Metalloradical Catalysis for Selective Radical Reactions

在这个由化学系化学催化计划资助的项目中，南佛罗里达大学的Peter Zhang教授将金属催化的概念应用于开发基于卟啉钴(II)络合物的新催化体系，以控制自由基反应的反应性和选择性。由于金属催化可以在不需要化学计量引发剂(如常用的有机锡试剂)的情况下催化生成自由基中间体，该方法将对环境产生积极的影响。与通常需要稀有且昂贵的第二和第三排金属离子催化两电子离子反应相比，基于地球上丰富且廉价的第一排过渡金属离子(如钴)的催化剂可以有效地进行单电子自由基反应。因此，金属催化剂的发展满足了对可持续催化剂日益增长的需求。张教授提出的项目将研究和教育活动融为一体。除了为研究生和博士后提供科学培训外，还为高中生和教师以及本科生提供了实验室经验。这些新的催化自由基过程在机械上独特，在操作上具有吸引力，是构建有机化合物的宝贵合成工具，如具有生物重要性的天然产物和具有药学意义的小分子。在对基于Co(II)的自由基环丙化和氮杂环化反应的催化机理基本了解的基础上，人们正在开发包括一系列自由基反应的新的催化工艺，以允许有效地构建三元环丙烷和氮杂环丙烷以外的碳环和杂环。通过设计和合成具有潜在氢键能力的手性卟啉，并以可调的电子、空间和手性环境为支撑配体，该项目旨在实现几种特定类型的Co(II)催化的自由基级联过程。该项目的成功可能会促使基于开壳金属离子和手性配体的不同组合的新的金属催化剂体系的确定，这些催化剂可以催化广泛的立体选择性自由基反应。

AbstractIn this project funded by the Chemical Catalysis program of the Chemistry Division, Professor Peter Zhang of the University of South Florida applies the concept of metalloradical catalysis for the development of new catalytic systems based on cobalt(II) complexes of porphyrins to control the reactivity and selectivity of radical reactions. Since metalloradical catalysis can generate radical intermediates catalytically without the need for stoichiometric initiators such as the commonly employed organotin reagents, the method will have a positive environmental impact. In comparison with the typical need for rare and expensive second- and third-row metal ions to catalyze two-electron ionic reactions, one-electron radical reactions can be carried out effectively with catalysts based on earth-abundant and inexpensive first-row transition metal ions such as cobalt. As such, the development of metalloradical catalysis addresses the increasing need for sustainable catalysts. The proposed project by Professor Zhang integrates research and educational activities. In addition to scientific training for graduate and postdoctoral students, laboratory experiences for high school students and teachers, as well as undergraduate students, are provided.These new catalytic radical processes, which are both mechanistically distinctive and operationally attractive, serve as valuable synthetic tools for constructing organic compounds, such as biologically important natural products and pharmaceutically interesting small molecules. On the basis of the fundamental understanding of the catalytic mechanisms of Co(II)-based radical cyclopropanation and aziridination reactions, new catalytic processes that involve a cascade sequence of radical reactions are in development to allow for the efficient construction of carbocycles and heterocycles beyond three-membered cyclopropanes and aziridines. Through the design and synthesis of chiral porphyrins possessing potential hydrogen bonding capability and with tunable electronic, steric, and chiral environments as the supporting ligands, this project aims to achieve several specific types of Co(II)-catalyzed radical cascade processes. The success of this project may prompt the identification of new metalloradical catalyst systems based on different combinations of open-shell metal ions and chiral ligands that can catalyze a broad range of stereoselective radical reactions.