CAS: Enabling Synthesis through Small Molecule Liberation

在化学系化学催化计划的支持下，堪萨斯大学的Jon Tunge教授正在研究利用分子中的固有能量来实现新的环境可持续化学制造过程的策略的开发。具体地说，从简单的原料中释放稳定的小分子(二氧化碳和/或氢)，有时与收集光能相结合，将提供推动化学反应的能量，而不需要传统的、更浪费的能量输入方法。为了进一步减少正在设计的化学工艺对环境的影响，将使用基于地球上丰富的钴金属的催化剂作为反应促进剂，以取代传统的昂贵的贵金属。这些新催化剂还将允许设计新类型的反应路径。预计所开发的方法将适用于各种材料的合成，这些材料具有潜在的应用，如药剂、农用化学品和其他对科学、工程和商业有价值的物质。这个资助项目的更广泛的影响延伸到了为社会带来的好处，因为Tunge教授和他的同事们参与了旨在将这项研究的目标与培训和招聘计划相结合的外展和教育活动，这些培训和招聘计划包含了促进绿色化学原则的内容。这些活动的一个重要目标将是开展外联活动，教育K-12区的学生了解他们日常环境中发生的共同化学，并将这些观测数据与可持续化学中的当代挑战联系起来。另一个目标是利用这些社区联系来吸引来自不同背景的学生，包括属于STEM(科学、技术、工程和数学)领域代表性不足的群体的个人，从事解决可持续发展关键问题的职业。资助的项目侧重于开发基于通过C-C和C-H键裂解催化生成活性中间体的化学转化。正在开发的催化途径利用脱羧化为直接从廉价的羧酸原位生成合成有用的活性中间体提供了一种有效的策略。正在研究的其他工艺利用析氢反应实现原子经济功能化。钴催化剂在脱羧基偶联反应中取代了传统的昂贵的钯催化剂，预计将允许新的转化类型，而这些类型是目前技术无法实现的。此外，光氧化还原催化的放氢将允许氨基酸和多肽的特定部位功能化，同时也使区域控制的脱羧基Heck样酰化和区域化学互补的烯丙化成为可能。串联执行这些新的转换将进一步允许通过时间和动力学控制的迭代脱羧基偶联来构建复杂分子。正在进行的研究将为合成化学家提供一个通用的范例，用于在温和的条件下访问活性物种，同时产生最少的废物：(1)用于过渡金属催化剂氧化还原洗牌的可见光光氧化还原催化剂，以及(2)通过释放最小分子氢来允许氧化偶联的放氢。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, Professor Jon Tunge of the University of Kansas is studying the development of strategies that utilize the innate energy in molecules to enable new environmentally sustainable processes for chemical manufacturing. Specifically, the liberation of small stable molecules (carbon dioxide and/or hydrogen) from simple feedstocks, sometimes in combination with harvesting light energy, will provide the energy to drive chemical reactions without the need for traditional, more wasteful, methods of energy input. To further lessen the environmental impact of the chemical processes being designed, catalysts based on earth-abundant cobalt metal will be utilized as reaction promoters in lieu of traditional expensive noble metals. These new catalysts will also allow the design of new types of reaction pathways. It is anticipated that the methods developed will be applicable to the synthesis of a wide variety of materials with potential applications as pharmaceutical agents, agrochemicals, and other substances of value to science, engineering, and commerce. The broader impacts of the funded project extend to the benefits accrued to society as Professor Tunge and his coworkers engage in outreach and educational activities designed to integrate the goals of this research with training and recruitment programs that incorporate the promotion of 'green chemistry' principles. A significant goal of these activities will be to engage in outreach to educate area K-12 students on common chemistry that occurs in their everyday environment and to connect these observables to contemporary challenges in sustainable chemistry. A further goal is to utilize these community connections to attract students from diverse backgrounds, including individuals belonging to groups underrepresented in STEM (science, technology, engineering and mathematics) fields, to careers that address critical issues of sustainability.The funded project is focused on the development of chemical transformations based on the catalytic generation of reactive intermediates via the cleavage of C–C and C–H bonds. The catalytic pathways being developed utilize decarboxylation to provide an efficient strategy for the in situ formation of synthetically useful reactive intermediates directly from inexpensive carboxylic acids. Other processes under investigation utilize the hydrogen evolution reaction for atom-economical functionalization. Cobalt catalysts replace traditional, expensive, palladium catalysts in decarboxylative coupling reactions and are anticipated to allow for new transformation types that are inaccessible using current technologies. Additionally, photoredox-catalyzed hydrogen evolution will allow for the site-specific functionalization of amino acids and peptides, while also enabling regiocontrolled decarboxylative Heck-like acylations and regiochemically complementary allylations. Performing these new transformations in series will further allow construction of complex molecules through temporally- and kinetically-controlled iterative decarboxylative couplings. The ongoing studies will advance a general paradigm for synthetic chemists to use for accessing reactive species under mild conditions, while generating minimal waste using: (1) visible light photoredox catalysts for redox shuffling of transition metal catalysts, and (2) hydrogen evolution to allow oxidative couplings through liberation of the smallest molecule, hydrogen.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.