High-Valent Tetragonal Late Metal Oxo and Nitrido Complexes

在化学系化学催化计划的支持下，圣母大学的赛斯·布朗教授和他的研究团队将研究使金属配体多键制备和稳定的因素。虽然化合物中的所有原子都通过键结合在一起，但并不是所有的键都是平等的。有些键，如碳-氧键，很强，在自然界中随处可见。其他的，包括晚过渡金属，如Ir与氧或氮原子之间的多个键，即所谓的Ir-氧或-氮键，是罕见的。它们之所以令人感兴趣，既是因为它们的稀缺性，也是因为它们可能具有足够的活性，有助于形成新的化学键，从而充当催化剂或试剂，促进更清洁和更有效的有用物质的制备。支撑这些研究的工作假设是，金属-氮键可能比之前认为的更稳定，困难在于找到了准备它们的方法。相比之下，金属-氧键可能只有在Ir原子周围有其他设计的基团的情况下才是稳定的。布朗博士还将致力于开发新的材料和方法，帮助教授有关反应速率(化学动力学)的化学原理，使广大听众能够理解和吸引他们。这将包括开发可以用现成的家用材料进行的实验，以及使用手机摄像头来测量颜色随时间的变化的方法。在这个项目中，圣母大学的塞斯·布朗教授和他的团队将开发合成方法来合成晚期过渡金属(如Ir)的末端氧和氮的络合物。这种化合物很少见，而且在未知的四方(八面体或正方形金字塔)环境中，由于所谓的“氧代壁”，源于它们在可接近的氧化态中的高d电子计数。氮化物实际上将被氮配体充分稳定到以+7氧化态存在的假设，迄今为止被认为是无法达到的，将使用辅助配体来追求，这些辅助配体要么是氧化还原活性的，允许Ir从常见的Ir(III)氧化态(亚氨二甲苯、杯[4]吡咯烷)跳跃，要么是稳定不常见的Ir(V)前体(烷基或芳基)的配体。将使用能够电子稳定氧化Ir部分的亚氨基或二氧杂环烯配体来寻找氧并化合物。任何可能产生的氧或氮化合物都将经过物理表征以阐明它们的成键，并将分析它们与有机底物的反应性，以了解如何使用新的电子结构来实现有用的氧化。该奖项反映了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 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.