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

这个项目是由化学部催化计划资助的。俄亥俄州立大学的克里斯汀·托马斯博士正在开发使用廉价的富含地球的金属的金属催化剂。这种方法涉及金属和与金属结合的磷原子之间的合作。实施更高效、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。大型工业催化剂最常见的来源是钯、铂、铑或铱等金属。这些金属通常被称为“贵金属”，因为它们成本高，地球丰度低。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来取代这些催化剂中的贵金属，如锰、铁、钴、镍和铜。然而，以这些金属为特色的催化剂的开发一直具有挑战性，因为这些金属往往不愿经历建立和破坏化学键所需的复杂化学过程。通过积极地让金属和磷原子参与化学键的裂解和形成，这些障碍可能会被克服，从而开发出更可持续、经济和环境友好的催化过程。通过这个项目，托马斯博士为本科生和研究生提供严格的科学研究培训。托马斯博士还积极参与了面向K-12项目的外联活动、关于催化和可持续性重要性的公共论坛，以及鼓励和支持妇女在STEM职业生涯中的努力。Thomas正在开发一种新的策略，利用金属-配体的协作性，通过最终的催化应用来促进sigma键的激活过程。事实证明，这种类型的合作方法在促进使用富含地球的过渡金属的反应方面特别有效，这些金属往往受到它们自己能够执行的反应范围的限制。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。配基通过基于配基的氧化还原活性或通过配基参与异解的Sigma键裂解事件参与Sigma键的激活过程，至少减轻了过渡金属上的部分氧化还原要求。Thomas博士正在研究N-杂环膦(NHP)和磷(NHP-)配体及其过渡金属络合物，使用螯合型双膦钳形配体框架来加强金属配位并赋予所得络合物稳定性。当结合到刚性的螯合框架中时，NHP膦离子可以被还原为它们的阴离子NHP形式，从而允许发生进一步的基于配体的氧化还原过程。NHP/-配体的独特性质使其能够直接参与双功能sigma键的活化过程。一系列完整的第一排过渡金属络合物正在调查中，其反应性和催化应用的研究正在进行中。为了支持该项目更广泛的影响，Thomas博士积极参与了面向K-12项目的外展活动、关于催化和可持续性重要性的公共论坛，以及鼓励和支持STEM职业女性的努力。该奖项反映了NSF的法定使命，并通过使用基金会的智力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.