HIGHLY ELECTROPHILIC NITRENIUM RADICALS

影响：化学品生产在英国制造业中占340亿英镑。高达90%的化学产品在制备过程中需要使用催化剂。[1]这些催化剂通常基于昂贵的贵金属，包括钯、铂和铑。对这些不可再生资源的过度开采加剧了与其使用有关的环境和地缘政治问题以及成本。[2]开发基于地球丰富的主族元素（包括氮）的替代品日益紧迫，并已引起全球关注。背景：阻挫刘易斯对（FLP）是主族催化剂中最成功的例子。[3]FLP具有刘易斯碱性和刘易斯酸性位点，其协同工作以模拟过渡金属的前线轨道。使它们能够激活各种小分子，促进关键的有机转化。然而，碳-碳键形成催化仍然是一个挑战。开发可以氧化还原循环的新自由基FLP将开启前所未有的主族元素催化作用，例如氧化还原C-C键形成反应。迄今为止，氮基化合物已被用作FLP的刘易斯碱性组分，而不是用作刘易斯酸性组分。目的：开发氮阳离子作为自由基FLP化学的组分。EPSRC Remit：开发更可持续和环境友好的工艺与EPSRC的投资和支持研究领域保持一致：制造未来，物理科学和催化;以及迎接“拨号分子-100%高效合成”的巨大挑战。氮鎓阳离子是一类新的氮基刘易斯酸，其反应活性在很大程度上尚未研究。我们发现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着的稳定性。[4]自该提交以来，我们还发现氮阳离子可以稳定随后可以被光激发的自由基，使它们在自由基FLP化学中成为高度还原的伙伴，以促进新键形成反应。该项目涉及三个工作包（WP）。WP 1（导联：MM）：氮鎓阳离子的合成将针对两类氮鎓阳离子，基于萘骨架的那些，已知其稳定自由基。以及那些基于苯基主链的，用吸电子基团如卤素修饰的，这增加了氮阳离子的刘易斯酸性和亲电性。WP 2（铅：AB）：氮阳离子的EPR研究。将对WP 1的氮阳离子进行循环伏安法，以确定还原后形成最稳定的自由基。接下来，氮素自由基将与化学计量还原剂和EPR实验研究，以确定这些自由基的化学和电子结构。[5]WP 3（电极导线MM）：在催化中的应用将通过紫外-可见光谱研究WP 1中开发的氮鎓阳离子及其刘易斯碱FLP对应物，以确定其在催化剂中的适用性。一旦氮鎓自由基的性质被量化为σ型或π型（来自WP 2），并且确定了合适的光/电催化条件，它们将在新的键形成反应中进行测试。将为所有催化转化确定底物范围和催化效率。1]问：L. Zhou，Angew.国际化学版2016，55，5352中所述。[2]O. Berger，K. R. Winters，A. Sabourin，S. V. Dzyuba，J.- L. Montchamp，Org. Chem. Front 2019，6，2095. [3]M.梅塔角B。Caputo，Rivaling transition metal reactivity - an exploration of frustrated刘易斯易斯pairs chemistry，Synthetic Inorganic Chemistry（2021）。[4]M. Mehta，J. M. Goicoechea，Angew.国际化学版2020，59，2715中所述。[5]A. Kutt，G.耶施克湖Toom，J. Nerut，C. A. Reed，Chem. Eur. J. 2020，26，8871中所述。

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.