Characterization of the Zwitterionic Intermediate in 1, 1‐Carboboration of Alkynes. (29th May 2020)

• Record Type: Journal Article
• Authors: Bismuto, Alessandro; Nichol, Gary S.; Duarte, Fernanda; Cowley, Michael J.; Thomas, Stephen P.
• Is Part Of: Angewandte Chemie. Volume 132:Number 31(2020)
• Page Start: 12831
• Page End: 12835
• Publication Date: 2020-05-29
• Subjects: 1, 1-carboboration -- frustrated Lewis pairs -- reaction mechanisms -- vinyl cation; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202003468
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1, 1‐carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1, 1‐Carboboration has been proposed to proceed through a zwitterionic intermediate. We report the isolation and spectroscopic, structural and computational characterization of the zwitterionic intermediates generated by reaction of B(C6 F5 )3 with alkynes. The stepwise reactivity of the zwitterion provides new mechanistic insight for 1, 1‐carboboration and wider B(C6 F5 )3 catalysis. Making use of intramolecular stabilization by a ferrocene substituent, we have characterized the zwitterionic intermediate in the solid state and diverted reactivity towards alkyne cyclotrimerization. Abstract : The isolation and characterization of the zwitterionic intermediate in 1, 1‐carboboration reactions is reported. The highly reactive zwitterionic intermediates are generated from tris(pentafluorophenyl)borane and alkynes under reaction conditions of 1, 1‐carboboration.