CAREER: Metal-Free C-C Bond Formation and C-O Bond Cleavage Mediated by Electron-Donor-Acceptor Complexes of Arenes

在化学系化学合成项目的支持下，印第安纳州普渡大学印第安纳波利斯分校的Sébastien Laulhé正在研究新的无重金属工艺，旨在减少化学制造的环境足迹。蓝光被用来激活所谓的“电子-供体-受体复合物”，使它们能够介导碳-碳键的组装或破坏碳-氧键。属于第一类的工艺可用于生产药剂、农用化学品和其他具有社会重要性的产品，并且所追求的方法可以提供依赖于使用稀有和/或有毒金属物质的现有技术的替代方案。第二类工艺将用于分解木质素等生物质衍生分子，将通常被视为农业废物流的物质转化为可再生且有价值的碳源，从而有可能减少对化石碳源的依赖。该奖项的更广泛的影响延伸到社会的利益，因为Laulhé博士和他的同事团队开展了一系列活动，包括提供激励和教育研究经验，以更好地为本科生在STEM（科学，技术，工程和数学）劳动力中的职业生涯做好准备。获得的资金还将使Laulhé博士能够继续为视障学生开发有机化学课程，这些努力的成果将与高等教育界分享。在没有过渡金属的情况下，通过区域选择性C（sp3）-H官能化策略形成碳-碳键仍然是一个挑战。在该项目下进行的研究将通过利用能够实现氢原子转移的芳基自由基物质来解决这个问题，所述芳基自由基物质在可见光介导的容易产生的碳负离子的电子-供体-受体（EDA）络合物的激发下释放（例如，氨基乙酸烯醇盐）和卤代芳烃。该研究的一个主要目标是应用这一原理通过位点选择性直接C-H官能化来获得非规范氨基酸衍生物，并通过使用特定抗衡离子和/或使用手性有机催化剂操纵自由基-自由基偶联步骤的过渡态来使这种转化具有非对映选择性。资助项目的第二部分将利用溶剂阴离子的EDA络合物（例如，dimsyl阴离子）和含芳烃的醚以促进在用可见光照射时的选择性C-O键裂解。在这种情况下，预计电子供体和电子受体之间的电子参数的调整将使得能够选择性地脱苄基的复杂的保护的醇和解聚的木质纤维素生物质。若干重大（和不含重金属的）用于C-H键的官能化和C-O键的裂解的新方法，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.

With the support of the Chemical Synthesis Program in the Division of Chemistry, Sébastien Laulhé of Indiana University-Purdue University Indianapolis is studying new heavy metal-free processes designed to reduce the environmental footprint of chemical manufacturing. Blue light is employed to activate so-called 'electron-donor-acceptor complexes' enabling them to either mediate the assembly of carbon-carbon bonds or else to break carbon-oxygen bonds. Processes belonging to the first class are useful for the generation of pharmaceutical agents, agrochemicals, and other societally important products, and the approach being pursued may provide an alternative to current technologies reliant on the use of rare and/or toxic metal species. The second type of processes will be deployed to break down biomass-derived molecules, such as lignin, to turn what are typically regarded as agricultural waste streams into renewable and valuable sources of carbon, thereby potentially reducing dependence on fossil-based carbon sources. The broader impacts of the award extend to the benefits accrued to society as Dr. Laulhé and his team of coworkers pursue a range of activities, including the provision of stimulating and educational research experiences, to better prepare undergraduate students for careers in the STEM (science, technology, engineering and mathematics) workforce. The funding secured will also enable Dr. Laulhé to continue to develop an organic chemistry curriculum for visually impaired students, the results of these efforts will be shared with the higher education community.The formation of carbon-carbon bonds through regioselective C(sp3)–H functionalization strategies in the absence of transition-metals remains a challenge. The research being pursued under this project will address this problem by utilizing aryl radical species capable of effecting hydrogen-atom transfer that are released upon visible light-mediated excitation of electron-donor-acceptor (EDA) complexes of readily generated carbanions (e.g., aminoacetate enolates) and haloarenes. A major goal of the research is to apply this principle to access non-canonical amino acid derivatives via site-selective direct C-H functionalization and to render such transformations diastereoselective by manipulation of the transition state for the radical-radical coupling step using specific counter ions and/or the use of chiral organocatalysts. The second part of the funded project will exploit EDA complexes of solvent anions (e.g., dimsyl anion) and arene-containing ethers to promote selective C–O bond cleavages upon irradiation with visible light. In this case, it is expected that tuning of the electronic parameters between electron-donors and electron-acceptors will enable selective debenzylation of complex protected alcohols and depolymerization of lignocellulosic biomass. A number of significant (and heavy metal-free) new methods for both the functionalization of C–H bonds and the cleavage of C–O bonds, are likely emerge from this research program and the pursuit of the aims described will further fundamental knowledge of EDA complex photochemistry.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.