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Oxidative coupling of arenes using molybdenum(V) reagents

使用钼 (V) 试剂进行芳烃的氧化偶联

基本信息

批准号：
296012784
负责人：
Professor Dr. Siegfried R. Waldvogel
金额：
--
依托单位：
Department Elektrosynthese
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/296012784?language=en
关键词：
Oxidative coupling arenes using molybdenum

项目摘要

Dehydrogenative coupling reactions of arenes have recently experienced increasing attention. Employing MoCl5 enables these conversions in high yield. However, often chlorinated substrates or products are observed as by-products. Moreover, the reaction mechanism of this oxidative coupling is still subject of divergent discussions, wherein a radical cationic or carbenium pathway is proposed as mechanistic rationale. Within this collaborative project the following topics will be addressed : 1) the scope of substrates and accessible product classes by Mo(V) reagents will be elucidated. 2) potential radical-type intermediates of the C,C-coupling with involved Mo(V) reagents will be identified, and 3) novel Mo(V) reagents will be developed, being capable to suppress chlorination, providing access to domino sequences, and to electrochemically/electrocatalytically uses. The Mo(V)-mediated coupling will be extended to a broad scope of substrates and a variety of product classes by establishing innovative domino-oxidation pathways. The coupling of aryls in benzylic position and subsequent trapping by nucleophiles will give quick access to xanthene, thioxanthene, and acridone derivatives. Oxidative coupling of pyridine N-oxides with arenes using MoX5 followed by an in-situ deoxygenation by the co-formed Mo(IV) will result in a versatile one-pot protocol to alkaloids like beta-carbolines. Most challenging will be the cross-coupling reaction. Herein, we will control the desired pathway by coordination of an additional Lewis acid which makes the most electron rich coupling component less prone to the initial oxidation step. The concept will allow a decoupling of oxidation potential from nucleophilicity to some extent, providing a general approach to cross-coupling reactions. For an understanding of the reaction pathways, and to optimize these in a rationale and efficient way, the knowledge of the mechanism will be crucial. Consequently, the detection of potential reactive intermediates of radical nature is envisioned by ESI-MS experiments of charged tag molecules. This allows the detection of neutral radical species. These experiments will be supported by calculations of intermediates and transition states of the coupling reaction on a DFT level. To optimize both, reactivity and selectivity the development of Mo(V) reagents with less or even no chlorido ligands is essential. This section will be treated in an associated project. In addition, to the recently reported complex Mo2Cl6(hfip)4 the preparation of further MoV complexes with stable fluorinated alkoxido ligands is envisaged. If the synthesis of halide-free Mo(V) alkoxido complexes, e.g. from fluorido complexes by substitution or from Mo2(hfip)6 by oxidation, is successful, an electrochemical C,C coupling using MoV as mediator should be feasible on a long term.

芳烃的脱氢偶联反应近年来受到越来越多的关注。使用MoCl 5能够以高产率实现这些转化。然而，氯化基质或氯化产物通常是作为副产物被观察到的。此外，这种氧化偶联的反应机理仍然是分歧讨论的主题，其中提出了一个自由基阳离子或碳正离子途径作为机械原理。在该合作项目中，将讨论以下主题：1）将阐明Mo（V）试剂的底物范围和可访问的产品类别。2)将鉴定与所涉及的Mo（V）试剂的C，C-偶联的潜在自由基型中间体，以及3）将开发新的Mo（V）试剂，其能够抑制氯化，提供对多米诺序列的访问，以及电化学/电催化用途。Mo（V）介导的偶联将通过建立创新的多米诺骨牌氧化途径扩展到广泛的底物和各种产品类别。芳基在苄基位置的偶联和随后被亲核试剂捕获将快速获得氧杂蒽、噻吨和吖啶酮衍生物。使用MoX 5将吡啶N-氧化物与芳烃氧化偶联，然后通过共形成的Mo（IV）进行原位脱氧，将导致生物碱如β-咔啉的通用一锅法方案。最具挑战性的将是交叉偶联反应。在此，我们将通过配位另外的刘易斯酸来控制所需的途径，所述路易斯酸使得最富电子的偶联组分不太倾向于初始氧化步骤。这个概念将允许亲核性的氧化电位在一定程度上去耦，提供了一个通用的交叉偶联反应的方法。为了理解反应途径，并以合理和有效的方式优化这些途径，机制的知识将是至关重要的。因此，设想通过带电标签分子的ESI-MS实验检测自由基性质的潜在反应性中间体。这允许检测中性自由基物质。这些实验将得到支持的中间体和过渡态的耦合反应的DFT水平上的计算。为了优化反应性和选择性，开发具有更少或甚至没有氯基配体的Mo（V）试剂是必不可少的。本节将在一个相关项目中进行处理。此外，最近报道的配合物Mo 2Cl 6（hfip）4的进一步MoV配合物与稳定的氟化alkoxido配体的制备设想。如果无卤化物的Mo（V）烷氧基络合物的合成（例如通过取代由氟代络合物或通过氧化由Mo 2（hfip）6）是成功的，则使用MoV作为介体的电化学C，C偶联应该是长期可行的。