Electrochemistry of Hypervalent Halogen Compounds

• Applicant: Professor Dr. Robert Francke
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326232685

Due to their versatility and efficiency, hypervalent iodine compounds represent an important class of reagents in organic synthesis. However, separation from the reaction mixture is usually problematic and application on the technical scale has not yet been established due to high costs and safety issues. These points were taken into account by project (sign removed), which aimed at developing efficient and resource-saving methods for the in-situ generation of iodine(III) species. The electrochemical generation of new representatives of this compound class was investigated and their use as mediators in organic transformations was tested. By tethering the aryl iodide unit to ionic groups, the separation from the product mixture was facilitated and thus recyclability was ensured. Simultaneously, the use of supporting electrolyte additives was rendered obsolete, which greatly simplified the separation of the product mixture. In addition to the correlation between mediator structure and electrochemical properties, new applications were developed in the fields of oxidative coupling, cyclization reactions and rearrangements.Based on the findings obtained during the work on project (sign removed), a further exploration of the electrochemistry of hypervalent halogen compounds is planned. First of all, the developed concept will be transferred to hypervalent bromine compounds. Despite their interesting properties, the latter have so far been little described, which can be ascribed to their high reactivity and the problematic synthesis starting from the difficult-to-handle bromine trifluoride. Therefore, we plan the electrochemical conversion of aryl bromides to the corresponding bromanes and to subsequently test their suitability as mediators for different transformations.A further important aspect of the project is the development of an electrocatalytic in-cell process in which the aryl halide is only used in sub-stoichiometric quantities. This was previously not possible due to the high oxidation potential of the mediators, which is why the stoichiometric ex-cell method had to be used. For the realization of electrocatalytic processes, several mediator structures and suitable applications are proposed in the project description.The electrochemical synthesis of organic iodine (V) compounds is another goal of the planned project. Despite their versatile application as oxidizing agents, electrochemical syntheses of representatives of this compound class have not yet been described. Here, too, the advantage of electrochemical in-situ generation is obvious due to the risks involved in handling iodine(V) reagents. To achieve this goal, several iodoarene structures with ortho-stabilizing substituents are proposed.

• DFG Programme: Research Grants