High-Valent Metal-Oxo Species: Beyond the Oxo Wall

在NSF化学部化学结构、动力学和机制B计划的资助下，密歇根大学Lehnert教授和Trinity大学Shearer教授的合作研究小组研究了不同的钴和镍基氧代络合物，以提高对这些不稳定物质的结构和电子性质的理解。金属氧物种通常涉及酶催化和合成催化，并在激素生物合成，药物代谢和光合作用中发挥关键作用。在化学和制药工业中，反应性金属-氧代络合物用作催化剂，用于生产化学原料以及精细化学品和药物的合成。目前，科学家们对后过渡金属含氧物种的性质缺乏详细的了解，这些物种在化学催化中显示出巨大的应用潜力，但由于科学家无法很好地控制其反应性而未得到充分利用。Lehnert教授是D-RISE计划的主任，该计划为来自底特律的高中生提供为期7周的全日制夏季研究机会，这些学生属于科学，技术，工程和数学（STEM）学科中代表性不足的少数民族（URM）群体。这些活动包括资助一名高中生参加D-RISE。希勒教授专门与通过旨在增加URM学生参与科学的机制招募的本科生进行研究（特别是Trinity大学的McNair学者计划）。 Lehnert教授和Shearer教授正在开发一些高价Co和Ni-氧代配合物的结构和电子性质的理解。特别是自旋状态对这些配合物的电子性质的影响是低估的，然而，如铁-氧代配合物所示，自旋状态对这些物种的反应性具有关键影响。在Co-氧代配合物的情况下，自旋状态也提供了一个潜在的途径，真正违反了“氧代墙”，这是一个概念，被认为是在高价金属-氧代化学圣杯。金属-氧代配合物的另一个重要的二分法是它们是否最好地表示为金属-氧代或金属-氧基物种的问题，以及这如何影响它们的反应性。因此，对高价Co-和Ni-氧代配合物的基本性质的研究解决了关于高价金属-氧代配合物的许多重要的基本问题，这些问题对这一研究领域具有一般（概念）意义。该研究对于进一步开发用于水氧化和有机分子功能化的第一排后期过渡金属催化剂具有广泛的意义。特别地，用于有机分子官能化的生物启发催化剂作为用于生产化学原料和药物的工业催化剂受到高度追捧。该项目采用了大量的光谱和理论方法，包括电子顺磁共振，磁圆二色性，共振拉曼和X射线吸收光谱。理论方法（密度泛函理论和多参考量子化学计算）用于询问光谱结果，并将其与电子结构和反应性联系起来。Lehnert教授积极参与STEM外展计划，重点是从底特律招募代表性不足的少数民族（URM）高中生到STEM领域。希勒教授的实验室专门与本科（UG）学生合作，这些学生是通过旨在增加URM UG学生参与科学的机制招募的（特别是Trinity大学的McNair学者计划）。这两项活动都支持该项目产生更广泛的影响。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。

With funding from the Chemical Structure, Dynamics and Mechanisms B Program of the NSF Chemistry Division, the collaborative research team of Professor Lehnert of University of Michigan and Professor Shearer of Trinity University investigates different Cobalt- and Nickel-based oxo complexes to improve the understanding of the structural and electronic properties of these unstable species. Metal-oxo species are often implicated in enzymatic and synthetic catalysis and play key roles in hormone biosynthesis, drug metabolism, and in photosynthesis. In the chemical and pharmaceutical industry, reactive metal-oxo complexes are used as catalysts for the production of chemical feedstocks and in the synthesis of fine chemicals and pharmaceuticals. Currently, scientists are lacking a detailed understanding of the properties of late-transition metal oxo species, which show great potential for applications in chemical catalysis, but which are underutilized as scientists cannot control their reactivity well. Professor Lehnert is the director of the D-RISE program, which provides 7-weeks, full-time summer research opportunities to high school students from Detroit that belong to underrepresented minority (URM) groups in science, technology, engineering and math (STEM) disciplines. The activities include funding for one high school student to participate in D-RISE. Professor Shearer conducts research exclusively with undergraduate students recruited through mechanisms that aim at increasing the participation of URM students in the sciences (in particular, Trinity University's McNair Scholar's program). Professor Lehnert and Professor Shearer are developing an understanding of the structural and electronic properties of a number of high-valent Co- and Nickel-oxo complexes. Especially the effect of the spin state on the electronic properties of these complexes is underappreciated; yet, as demonstrated for iron-oxo complexes, the spin state has a pivotal influence on the reactivity of these species. In the case of Co-oxo complexes, spin state also provides a potential pathway for a true violation of the "oxo wall", a concept that is considered a holy grail in high-valent metal-oxo chemistry. Another important dichotomy of metal-oxo complexes is the question of whether they are best represented as metal-oxo or metal-oxyl species, and how this influences their reactivity. Therefore, the research on the fundamental properties of high-valent Co- and Nickel-oxo complexes addresses many important fundamental questions about high-valent metal-oxo complexes with general (conceptual) implications for this area of research. The proposed research has broad implications with respect to further developing late first-row transition metal catalysts for water oxidation and the functionalization of organic molecules. In particular, bioinspired catalysts for the functionalization of organic molecules are highly sought after as industrial catalysts for the production of chemical feedstocks and pharmaceuticals. This project employs a large array of spectroscopic and theoretical methods, including electron paramagnetic resonance, magnetic circular dichroism, resonance Raman, and X-ray absorption spectroscopy. Theoretical methods (density functional theory and multi-reference quantum-chemical calculations) are used to interrogate the spectroscopic results, and connect them to electronic structure and reactivity. Professor Lehnert is actively engaged in STEM outreach programs focused on recruiting underrepresented minority (URM) high school students from Detroit to STEM fields. Professor Shearer's laboratory works exclusively with undergraduate (UG) students, which are recruited through mechanisms that aim at increasing the participation of URM UG students in the sciences (in particular, Trinity University's McNair Scholar's program). Both of these activities support the broader impacts of the project.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.