CAS: Development of Multidentate Ligands that Incorporate Metal-Ligand Cooperativity into Catalytic Hydrofunctionalization Reactions

在化学系化学催化项目的支持下，俄亥俄州立大学的克里斯汀·托马斯教授正在研究用于加氢功能化反应的新型、更可持续的催化剂的基本设计。催化加氢功能化反应提供了一种环境友好的方法，可以将广泛可用的化学原料转化为合成中间体，这些中间体可以很容易地转化为用于制药、消费品和商品化学工业的附加值产品。该项目旨在发现新的催化剂，这些催化剂可以很容易地从天然丰富且廉价的前体中生产出来，特别是利用地球上丰富的金属，如锰、铁和钴。该项目直接有助于对研究生和本科生进行严格的培训，为他们作为科学研究人员的职业生涯做准备。为了增加代表不足的群体在化学领域的参与，Thomas教授担任俄亥俄州立大学女性化学学生组织(女性化学联合科学家，Focus)的教师顾问，是NOBCChE(全国黑人化学家和化学工程师职业促进组织)合作组织的活跃成员，并将在俄亥俄州立大学化学和生物化学部推出一个新的夏季本科项目，专门致力于为代表不足的少数族裔学生(CONVERER，协作性NOBCCHE典型的本科生研究经验)提供研究机会。在化学系化学催化项目的支持下，俄亥俄州立大学的克里斯汀·托马斯教授正在研究新的多齿配体框架的设计，以努力促进金属-配体与地球上丰富的第一排过渡金属(如铁、钴、锰)的合作。该项目旨在发现更可持续的催化方法，将金属-配体合作过程作为一种战略，在不依赖于第一排金属通常无法获得的两电子氧化还原循环的情况下建立和断开化学键。配基设计是这个项目的核心，Thomas小组正在评估这方面的几种不同方法。一种具有N-杂环磷化物片段的基于PPP的三齿钳形配体被证明积极参与金属-配体合作反应，在该反应中，Sigma键被跨金属-磷化物键断裂，正在进行的研究集中于扩展已建立的化学计量反应并将其纳入不饱和底物的氢硼化、氢化和氢化硅氢化的催化循环中。此外，托马斯的研究小组正在探索一种新的基于PNNP的四齿配体，该配体包含两个酰胺供体作为金属-配体协同作用的潜在位点。这一配体与铁、钴和锰的配位以及生成的(PNNP)M化合物对底物(如氢、硅烷和硼烷)跨两个金属-酰胺键的活化作用的化学计量反应性正在研究中，最终目标是将这些基本反应步骤纳入催化氢功能化反应。最后，一个新发现的消除和取代膦取代基的金属模板程序将被用来合成一个扩大的配体家族，包括以磷化物和酰胺供体为潜在反应中心的四齿配体衍生物，具有更多富含电子的烷基取代基的PPP和PNNP配体，以及用于不对称催化的具有P-手性官能团的三齿和四齿配体。新的合成方法将为该领域的研究人员提供一种新的经济和直接的方法来合成包括P-手性变体在内的大家族的多齿配体衍生物，而不需要昂贵的前体。这一奖项反映了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 Christine Thomas at Ohio State University is studying the fundamental design of new, more sustainable, catalysts for hydrofunctionalization reactions. Catalytic hydrofunctionalization reactions provide an environmentally friendly method to convert widely available chemical feedstocks into synthetic intermediates that can easily be converted into value-added products with uses in pharmaceuticals, consumer products, and the commodity chemical industry. The project aims to uncover new catalysts that are easily produced from naturally abundant and inexpensive precursors, particularly taking advantage of Earth-abundant metals such as manganese, iron, and cobalt. This project is directly contributing to the rigorous training of both graduate students and undergraduate researchers in preparation for their careers as scientific researchers. In efforts to increase the participation of underrepresented groups in chemistry, Professor Thomas serves as the faculty advisor to the student organization for women in chemistry at Ohio State (Females of Chemistry Uniting Scientists, FOCUS), is an active member of the NOBCChE (National Organization for the Professional Advancement of Black Chemists and Chemical Engineers) Collaborative, and will be launching a new summer undergraduate program in the Ohio State Department of Chemistry and Biochemistry specifically focused on providing research opportunities for underrepresented minority students (CoNQUER, Collaborative NOBCChE Quintessential Undergraduate Experience in Research). With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Christine Thomas at Ohio State University is studying the design of new multidentate ligand frameworks in an effort to promote metal-ligand cooperativity with Earth-abundant first row transition metals (e.g., iron, cobalt, manganese). The project aims to uncover more sustainable catalytic methods by using metal-ligand cooperative processes as a strategy to make and break chemical bonds without relying on two-electron redox cycles that are often inaccessible to first row metals. Ligand design is at the heart of this project, and the Thomas group is evaluating several different approaches in this regard. A tridentate PPP-based pincer ligand featuring an N-heterocyclic phosphide fragment has been shown to actively participate in metal-ligand cooperative reactions in which sigma bonds are cleaved across the metal-phosphide linkage, and ongoing studies focus on the expansion of established stoichiometric reactions and their incorporation into catalytic cycles for the hydroboration, hydrogenation, and hydrosilylation of unsaturated substrates. In addition, Thomas’s research team is exploring a new tetradentate PNNP-based ligand that contains two amide donors as potential sites for metal-ligand cooperativity. The coordination of this ligand to Fe, Co, and Mn and the stoichiometric reactivity of the resulting (PNNP)M compounds towards the activation of substrates such as hydrogen, silanes, and boranes across the two metal-amide bonds is under investigation, with the ultimate goal of incorporating these fundamental reaction steps into catalytic hydrofunctionalization reactions. Lastly, a newly discovered metal-templated procedure for the elimination and substitution of phosphine substituents will be leveraged to synthesize an expanded family of ligands, including tetradentate ligand derivatives that feature both phosphide and amide donors as potential reactive sites, PPP- and PNNP-based ligands with more electron-rich alkyl substituents, and tridentate and tetradentate ligands with P-chiral functionalities for use in asymmetric catalysis. The new synthetic method will provide researchers in the field with a new economical and straightforward method to synthesize large families of multidentate ligand derivatives including P-chiral variants without the need for expensive precursors.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.