Metalla-NHCs: Modular, Redox-Active Ligands for Next Generation Catalysts

在化学系化学合成（SYN）项目的支持下，明尼苏达大学双城分校的Ian Tonks教授将研究新型金属基碳配体的设计和合成，这种配体被称为金属- nhcs （n -杂环碳），可用于可切换的催化反应。这项工作的一个关键创新是，这些配体是第一个将金属结合到游离碳环骨架中的结构例子，后者是一种典型的高活性碳形式。这些新的配体可以直接将电子变化传递给催化活性金属中心，有可能使有机金属化学家开发出具有前所未有的反应结果精确控制水平的新催化剂。对新型可调金属- nhc及其相关配体的基础研究对全球化学催化领域的持续创新至关重要。此外，自唐克斯研究小组成立以来，以学生为主导的自下而上的化学品安全工作的创新一直是其不可或缺的一部分，这笔赠款将通过利用由明尼苏达大学双城分校和北卡罗来纳大学教堂山分校联合创办的安全网站“安全网”，支持将当地成功的安全倡议转化为国家舞台。具体来说，唐克斯教授将扩大他们对学习经验报告的使用，这些报告是学术实验室中侥幸成功或事故的例子，并将其纳入一个公开可用（并可编辑）的数据库。当新的研究人员学习在化学实验室中进行危害评估时，这个数据库将对他们有用。该项目的总体目标是利用唐克斯集团报告的第一个包含双环戊二烯钛部分的游离金属碳复合物的例子。本提案旨在利用钛类似物的合成策略合成一套其他早期过渡金属金属卡宾配合物。具体来说，将探讨低价早期过渡金属与碳二亚胺反应的倾向，其中将描述碳二亚胺的kappa-2与eta-2键的空间和电子要求。此外，金属甲脒配合物的去质子化将用于获得不能通过还原途径获得的衍生物。这些金属卡宾配合物的电子结构将通过结合光谱和电化学技术以及计算建模进行深入研究。最后，将开发金属- nhc配合物的配位化学，特别关注将它们作为其他催化活性金属中心的强氧化还原活性配体。最后，本研究的重点是合成新的氧化还原活性配体，用于催化应用，如聚合，并阐明随后的双金属配合物中的金属-金属相互作用，并着眼于可切换的催化应用。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 the support of the Chemical Synthesis (SYN) Program in the Division of Chemistry, Professor Ian Tonks of the University of Minnesota – Twin Cities will study the design and synthesis of new metal-based carbene ligands called metalla-NHCs (N-heterocyclic carbenes) that can be used for switchable catalytic reactions. A key innovation of this work is that these ligands are the first examples of structures that incorporate metals into the cyclic backbone of a free carbene, the latter being a typically highly reactive form of carbon. These new ligands can directly communicate electronic changes to a catalytically active metal center, potentially allowing organometallic chemists to develop new catalysts with unprecedented levels of precision control of reaction outcomes. Fundamental studies into new classes of tunable metalla-NHC and related ligands are critical for continued innovation in the global chemical catalysis field. Additionally, innovation in student-led bottom-up chemical safety efforts has been an integral part of the Tonks Research Group since its inception, and this grant will support translating locally-successful safety initiatives to the national stage by leveraging The Safety Net, a safety website jointly founded by the University of Minnesota – Twin Cities and the University of North Carolina – Chapel Hill. Specifically, Professor Tonks will expand their use of Learning Experience Reports, examples of near-misses or accidents in academic labs, into a publicly available (and editable) database. This database will be useful for new researchers as they learn to carry out hazard assessments in chemistry laboratories.The overarching goal of this project is to capitalize on the Tonks Group’s report of the first example of a free metallacarbene complex containing a dicyclopentadienyltitanium moiety. This proposal aims to synthesize a suite of other early transition metal metallacarbene complexes using the synthetic strategies developed for the titanium analogue. Specifically, the propensity of low valent early transition metals to react with carbodiimides will be explored, where the steric and electronic requirements for kappa-2 versus eta-2 bonding of the carbodiimide will be delineated. Further, the deprotonation of metal-formamidine complexes will be used to access derivatives that cannot be accessed via reductive routes. The electronic structure of these metallacarbene complexes will be studied in depth through combined spectroscopic and electrochemical techniques, as well as computational modeling. Finally, the coordination chemistry of the metalla-NHC complexes will be developed, with a specific focus on using them as strong, redox active dative ligands for other catalytically active metal centers. Ultimately, this research is focused on synthesizing new suites of redox active ligands for catalysis applications such as polymerizations, and elucidating metal-metal interactions in subsequent bimetallic complexes with an eye toward switchable catalytic applications.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.