High-Valent Tetragonal Late Metal Oxo and Nitrido Complexes

在化学系化学催化项目的支持下，圣母大学的Seth Brown教授和他的研究团队将研究使金属配体多键的制备和稳定的因素。虽然化合物中的所有原子都是通过化学键结合在一起的，但并不是所有的化学键都是一样的。有些键，比如碳-氧键，很牢固，在自然界中随处可见。其他的，包括后期过渡金属如铱和氧或氮原子之间的多重键，即所谓的铱-氧或-氮键，是罕见的。它们之所以令人感兴趣，一方面是因为它们的稀缺性，另一方面是因为它们可能具有足够的活性，可用于形成新的化学键，从而充当催化剂或试剂，促进更清洁、更有效地制备有用物质。支撑这些研究的工作假设是，金属-氮键可能比以前认为的更稳定，困难在于找到制备它们的方法。相反，金属-氧键只有在铱原子周围有其他设计好的基团时才能稳定。布朗博士还将致力于开发新的材料和方法，以帮助教授有关反应速率（化学动力学）的化学原理，这些方法将被广泛的受众所接受和参与。这将包括开发可以用现成的家庭材料进行的实验，并研究出使用手机相机测量颜色随时间变化的方法。在这个项目中，塞思·布朗教授和他在圣母大学的团队将开发后期过渡金属（如铱）的末端氧和氮络合物的合成方法。这样的化合物是罕见的，并且在四方（八面体或方形金字塔）环境中未知，由于所谓的“氧壁”起源于它们在可到达的氧化态中的高电子计数。假设氮化铱实际上会被氮配体充分稳定，存在于+7氧化态，迄今为止被认为是无法实现的，将使用辅助配体来实现，要么是氧化还原活性，允许铱从普通的铱（III）氧化态（亚胺氧烯，calix[4]吡啶烷）跳跃，要么是稳定不常见的铱(V)前体（烷基或芳基）。氧化合物将使用亚氧羰基或二氧羰基配体来寻找，这些配体能够电子稳定氧铱部分。可以生成的任何氧或氮化合物都将受到物理表征以阐明它们的键合，并且它们与有机底物的反应性将被分析，以了解如何使用新的电子结构来影响有用的氧化。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。

With support from the Chemical Catalysis Program of the Division of Chemistry, Professor Seth Brown and his research team of the University of Notre Dame will study the factors that enable the preparation and stabilization of metal ligand multiple bonds. While all atoms in chemical compounds are held together by bonds, not all bonds are created equal. Some bonds, such as carbon-oxygen bonds, are strong and found everywhere in Nature. Others, including multiple bonds between late transition metals such as iridium and oxygen or nitrogen atoms, so-called iridium-oxo or -nitrido bonds, are rare. They are interesting both because of their scarcity and because they are likely to be reactive enough to be useful in forming new chemical bonds and thus acting as catalysts or reagents to promote cleaner and more efficient preparation of useful substances. The working hypothesis underpinning these studies is that the metal-nitrogen bonds may be more stable than previously believed, with the difficulty being in finding ways to prepare them. In contrast, the metal-oxygen bonds may only be stable if the iridium atoms have other designed groups surrounding them. Dr. Brown will also work to develop new materials and approaches to help teach chemical principles about the rates of reactions (chemical kinetics) in ways that will be accessible and engaging to a wide audience. This will include developing experiments that can be conducted with readily available household materials, and working out ways to measure color changes over time using cell phone cameras.In this project, Professor Seth Brown and his team at Notre Dame will develop synthetic approaches to terminal oxo and nitrido complexes of late transition metals such as iridium. Such compounds are rare, and in tetragonal (octahedral or square pyramidal) environments unknown, due to the so-called “oxo wall” originating in their high d electron count in accessible oxidation states. The hypothesis that iridium nitrides will actually be sufficiently stabilized by the nitrido ligand to exist in the +7 oxidation state, heretofore deemed inaccessible, will be pursued using ancillary ligands that are either redox-active, allowing the iridium to jump from a common iridium(III) oxidation state (iminoxolenes, calix[4]pyrrolides) or ones that stabilize an uncommon iridium(V) precursor (alkyls or aryls). Oxo compounds will be sought using iminoxolene or dioxolene ligands capable of electronic stabilization of the oxoiridium moiety. Any oxo or nitrido compounds that can be generated will be subjected to physical characterization to illuminate their bonding, and their reactivity with organic substrates will be analyzed to see how the novel electronic structures can be used to effect useful oxidations.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.