Over‐Oxidation as the Key Step in the Mechanism of the MoCl5‐Mediated Dehydrogenative Coupling of Arenes |
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| Authors: | Moritz Schubert Peter Franzmann Dr Anica Wünsche?von?Leupoldt Prof?Dr Konrad Koszinowski Prof?Dr Katja Heinze Prof?Dr Siegfried R Waldvogel |
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| Institution: | 1. Department of Organic Chemistry, Johannes Gutenberg University Mainz, Mainz, Germany;2. Department of Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10–14, Mainz, Germany;3. Institute of Organic and Biomolecular Chemistry, Georg-August-Universit?t G?ttingen, G?ttingen, Germany |
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| Abstract: | Molybdenum pentachloride is an unusually powerful reagent for the dehydrogenative coupling of arenes. Owing to the high reaction rate using MoCl5, several labile moieties are tolerated in this transformation. The mechanistic course of the reaction was controversially discussed although indications for a single electron transfer as the initial step were found recently. Herein, based on a combined study including synthetic investigations, electrochemical measurements, EPR spectroscopy, DFT calculations, and mass spectrometry, we deduct a highly consistent mechanistic scenario: MoCl5 acts as a one‐electron oxidant in the absence of TiCl4 and as two‐electron oxidant in the presence of TiCl4, but leads to an over‐oxidized intermediate in both cases, which protects it from side reactions. In the course of aqueous work‐up the reagent waste (MoIII/IV species) acts as reducing agent generating the desired organic C?C coupling product. |
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| Keywords: | arene coupling C− C coupling cyclization molybdenum oxidative coupling |
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