A Stable but Highly Reactive Phosphine-Coordinated Borenium: Metal-free Dihydrogen Activation and Alkyne 1,2-Carboboration

• Published in: Angewandte Chemie International Edition Vol. 54; no. 19; pp. 5722 - 5726
• Main Authors: Devillard, Marc, Brousses, Rémy, Miqueu, Karinne, Bouhadir, Ghenwa, Bourissou, Didier
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 04.05.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Edition: International ed. in English
• Subjects: Alkynes; Bonding; Boranes; borenium cations; Bridges (structures); Cationic; Cations; Chemical Sciences; Chemistry; Chemistry, Multidisciplinary; Cleavage; density functional calculations; frustrated Lewis pairs; H2 activation; Mathematical analysis; phosphorus; Physical Sciences; Science & Technology; Splitting; density functional calculations; HYDROGEN; ROUTE; H-2 activation; COMPLEX; borenium cations; BORANES; MAIN-GROUP ELEMENTS; frustrated Lewis pairs; phosphorus; CATIONS; HYDRIDE; H2 activation
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201500959

Borenium cations have been found to be valuable analogues of boranes as a result of their cationic character which imparts high electrophilicity. Herein, we report the synthesis, characterization, and reactivity of a new type of borenium cation employing a naphthyl bridge and a strong intramolecular P→B interaction. The cation reacts with H2 in the presence of PtBu3 (frustrated Lewis pair (FLP) approach) but also on its own. The mechanism of the reaction between the borenium cation and H2 in the absence of PtBu3 has been investigated using deuterium‐labeling experiments and DFT calculations. Both experiments and calculations imply the side‐on coordination of H2 to the B center, followed by heterolytic splitting and BC bond cleavage. An uncommon syn 1,2‐carboboration has also been observed upon reaction of the borenium ion with 3‐hexyne. Versatile reactivity: A new type of borenium cation is reported in which a naphthyl bridge supports a strong P→B interaction. Borenium reacts with H2 through side‐on coordination of H2 to boron, heterolytic splitting, and concomitant cleavage of the BMes bond. The molecule also reacts with 3‐hexyne through a syn 1,2‐carboboration reaction. NTf2−=triflimide.