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

在化学系化学合成计划的支持下，印第安纳大学-普渡大学印第安纳波利斯分校的S·巴斯蒂安·劳莱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-受体复合体”，使它们能够调节碳-碳键的组装，或者破坏碳-氧键。属于第一类的工艺对药剂、农用化学品和其他具有重要社会意义的产品的生产是有用的，正在进行的方法可能提供一种替代目前依赖使用稀有和/或有毒金属物种的技术。第二类过程将用于分解生物质衍生的分子，如木质素，将通常被视为农业废弃物的物质转化为可再生和有价值的碳源，从而潜在地减少对化石碳源的依赖。随着Laulhé博士和他的同事团队开展一系列活动，包括提供激励和教育研究经验，为本科生在STEM(科学、技术、工程和数学)工作中的职业生涯做好更好的准备，该奖项的更广泛影响延伸到社会积累的利益。所获得的资金还将使Laulhé博士能够继续为视障学生开发有机化学课程，这些努力的结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影响氢原子转移的芳基自由基物种来解决这一问题，这些自由基物种在可见光介导的电子给体-受体(EDA)络合物的可见光激发下释放，这些络合物是由容易产生的碳负离子(例如氨基乙酸烯醇酸盐)和卤代芳烃组成的。这项研究的一个主要目的是应用这一原理通过位置选择性的直接C-H官能化来获得非正则氨基酸衍生物，并通过使用特定的反离子和/或使用手性有机催化剂来操纵自由基-自由基耦合步骤的过渡态，从而使这种转化成为非对映选择性的。该资助项目的第二部分将利用EDA溶剂阴离子(例如二羟甲基阴离子)和含芳烃的醚的络合物，在可见光照射下促进选择性的C-O键断裂。在这种情况下，电子给体和电子受体之间的电子参数的调节将使复杂的保护醇的选择性脱苄和木质纤维生物质的解聚成为可能。对于C-H键的官能化和C-O键的裂解，许多重要的(和无重金属的)新方法可能会从这项研究计划中涌现出来，对所述目标的追求将进一步加深EDA复杂光化学的基础知识。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 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.