Sigma-Bond Activation and Catalysis Facilitated by Metal-Phosphorus Ligand Cooperativity

本项目由化学学部催化项目资助。俄亥俄州立大学的克里斯汀·托马斯博士正在利用地球上储量丰富的廉价金属开发金属催化剂。这种方法涉及金属和与金属结合的磷原子之间的合作。实施更有效、更经济、更环保的催化剂技术是开发更可持续的燃料、商品化学品和消费品生产工艺的关键。大规模工业催化剂最常见的原料是钯、铂、铑或铱等金属。这些通常被称为“贵金属”，因为它们的高成本和低地球丰度。一个更好的解决方案是用经济上更可行的地球上丰富的金属，如锰、铁、钴、镍和铜，来取代这些催化剂中的贵金属。然而，以这些金属为特征的催化剂的开发一直具有挑战性，因为这些金属通常不愿经历建立和破坏化学键所需的复杂化学过程。通过积极参与金属和磷原子的裂解和化学键的形成，可以克服这些障碍，从而开发出更可持续、更经济、更环保的催化过程。通过这个项目，托马斯博士为本科生和研究生提供了严格的科研训练。托马斯博士还积极参与面向K-12课程的外展活动，关于催化和可持续性重要性的公共论坛，以及鼓励和支持女性从事stem职业的努力。Thomas正在开发一种新的策略来促进sigma键活化过程，并利用金属配体的协同性进行最终的催化应用。这种类型的合作方法已被证明对促进利用地球上丰富的过渡金属的反应特别有效，这些过渡金属通常在它们自己可以进行的反应范围内受到限制。这种限制源于地球上丰富的过渡金属，如锰、铁、钴、镍和铜，不愿经历多电子氧化还原变化。配体参与西格玛键激活过程，无论是通过基于配体的氧化还原活性，还是通过配体参与异裂西格玛键裂解事件，至少减轻了对过渡金属的部分氧化还原要求。Thomas博士正在研究n -杂环磷（NHP+）和磷（NHP-）配体及其过渡金属配合物，使用螯合二膦螯合配体框架来加强金属配位并赋予所得到的配合物稳定性。当纳入刚性螯合框架时，NHP+磷离子可以还原为阴离子NHP-形式，允许进一步的基于配体的氧化还原过程发生。NHP+/-配体的独特性质允许它们直接参与双功能sigma键激活过程。一系列完整的第一行过渡金属配合物正在研究中，其反应性和催化应用的研究正在进行中。为了支持该项目的更广泛影响，托马斯博士积极参与面向K-12课程的外展活动，关于催化和可持续性重要性的公共论坛，以及鼓励和支持女性从事STEM职业的努力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project is funded by the Catalysis Program of the Chemistry Division. Dr. Christine Thomas of The Ohio State University is developing metal catalysts using inexpensive Earth-abundant metals. The approach involves cooperation between the metal and a phosphorus atom bound to the metal. Implementing more efficient, economical and environmentally friendly catalyst technologies is the key to developing more sustainable processes for the production of fuels, commodity chemicals, and consumer products. Large scale industrial catalysts are most commonly derived from metals such as palladium, platinum, rhodium, or iridium. These are often referred to as "precious metals" owing to their high cost and low Earth-abundance. A better solution is to replace the precious metals in these catalysts with more economically viable Earth-abundant metals such as manganese, iron, cobalt, nickel, and copper. However, the development of catalysts featuring these metals has been challenging because such metals are often reluctant to undergo the complex chemical processes required to make and break chemical bonds. By actively involving both the metal and the phosphorus atom in the cleavage and formation of chemical bonds, these obstacles may be overcome, allowing more sustainable, economical, and environmentally friendly catalytic processes to be developed. Through this project Dr. Thomas is providing rigorous training in scientific research for both undergraduate and graduate students. Dr. Thomas is also actively involved in outreach activities geared towards K-12 programs, public forums on the importance of catalysis and sustainability, and efforts to encourage and support women in careers in STEM.Dr. Thomas is developing a new strategy for promoting sigma-bond activation processes with ultimate catalytic applications using metal-ligand cooperativity. Cooperative approaches of this type have proven particularly effective for facilitating reactions using Earth-abundant transition metals, which are often limited in the range of reactions they can perform on their own. This limitation stems from the reluctance of Earth-abundant transition metals such as manganese, iron, cobalt, nickel, and copper to undergo multi-electron redox changes. Participation of a ligand in sigma-bond activation processes, either via ligand-based redox activity or by ligand involvement in heterolytic sigma-bond cleavage events, alleviates at least some of the redox requirements on the transition metal. Dr. Thomas is investigating N-heterocyclic phosphenium (NHP+) and phosphido (NHP-) ligands and their transition metal complexes using a chelating diphosphine pincer ligand framework to enforce metal coordination and impart stability upon the resulting complexes. When incorporated into a rigid chelating framework, NHP+ phosphenium cations can be reduced to their anionic NHP- form, allowing for further ligand-based redox processes to occur. The unique properties of NHP+/- ligands allows them to participate directly in bifunctional sigma-bond activation processes. A complete series of first row transition metal complexes is under investigation and studies of their reactivity and catalytic applications are ongoing. In support of the broader impacts of this project, Dr. Thomas is actively involved in outreach activities geared towards K-12 programs, public forums on the importance of catalysis and sustainability, and efforts to encourage and support women in careers in STEM.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.