From Proton to Boron: The Lewis Analogs of Protonated Brønsted Super Acids.

Isolation and characterization of highly reactive intermediates are crucial to understand the nature of chemical reactivity. Accordingly, the reactivity of weakly coordinating anions (WCA), usually used to stabilized cationic super electrophiles are of fundamental interest. When a variety of WCA are known to form stable σ-complexes with a proton, inducing Brønsted super acidity, bis-coordinated weak-coordinated anions are much more elusive and considered as long-sought reactive species.

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

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 B-H-B 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 -H and Csp -H activation under a frustrated Lewis pair regime and the cleavage of Csp -Si bonds.

Methylene Bridging Effect on the Structures, Lewis Acidities and Optical Properties of Semi-planar Triarylboranes.

Three synthetic methods towards semi-planar triarylboranes with two aryl rings connected by a methylene bridge have been developed. The fine-tuning of their stereoelectronic properties and Lewis acidities was achieved by introducing fluorine, methyl, methoxy, n-butyl and phenyl groups either at their exocyclic or bridged aryl rings. X-ray diffraction analysis and quantum-chemical calculations provided quantitative information on the structural distortion experienced by the near planar hydro-boraanthracene skeleton during the association with Lewis bases such as NH and F .

Controlled Generation of 9-Boratriptycene by Lewis Adduct Dissociation: Accessing a Non-Planar Triarylborane.

A highly bent triarylborane, 9-boratriptycene, was generated in solution by selective protodeboronation of the corresponding tetra-aryl boron ate complex with the strong Brønsted acid HNTf . The iptycene core confers enhanced Lewis acidity to 9-boratriptycene, making it unique in terms of structure and reactivity. We studied the stereoelectronic properties of 9-boratriptycene by quantifying its association with small N- and O-centered Lewis bases, as well as with sterically hindered phosphines.

Pushing the Lewis Acidity Boundaries of Boron Compounds With Non-Planar Triarylboranes Derived from Triptycenes.

Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to a series of 9-boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopy and X-ray diffraction of the Lewis adducts of these non-planar boron Lewis acids with weak Lewis base revealed particularly strong covalent bond formation. The first Lewis adduct of a trivalent boron compounds with the Tf N anion illustrates the unrivaled Lewis acidity of these species.