title: Over-Oxidation as the Key Step in the Mechanism of the MoCl5-Mediated Dehydrogenative Coupling of Arenes.
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 (Mo(III/IV) species) acts as reducing agent generating the desired organic C-C coupling product.
authors.affiliation: Department of Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128, Mainz, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Schubert
authors.affiliation: Department of Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128, Mainz, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Franzmann
authors.affiliation: Department of Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128, Mainz, Germany.
authors.forename: Anica
authors.initials: A
authors.lastname: Wünsche von Leupoldt
authors.affiliation: Institute of Organic and Biomolecular Chemistry, Georg-August-Universität Göttingen, Tammannstrasse 2, 37077, Göttingen, Germany. konrad.koszinowski@chemie.uni-goettingen.de.
authors.forename: Konrad
authors.initials: K
authors.lastname: Koszinowski
authors.affiliation: Department of Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128, Mainz, Germany. katja.heinze@uni-mainz.de.
authors.forename: Katja
authors.initials: K
authors.lastname: Heinze
authors.affiliation: Department of Organic Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128, Mainz, Germany. waldvogel@uni-mainz.de.
authors.forename: Siegfried R
authors.initials: SR
authors.lastname: Waldvogel
keywords: C−C coupling; arene coupling; cyclization; molybdenum; oxidative coupling