HIGHLY ELECTROPHILIC NITRENIUM RADICALS

影响：在英国制造业中，化学品生产占340亿GB。高达90%的化工产品在制备过程中需要使用催化剂。[1]这些催化剂通常是以贵金属为基础的，包括钯、铂和铑。过度开采这些不可再生资源加剧了与其使用相关的环境和地缘政治问题以及成本。[2]开发基于地球上丰富的主要组元素的替代品，包括氮，日益紧迫，并引起了全球的关注。背景：受挫的路易斯对(FLP)是主族催化剂中最成功的例子之一。[3]FLP的特点是具有Lewis碱性和Lewis酸性中心，它们协同工作以模拟过渡金属的前线轨道。使它们能够激活广泛的小分子，并促进关键的有机转化。然而，碳-碳键的形成催化仍然是一个挑战。开发能够氧化还原循环的新型自由基FLP将解锁与主要基团元素的前所未有的催化作用，例如氧化还原C-C键形成反应。到目前为止，氮基化合物一直被用作Flp的Lewis碱性组分，而不是Lewis酸性组分。目的：发展硝阳离子作为自由基FLP化学的组成部分。EPSRC的任务：开发更可持续和环境友好的工艺，符合EPSRC的投资和支持的研究领域：制造未来、物理科学和催化；以及重大挑战‘拨号分子-100%有效的合成’。研究问题和方法：氮正离子是一种新的氮基Lewis酸家族，其反应活性在很大程度上仍未被探索。我们首次发现这些阳离子在有机催化中的应用，并发现它们对水分表现出显著的稳定性。[4]自从本文提交以来，我们还发现，氮离子可以稳定自由基，这些自由基可以随后被光激发，使它们成为自由基FLP化学中的高度还原伙伴，促进新键的形成反应。该项目涉及三个工作包(WPS)。WP1(铅：MM)：氮阳离子的合成将以两类硝离子为目标，它们是基于已知的稳定自由基的萘主链的那些。以及那些基于苯基主链装饰有吸电子基团的化合物，如卤素，它增加了硝离子的路易斯酸度和亲电性。WP2(Lead：AB)：对氮离子的EPR研究。将对WP1中的氮离子进行循环伏安测试，以确定还原时形成的最稳定的自由基。接下来，我们将用化学计量比的还原剂来生成硝基，并通过EPR实验来确定这些自由基的化学和电子结构。[5]WP3(铅MM)：在催化中的应用将用UV-Vis光谱研究WP1中形成的与其Lewis碱FLP对应的硝阳离子，以确定它们在光催化中的适用性。一旦硝基的性质被量化为sigma型或pi型(来自WP2)，并确定了合适的光/电催化条件，它们将在新的成键反应中进行测试。将确定所有催化转化的底物范围和催化效率。[Q.-L.周，Angew.化学。内部艾德。2016，55,5352。[2]首页--期刊主要分类--期刊细介绍--期刊题录与文摘--期刊详细文摘内容化学。2019年、6月、2095年。[3]M.Mehta，C.B.Caputo，《竞争过渡金属反应性--受挫Lewis对化学的探索》，合成无机化学(2021)。[4]M.Mehta，J.M.Goicoechea，Angew.化学。内部艾德。2020年，59,2715。[5]首页--期刊主要分类--期刊细介绍--期刊题录与文摘--期刊详细文摘内容欧元。J.2020，26,8871.

Impact: Chemical production accounts for £34 billion within the UK manufacturing sector. Up to 90% of chemical products require the use of a catalyst at some point in their preparation.[1] Often these catalysts are based on expensive precious metals including palladium, platinum, and rhodium. Excessive mining of these non-renewable resources has exacerbated environmental and geopolitical issues associated with their use, as well as costs.[2] Developing alternatives based on earth abundant main group elements including nitrogen is increasingly urgent and has garnered global attention. Background: Frustrated Lewis Pairs (FLPs) are amongst the most successful examples of main group catalysts.[3] FLPs feature a Lewis basic and Lewis acidic site that work cooperatively to mimic the frontier orbitals of transition-metals. Allowing them to activate a wide range of small molecules and facilitate key organic transformations. However, carbon-carbon bond formation catalysis still remains a challenge. Developing new radical FLPs that can redox cycle will unlock unprecedented catalysis with main group elements, such as redox C-C bond formation reactions. Thus far, nitrogen-based compounds have been used as the Lewis basic component of FLPs, not as the Lewis acidic component. Objective: Develop nitrenium cations as components in radical FLP chemistry.EPSRC Remit: Developing more sustainable and environment-friendly processes aligns with the EPSRC research areas of investment and support: manufacturing the future, physical sciences, and catalysis; and to the grand challenges 'dial-a-molecule - 100% efficient synthesis'.Research Question and Approach: Nitrenium cations are a new family of nitrogen-based Lewis acids, the reactivity of which remains largely unexplored. We found the first application of these cations in organic catalysis, and found that they exhibited remarkable stability towards moisture. [4] Since this submission, we have also found that nitrenium cations can stabilize radicals which can be subsequently photoexcited, making them highly reducing partners in radical FLP chemistry to promote new-bond forming reactions. The project involves three work packages (WPs). WP1 (Lead: MM): Synthesis of Nitrenium Cations Two categories of nitrenium cations will be targeted, those based on a naphthalene backbone which is known to stabilize radicals. And those based on a phenyl backbone decorated with electron-withdrawing groups, such as halogens, which increases the Lewis acidity and electrophiles of the nitrenium cation. WP2 (Lead: AB): EPR Studies into Nitrenium Cations. Cyclic voltammetry on the nitrenium cations from WP1 will be undertaken to determine which form the most stable radical upon reduction. Next, nitrenium radicals will be made with stoichiometric reductants and studied with EPR experiments to define the chemical and electronic structure of these radicals.[5] WP3 (Lead MM): Application in Catalysis The nitrenium cations developed in WP1 with their Lewis base FLP counterpart will be studied by UV-vis spectroscopy to determine their suitability in photocatalysis. Once the nature of the nitrenium radical has been quantified as either sigma- or pi-type (from WP2), and suitable photo/electro-catalytic conditions determined, they will be tested in new bond formation reactions. Substrate scope and catalytic efficiency will be established for all catalytic transformations. 1] Q.-L. Zhou, Angew. Chem. Int. Ed. 2016, 55, 5352. [2] O. Berger, K. R. Winters, A. Sabourin, S. V. Dzyuba, J.-L. Montchamp, Org. Chem. Front 2019, 6, 2095. [3] M. Mehta, C. B. Caputo, Rivaling transition metal reactivity - an exploration of frustrated Lewis pairs chemistry, Synthetic Inorganic Chemistry (2021). [4] M. Mehta, J. M. Goicoechea, Angew. Chem. Int. Ed. 2020, 59, 2715. [5] A. Kutt, G. Jeschke, L. Toom, J. Nerut, C. A. Reed, Chem. Eur. J. 2020, 26, 8871.