Metalloradical Catalysis for Selective Radical Reactions

在化学系化学催化项目资助的这个项目中，南佛罗里达大学的Peter Zhang教授应用金属自由基催化的概念，开发了基于卟啉钴（II）配合物的新催化体系，以控制自由基反应的活性和选择性。由于金属自由基催化可以催化地产生自由基中间体，而不需要化学计量的引发剂，如常用的有机锡试剂，该方法将具有积极的环境影响。与通常需要稀有和昂贵的第二和第三行金属离子来催化双电子离子反应相比，单电子自由基反应可以用基于地球丰富和廉价的第一行过渡金属离子如钴的催化剂有效地进行。因此，金属自由基催化的发展解决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结合起来。除了对研究生和博士后学生进行科学培训外，还为高中生和教师以及本科生提供实验室经验。这些新的催化自由基过程在机理上独特，在操作上具有吸引力，是构建有机化合物（如生物学上重要的天然产物和药学上有趣的小分子）的宝贵合成工具。基于对基于Co（II）的自由基环丙烷化和氮丙啶化反应的催化机理的基本理解，正在开发涉及自由基反应的级联序列的新的催化过程，以允许有效地构建超过三元环丙烷和氮丙啶的碳环和杂环。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，空间和手性环境作为支持配体，本项目旨在实现几种特定类型的Co（II）催化自由基级联过程。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自由基催化剂系统的鉴定，其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.