1021/jacs.6b03545
复制
发表时间：
2016-09-14
影响因子：
15
通讯作者：
Hou, Zhaomin
中科院分区：
文献类型：
--
作者：
Kang, Xiaohui;Luo, Gen;Hou, Zhaomin
过渡金属对苯的碳-碳键断裂具有重大的根本意义和实际重要性，因为这种转化涉及固体催化剂上石脑油工业加氢裂化中的文件和其他重要化学品的生产。尽管这种转变被认为依赖于多个金属位点的合作，但迄今为止有关反应机制的分子水平信息仍然很少。在这里，我们报告了分子三核氢化钛簇对苯的环裂解和收缩的 DFT 研究。我们的研究表明，该反应是由苯配位引发的，然后是H-2释放，C6H6加氢金属化，重复C-C和C-H键断裂和形成，得到MeC5H4单元，并将Ti原子插入MeC5H4单元中，释放H-2，得到金属环产物。甲苯的C-C键断裂和环收缩也可以以类似的方式发生，尽管由于甲基取代基的存在而导致一些细节有所不同。显然，H-2从金属氢化物簇中轻松释放以提供电子并改变金属中心的电荷数量，结合灵活的金属氢化物连接和三金属框架的动态氧化还原行为，使得这种不寻常的转变得以发生。这项工作不仅为苯在多金属框架上的活化和转化提供了前所未有的见解，而且还可能为设计用于非活性芳烃的活化和转化的新型分子催化剂提供帮助：
Carbon-carbon bond cleavage of benzene by transition metals is of great fundamental interest and practical importance, as this transformation is involved in the production-of file's and other important chemicals in the industrial hydrocracking of naphtha on solid catalysts. Although this transformation is thought to rely on cooperation of multiple metal sites, molecular-level information on the reaction mechanism has remained scarce to date. Here, we report the DFT studies of the ring cleavage and contraction, of benzene by a molecular trinuclear titanium hydride cluster. Our studies suggest that the reaction is initiated by benzene coordination, followed by H-2 release, C6H6 hydrometalation, repeated C-C and C-H bond cleavage and formation to give a MeC5H4, unit, and insertion of a Ti atom into the MeC5H4 unit with release of H-2 to give a metallacycle product. The C-C bond cleavage and ring contraction of toluene can also occur in a similar fashion, though some details are different due to the presence of the methyl substituent. Obviously, the facile release of H-2 from the metal hydride cluster to provide electrons and to alter the charge population at the metal centers, in combination with the flexible metal-hydride connections and dynamic redox behavior of the trimetallic framework, has enabled this unusual transformation to occur. This work has not only provided :unprecedented insights into the activation and transformation of benzene over a multimetallic framework but it may also offer help in the design of new molecular catalysts for the activation and transformation Of inactive aromatics: