title: Elucidating the Reactivity of Vicinal Dicarbenoids: From Lewis Adduct Formation to B-C Bond Activation.
abstract: The reactivity of the diaminoacetylene Pip-C≡C-Pip (Pip=piperidyl=NC5H10) towards phenyldichloro- and triphenylborane is presented. In the case of the less Lewis acidic PhBCl2, the first example of a double Lewis adduct of a vicinal dicarbenoid is reported. For the more Lewis acidic triphenylborane, coordination to the bifunctional carbene leads to a mild B-C bond activation, resulting in a syn-1,2-carboboration. Ensuing cis/trans isomerization yields a novel ethylene-bridged frustrated Lewis pair (FLP). The compounds were characterized using multinuclear NMR spectroscopy, structural analysis, and mass spectrometry. Reactivity studies of both isomers with the N-heterocyclic carbene 1,3-dimethylimidazol-2-ylidene (IMe) aided in elucidating the proposed isomerization pathway. DFT calculations were carried out to elucidate the reaction mechanism. The rather low free energy of activation is consistent with the observation that the reaction proceeds smoothly at room temperature.
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Hauke
authors.initials: H
authors.lastname: Kelch
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Kachel
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Mehmet Ali
authors.initials: MA
authors.lastname: Celik
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Marius
authors.initials: M
authors.lastname: Schäfer
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Wennemann
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Radacki
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany.
authors.forename: Alex R
authors.initials: AR
authors.lastname: Petrov
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106, Braunschweig, Germany. m.tamm@tu-bs.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Tamm
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074, Würzburg, Germany. h.braunschweig@uni-wuerzburg.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Braunschweig
keywords: bond activation; carboboration; diaminoacetylene; dicarbenoid; frustrated Lewis pairs