New Organic Radical Reactions

拟议的工作和意义：N-杂环卡宾硼烷(NHC)已被证明具有弱的B-H键，因此在黄药还原中表现为自由基氢原子供体。一类新的硼自由基NHC-硼基已被证明是这些反应的中间体。这项早期工作提出了许多问题：对于自由基反应来说，最好的NHC-硼烷试剂是什么？NHC硼烷能否取代氢化锡，成为长期以来难以捉摸的自由基还原(廉价、低分子、绿色、易分离等)的“理想”介体？新的硼烷，特别是新的硼基的结构和反应活性是什么？这些和其他基本问题将通过合成具有各种NHC和B取代基的各种新的NHC-硼烷并表征它们的结构和反应来解决。最有希望的化合物将被用作黄药、卤化物和假卤化物的自由基还原试剂，用于新的自由基氢化反应，以及作为自由基聚合的辅助引发剂。最重要的自由基的结构将通过电子顺磁共振(EPR)光谱来探测，该光谱也将与其他工具一起用于动力学测量。更广泛的影响：从长远来看，该项目将在两个领域产生社会效益。首先，有机合成是一门中心学科，通过为研究和销售提供新的分子和材料，为大多数生物和物理科学的发展做出了贡献。这项工作的概念和方法深化和拓宽了合成学科，并帮助它为依赖它取得进展的其他领域提供所需的反应和技术。其次，这个项目在推进科学前沿的同时，促进了从事日常研究工作的不同本科生和研究生群体的教学、培训和学习，这一项目具有很强的耦合性。他们进入工作场所，成为推动许多领域进步的人力资本，这些领域对我们公民的健康和我们国家的经济至关重要。该项目还经常使用视频会议等尖端技术来管理洲际合作。这些合作将该提案的教学/培训影响从匹兹堡扩大到法国的巴黎和穆尔豪斯、苏格兰的圣安德鲁斯和日本的东京。

Proposed work and Significance: N-heterocyclic carbene boranes (NHC boranes) have been shown to have weak B-H bonds and accordingly behave as radical hydrogen atom donors in xanthate reductions. A new class of boron radical, the NHC-boryl radical, has been demonstrated to be an intermediate in these reactions. This early work raises many questions: What are the best NHC-borane reagents for radical reactions? Can NHC boranes replace tin hydrides as the long-elusive "ideal" mediators of radical reductions (inexpensive, low molecular weight, green, easy to separate, etc.)? What are the structures and reactivities of the new boranes and especially the new boryl radicals? These and other fundamental questions will be addressed by synthesizing diverse new NHC-boranes with assorted NHC and boron substituents and characterizing their structures and reactions. The most promising compounds will be used as reagents for radical reductions of xanthates, halides and pseudohalides, for new radical hydroborations, and as coinitiators in radical polymerizations. The structures of the most important radicals will be probed by electron paramagnetic resonance (EPR) spectroscopy, which will also be used along with other tools for kinetic measurements. Broader Impact: Societal benefits from this project accrue over the long term in two areas. First, organic synthesis is a central discipline that contributes to the development of most biological and physical sciences by providing new molecules and materials for study and sale. The concepts and methods of this work deepen and broaden the discipline of synthesis and help it in its quest to provide the needed reactions and technologies for other fields that rely on it to progress. Second, there is a strong coupling on this project of advancing the frontiers of science while at the same time promoting teaching, training and learning of the diverse group of undergraduate students and graduate students who do the day-today research work. They move into the workplace to become the human capital that drives progress in many areas that are vital to the health of our citizenry and the economy of our nation. The project also regularly uses cutting edge technology like videoconferences to manage the intercontinental collaborations. These collaborations expand the teaching/training impact of the proposal from Pittsburgh to Paris and Mulhouse in France, St. Andrews in Scotland, and Tokyo in Japan.