Taming the Lewis Superacidity of Non‐Planar Boranes: C−H Bond Activation and Non‐Classical Binding Modes at Boron

Abstract

The rational design of a geometrically constrained boron Lewis superacid featuring exceptional structure and reactivity is disclosed. It enabled the formation of non-classical electron deficient BÀHÀB type of bonding, which was supported by spectroscopic and structural parameters as well as computational studies. Taming the pyramidal Lewis acid electrophilicity through weak coordinating anion dissociation enabled a series of highly challenging chemical transformations, such as Csp 2 ÀH and Csp 3 ÀH activation under a frustrated Lewis pair regime and the cleavage of Csp 3 ÀSi bonds. The demonstration of such rich chemical behaviour and flexibility on a single molecular compound makes it a unique mediator of chemical transformations generally restricted to transition metals.

Borane-catalyzed dehydrogenative C–C bond formation of indoles with N-tosylhydrazones: an experimental and computational study

“…Over the last decade, metal-free main group catalysis has gained significant attention to unravel new reactivity and selectivity over the classical transition-metal catalysis. [39][40][41][42][43][44][45] To date a series of boron based Lewis acid catalysts have been known in the main group chemistry, out of which tris( pentafluorophenyl)borane (B(C 6 F 5 ) 3 ) has evolved as the most versatile catalyst. [46][47][48] The inherent electrophilic character and strong Lewis acidity have increased its applications in various transformations including cyclization, 49-53 dehydrogenation, [54][55][56][57] hydrosilylation, [58][59][60][61] hydroboration, 62,63 and Frustrated Lewis Pair (FLP) chemistry [64][65][66][67][68] for activation of small molecules.…”

The Effect of Carborane Substituents on the Lewis Acidity of Boranes

“…From these calculations, the substituent effects on the Lewis acidity follow the trend ofBerionni and coworkers have been leveraging constrained geometry at the boron center to generate extremely Lewis acidic boranes in situ, but the free Lewis acids have yet to be isolated. [46][47][48] Dicarbadodecaboranes, or carboranes, are C2B10H12 icosahedral clusters composed of boron, carbon, and hydrogen atoms that are bonded non-classically. 49 The three isomers of neutral C2B10H12 are named based on the relative positions of the two carbon atoms in the icosahedron: ortho (carbon atoms adjacent, 1-and 2-positions), meta (carbon atoms separated by a boron atom, 1-and 7-positions), and para (carbon atoms separated by two boron atoms on opposite sides of the cage, 1-and 12-positions).…”