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

该项目由化学部催化计划资助。俄亥俄州州立大学的克莉丝汀托马斯博士正在利用廉价的地球上丰富的金属开发金属催化剂。该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、日用化学品和消费品生产工艺的关键。大规模工业催化剂最通常衍生自金属如钯、铂、铑或铱。由于其成本高和地球丰度低，它们通常被称为“贵金属”。一个更好的解决方案是用更经济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意经历建立和破坏化学键所需的复杂化学过程。通过使金属和磷原子两者积极参与化学键的裂解和形成，可以克服这些障碍，从而允许开发更可持续、经济和环境友好的催化方法。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学研究培训。托马斯博士还积极参与面向K-12计划的外展活动，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。托马斯博士正在开发一种新的战略，用于促进sigma键活化过程，并使用金属配体协同性实现最终的催化应用。这种类型的合作方法已被证明对促进使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，镍和铜不愿意经历多电子氧化还原变化。通过基于配体的氧化还原活性或通过配体参与异裂σ-键裂解事件，配体参与σ-键活化过程，减少了对过渡金属的至少一些氧化还原要求。托马斯博士正在研究N-杂环膦（NHP+）和膦（NHP-）配体及其过渡金属络合物，使用螯合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。当结合到刚性螯合框架中时，NHP+膦阳离子可以被还原成其阴离子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σ键活化过程。一个完整的系列的第一行过渡金属配合物正在调查和研究其反应性和催化应用正在进行中。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计划的外展活动，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NSF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.