Development of and Mechanistic Studies on the Palladium and Iron-Cocatalyzed Nucleoboration of Olefins

在化学系化学催化项目的支持下，甲米L.德克萨斯大学奥斯汀分校的船体正在研究一种钯和铁催化的工艺，该工艺将简单的化学原料（烯烃）转化为增值产品。这种所谓的“核硼化”方法导致硼原子和另一种元素（通常为氮）中的一种以精细控制的方式添加到烯烃中。存在选择性转化，随后将硼原子转化为各种各样的其他取代基，整个过程有望成为制造复杂化合物和对社会有价值的先进材料的通用方法。与方法开发相结合，资助的研究包括详细的机理研究，旨在阐明催化剂对如何发挥作用，目的是推进过渡金属催化的基础知识，提高化学合成的效率和可持续性。资助项目的更广泛的影响延伸到社会的利益，因为船体博士和她的同事从事广泛的教育和推广活动，包括：ChemBridge计划旨在提高属于STEM服务不足群体的年轻德克萨斯人的大学准备（科学、技术、工程和数学）领域，并不断努力宣传多样性、公平、和包容性之间的教师和学生的德州大学奥斯汀分校。资助的研究重点是最近发现的钯/铁共催化的烯烃氨基硼化的调查，它的特点是进一步发展的过程（例如，以扩大底物和亲核试剂的范围）和相关的机理研究，以获得对三氟甲磺酸铁（II）助催化剂的潜在作用的了解。具体而言，在方法开发过程中（目标1），将进一步探索并扩展至更具挑战性的烯烃底物，其中可能会在该工艺的Markovnikov加成阶段后发生β-氢化物消除反应，从而成功实现对异戊烯的氨基硼化反应[关键试剂：PhthNH、B2 Pin 2、催化剂Pd（MeCN）2Cl 2、催化剂Fe（OTf）2和O2]。除了基于N的系统之外的亲核试剂，例如基于O的（例如，酚类），S-基（例如，硫醇），和基于C的（例如，吲哚），也将被研究作为替代的金属转移试剂（例如，Si-和Sn-基），以潜在地达到一个高度普遍化的核测量过程。在进一步努力扩大平台的多功能性的过程中，引入了“Pd步移”阶段（即，区域异构化）。在机理研究（目的2），起源的关键作用的铁物种在transmetalation步骤的氨基硼正在探索，因为它是同样奇怪的有益效果的氮杂-瓦克过程。最后，为了开发核硼化过程的更可持续的变体（目标3），正在开发非均相和可回收的Pd/Fe催化剂系统。总而言之，正在进行的研究预计将扩展烯烃双官能化化学的多功能性，并在这样做的过程中，促进重要类别的氮的合成（和其它杂原子）的化合物，其在活性药物成分和其它种类的在科学，工程，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 the support of the Chemical Catalysis Program in the Division of Chemistry, Kami L. Hull of the University of Texas at Austin (UT-Austin) is studying a palladium- and iron-catalyzed process that converts simple chemical feedstocks (olefins) into value-added products. This so-called "nucleoboration" method results in the addition of an atom of boron and one of another element, typically nitrogen, to the olefin in a finely controlled manner. Selective transformations exist to subsequently convert the boron atom into a wide variety of other substituents and the overall process promises to be a versatile approach for the manufacture of complex compounds and advanced materials of value to society. In combination with method development, the funded research encompasses detailed mechanistic studies designed to elucidate how the catalyst pair functions with the goals of advancing fundamental knowledge of transition metal-based catalysis and improving the efficiency and sustainability of chemical synthesis. The broader impacts of the funded project extend to the benefits accrued to society as Dr. Hull and her coworkers engage in an extensive range of educational and outreach activities, including: the ChemBridge program to improve the college readiness of young Texans who belong to groups underserved in STEM (science, technology, engineering and mathematics) fields, and ongoing efforts to propagate shared values of diversity, equity, and inclusivity among the faculty and students of UT-Austin.The funded research focuses on investigations of a recently discovered Pd/Fe-cocatalyzed aminoboration of alkenes and it features further development of the process (e.g., to expand both the substrate and nucleophile scope) and associated mechanistic studies to gain insights for the underlying role of the iron(II) triflate cocatalyst. Specifically, during the course of methodological development (Aim 1), reaction conditions for the successful aminoboration of norbornene [key reagents: PhthNH, B2Pin2, cat. Pd(MeCN)2Cl2, cat. Fe(OTf)2, and O2] will be further explored and extended to more challenging olefin substrates for which beta-hydride elimination following the Markovnikov addition stage of the process could be encountered. Nucleophiles other than N-based systems, such as O-based (e.g., phenols), S-based (e.g., thiols), and C-based (e.g., indoles), will also be investigated as will alternative transmetalation reagents (e.g., Si- and Sn-based) to potentially arrive upon a highly generalized nucleometallation process. In further efforts to broaden the versatility of the platform yet further, a remote nucleoboration transformation that incorporates a 'Pd-walking' stage (i.e., regioisomerization) prior to transmetalation is also being pursued. In mechanistic studies (Aim 2), the origin of the critical role for iron species in the transmetalation step of aminoboration is being explored as is its equally curious beneficial effect on the aza-Wacker process. Finally, in an effort to develop a more sustainable variant of the nucleoboration process (Aim 3), a heterogenous and recyclable Pd/Fe catalyst system is under development. All told, the studies being pursued are anticipated to extend the versatility of olefin difunctionalization chemistry and in so doing, facilitate the synthesis of important classes of nitrogen (and other heteroatom) containing compounds that are prominent among active pharmaceutical ingredients and other kinds of complex molecules of utility in science, engineering, and medicine.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.