Johannes H. J. Berthel

Preparing (Multi)Fluoroarenes as Building Blocks for Synthesis: Nickel-Catalyzed Borylation of Polyfluoroarenes via C–F Bond Cleavage

The [Ni(IMes)2]-catalyzed transformation of fluoroarenes into arylboronic acid pinacol esters via C-F bond activation and transmetalation with bis(pinacolato)diboron (B2pin2) is reported. Various partially fluorinated arenes with different degrees of fluorination were converted into their corresponding boronate esters.

Intramolecular CN Bond Activation and Ring-Expansion Reactions of N-Heterocyclic Carbenes

Intramolecular ring-expansion reactions (RER) of the N-heterocyclic carbene 1,3-dimethylimidazolin-2-ylidene were observed upon vacuum ultraviolet (VUV) photoexcitation. Similarly to RERs reported in the solvent phase, for the reaction of NHCs with main-group-element hydrides, hydrogen transfer to the NHC carbon atom is the crucial initial step. In an ionization-mediated protonation, 1,3-dimethylimidazolin-2-ylidene forms an imidazolium ion, which is the rate-limiting step on the pathway to two six-membered ring products, namely, methylpyrimidinium and -pyrazinium ions. To unravel the reaction path, we have used imaging photoelectron photoion coincidence spectroscopy with VUV synchrotron radiation, as well as high-level composite method calculations. Similarities and differences between the mechanism in the gas phase and in the condensed phase are discussed.

NHC Nickel-Catalyzed Suzuki–Miyaura Cross-Coupling Reactions of Aryl Boronate Esters with Perfluorobenzenes

An efficient Suzuki-Miyaura cross-coupling reaction of perfluorinated arenes with aryl boronate esters using NHC nickel complexes as catalysts is described. The efficiencies of different boronate esters (p-tolyl-Beg, p-tolyl-Bneop, p-tolyl-Bpin, p-tolyl-Bcat) and the corresponding boronic acid (p-tolyl-B(OH)2) in this type of cross-coupling reaction were evaluated (eg, ethyleneglycolato; neop, neopentylglycolato; pin, pinacolato; cat, catecholato). Aryl-Beg was shown to be the most reactive boronate ester among those studied. The use of CsF as an additive is essential for an efficient reaction of hexafluorobenzene with aryl neopentylglycolboronates.

CCDC 1529577: Experimental Crystal Structure Determination

Related Article: Martin Eck, Sabrina Wurtemberger-Pietsch, Antonius Eichhorn, Johannes H. J. Berthel, Rudiger Bertermann, Ursula S. D. Paul, Heidi Schneider, Alexandra Friedrich, Christian Kleeberg, Udo Radius, Todd B. Marder|2017|Dalton Trans.|46|3661|doi:10.1039/C7DT00334J