Aryl-aryl bond formation is one of the most important tools in modern organic synthesis. Therefore, there is a high level of interest to develop green, effective reaction system to obtain biaryls. This review summarized the recent advances in the metal-catalyzed Ullmann reaction in which the aryl-aryl bond was formed directly. Furthermore, different types of catalytic mechanisms, especially the surface reaction, have been summarized to help the design of the catalyst.

中文翻译：

---

乌尔曼反应形成的芳基-芳基键：从机理到催化剂

芳基-芳基键的形成是现代有机合成中最重要的工具之一。因此，对于开发绿色，有效的反应体系以获得联芳基具有很高的兴趣。这篇综述总结了金属催化的Ullmann反应的最新进展，其中直接形成了芳基-芳基键。此外，已总结了不同类型的催化机理，特别是表面反应，以帮助催化剂的设计。