HIGHLY ELECTROPHILIC NITRENIUM RADICALS

影响：化学产品在英国制造业中占340亿英镑。高达90%的化学产品在其制备过程中的某些环节都需要使用催化剂这些催化剂通常是基于昂贵的贵金属，包括钯、铂和铑。对这些不可再生资源的过度开采加剧了与它们的使用相关的环境和地缘政治问题，以及成本问题开发以氮等地球上丰富的主族元素为基础的替代品日益迫切，已引起全球的关注。背景：受挫刘易斯对（FLPs）是主基团催化剂中最成功的例子之一FLPs具有刘易斯碱性和刘易斯酸性位点，它们协同工作以模拟过渡金属的前沿轨道。使它们能够激活大范围的小分子，促进关键的有机转化。然而，碳-碳键的催化形成仍然是一个挑战。开发能够氧化还原循环的新型自由基FLPs将开启前所未有的与主族元素的催化作用，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FLPs的刘易斯碱性组分，而不是刘易斯酸性组分。目的：探讨氮离子在FLP自由基化学中的作用。EPSRC的职责范围：开发更加可持续和环境友好的工艺与EPSRC的研究投资和支持领域一致：未来制造、物理科学和催化；以及“拨出一个分子——100%高效合成”的巨大挑战。研究问题和方法：氮离子是一种新的氮基路易斯酸，其反应性在很大程度上仍未被探索。我们发现了这些阳离子在有机催化中的首次应用，并发现它们对水分表现出显著的稳定性。自这篇论文发表以来，我们还发现氮离子可以稳定自由基，这些自由基随后可以光激发，使它们成为自由基FLP化学中高度还原的伙伴，以促进新键形成反应。该项目涉及三个工作包（wp）。两类硝基离子将被瞄准，它们是基于已知的稳定自由基的萘骨架。而那些以苯基为骨架并带有吸电子基团的化合物，比如卤素，会增加路易斯酸度和氮离子的亲电性。WP2 (Lead: AB): EPR对氮离子的研究。将对WP1的氮离子进行循环伏安法测定，以确定还原后哪种形成最稳定的自由基。接下来，我们将用化学计量还原剂制备氮自由基，并用EPR实验研究这些自由基的化学和电子结构WP3（铅MM）：在催化中的应用将通过紫外可见光谱研究在WP1中形成的氮离子及其路易斯碱FLP对应物，以确定它们在光催化中的适用性。一旦氮自由基的性质被量化为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。将为所有催化转化建立底物范围和催化效率。1) Q.-L。周,Angew。化学。Int。编辑。2016,55,5352。[10]刘建军，刘建军，刘建军，刘建军。Montchamp Org。化学。前沿，2019,6,2095。[10] M. Mehta， C. B. Caputo，过渡金属反应性的竞争-受挫Lewis对化学的探索，合成无机化学（2021）。[10] M. Mehta， J. M. Goicoechea，安格鲁。化学。Int。编辑。2020,59,2715。[10] A. Kutt， G. Jeschke， L. Toom， J. Nerut， C. A. Reed, Chem。欧元。[j] . 2020, 26(1): 71 - 71。

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.