CAREER: Nucleophilic Cobalt Photocatalysis for the Generation of Radicals from Non-Traditional Precursors

俄克拉荷马州立大学的Spencer Pitre在化学系化学催化计划和既定的刺激竞争研究计划(EPSCoR)的支持下，正在开发利用可见光照射从非传统前体生成碳自由基的钴催化剂。碳自由基已成为构建复杂有机分子不可缺少的工具。然而，大多数有机化合物必须被预活化才能有效地作为自由基前体，增加了不必要的合成步骤，并产生了更多的副产品和化学废物。受维生素B12及其天然反应性的启发，皮特博士和他的研究小组正在利用类似的钴络合物从新类别的前体中产生碳自由基，从而避免了对预活化底物的需要。这些方法依靠可见光化学来调节自由基的形成，这是一种新兴的合成策略，可以在温和的反应条件下进行。尽管它对有机化学领域很重要，但本科生在传统课程中没有接触到光化学。这一疏漏正在通过一年一度的本科生光化学研讨会得到解决，该研讨会为从俄克拉荷马州各地获得研究机会有限的学生提供机会，了解光化学及其对新化学发展的影响。这些研究工作还将有助于培训一批光化学和催化方面的研究生和本科生研究人员。钴肟模仿维生素B12的钴原子的反应活性，是已知的最强的亲核性之一，当处于Co(I)氧化状态时，可以与亲电体发生SN2反应。当用可见光照射时，生成的烷基钴可以很容易地发生均解裂解，生成以碳为中心的自由基。尽管钴肟具有相似的亲核性，但在催化亲电底物产生自由基方面通常不如维生素B12有效。皮特博士和他的研究团队正在探索轴向配体对催化循环每一步的影响，以开发更高效的亲核钴光催化剂。这些亲核钴光催化剂正在进行调整，以使新类别的前体形成自由基，包括氯仿、缺电子的烯烃、亚胺离子、卤化乙烯和三氟化物。如果成功，这些研究将扩大对钴肟化学的理解，并增强钴(I)钴肟催化系统的开发和部署的潜力。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Catalysis Program in the Division of Chemistry and the Established Program to Stimulate Competitive Research (EPSCoR), Spencer Pitre of Oklahoma State University is developing cobalt catalysts to generate carbon radicals from non-traditional precursors using visible light irradiation. Carbon radicals have become an indispensable tool for the construction of complex organic molecules. However, most organic compounds must be preactivated to be effective as radical precursors, adding undesired synthetic steps and creating additional byproducts and chemical waste. Inspired by Vitamin B12 and its natural reactivity, Dr. Pitre and his research group are leveraging analogous cobalt complexes to generate carbon radicals from new classes of precursors, avoiding the need for preactivated substrates. These methods rely on visible light photochemistry to mediate radical formation, an emerging synthetic strategy that enables mild reaction conditions. Despite its importance to the field of organic chemistry, students at the undergraduate level do not receive any exposure to photochemistry in the traditional curriculum. This omission is being addressed through an annual undergraduate photochemistry workshop, which gives students that have limited access to research opportunities from across Oklahoma the chance to learn about photochemistry and its impact on the development of new chemistries. These research effort will also serve to train a diverse group of graduate and undergraduate researchers in photochemistry and catalysis.Cobaloximes, which mimic the reactivity of the cobalt atom of Vitamin B12, are among the strongest nucleophiles known when in the Co(I) oxidation state and can undergo SN2 reactions with electrophiles. The resulting alkyl–cobalt can undergo facile homolytic cleavage when irradiated with visible light to generate carbon-centered radicals. Despite having similar nucleophilicities, cobaloximes are generally less efficient than Vitamin B12 at catalyzing radical generation from electrophilic substrates. Dr. Pitre and his research team are probing the effect of the axial ligands on each step of the catalytic cycle to develop more efficient nucleophilic cobalt photocatalysts. These nucleophilic cobalt photocatalysts are being tuned to enable radical formation from new classes of precursors, including chloroform, electron-deficient alkenes, iminium ions and vinyl halides and triflates. If successful, these studies will expand understanding of cobaloxime chemistry and enhance the potential for the development and deployment of Co(I) cobaloxime catalytic systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.