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 HNTf2. 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. The resultant Lewis adducts exhibited unique structural, spectroscopic, and photophysical properties. Beyond the high pyramidalization of the 9‐boratriptycene scaffold and its low reorganization energy upon Lewis base coordination, quantum chemical calculations revealed that the absence of π donation from the triptycene aryl rings to the boron vacant pz orbital is one of the main reasons for its high Lewis acidity.

Proline has been widely used for various cocrystallization applications, including pharmaceutical cocrystals. Combining enantiopure and racemic flurbiprofen and proline, we discovered 18 new crystal structures. Liquid-assisted grinding proved highly efficient to explore all the variety of crystal forms. A unique combination of state-of-the-art characterization techniques, comprising variable temperature in situ X-ray diffraction and in situ ball-milling, along with other physicochemical methods and density functional theory calculations, was indispensable for identifying all the phases. Analyzing the results of in situ ball-milling, we established a stepwise mechanism for the formation of several 1:1 cocrystals via an intermediate 2:1 phase. The nature of the solvent in liquid-assisted grinding was found to significantly affect the reaction rate and, in some cases, the reaction pathway.

Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to as eries of 9-boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopyand X-raydiffraction 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 at rivalent boron compounds with the Tf 2 N À anion illustrates the unrivaled Lewis acidity of these species. Increasing the pyramidalization of the boron center and using ac ationic phosphonium linker resulted in an exceptional enhancement of Lewis acidity.I ntroduction of ap hosphorus and ab oron atom at each edge of at riptycene framework, allowed access to new bifunctional Lewis acid-base 9-phospha-10-boratriptycenes featuring promising reactivity for the activation of carbon-halogen bonds.

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.

In N-salicylideneaniline derivatives, photochromism occurs by a two-step isomerization mechanism. Photochromism has been reported to be closely related to the molecular conformation of the N-salicylideneanilines (described by the dihedral angle Φ) and to the free available space (V free ) in the crystal. In this contribution, we focus on cocrystals of isomeric Nsalicylideneaminopyridines with perfluorinated halogen bond donors as coformers. The advantage of working with isomers is that they have a similar (if not equal) molecular volume. This aspect means that the evaluation and comparison of the free available spaces within cocrystals is not affected by the differences in the molecular volumes of their constituents. Cocrystals were synthesized by a one-pot procedure, which allowed concomitant formation of covalent (imine) and noncovalent (halogen) bonds. Each cocrystal was characterized by X-ray diffraction, and its photochromism was assessed by UV−vis diffuse reflectance. Our results suggest that the Φ/V free model grossly oversimplifies the complexity of the dynamic phenomenon behind the photoisomerization of N-salicylideneanilines. For the above-mentioned reasons, careful examination of intermolecular interactions and crystals packing (localization of voids, evaluation of intermolecular interactions and stacking modes) should be taken into account and used to supplement the current proposed model based on Φ and V free .