A Selenenium-Bridged 10-Boratriptycene Lewis Acid

Abstract

A non-planar triarylborane and a new member of the boratriptycene family bearing a selenium atom in bridgehead position of triptycene scaffold was generated and isolated as a boron-“ate” complex paired with a weakly coordinating anion. With similar electronegativity while possessing longer atom radius with respect to sulfur, the introduction a selenium atom, under the form of a selenenium moiety at the bridgehead of a triptycene scaffold allows a very precise modification of the pyramidalization of the boron atom environment. Experimental and computational evaluation of the Lewis acidity of this new boratriptycene derivative gave qualitative information on how a modification of the pyramidalization of the boron environment affects alone Lewis acidity parameters of such pyramidal triarylborane.

Ligand-enforced geometric constraints and associated reactivity in p-block compounds

“…The analogous base-stabilized cationic 9-bora-thiotriptycene and 9-bora-selenotriptycenes have also been reported recently (6S-L and 6Se-L). 53,54 The larger backbone atom in these cages allows for slight structural relaxation reducing the degree of pyramidalization at boron. Nevertheless, such cations exhibit very high Lewis acidity, which was harnessed for challenging C-H activations as well as a very rare case of C(sp 3 )-Si bond cleavage.…”

Synthesis, bridgehead functionalization, and photoisomerization of 9,10-diboratatriptycene dianions

“…1) possessing various different atoms/groups "E" at the second bridgehead position (E = CH, PH + , S + , Se + ). [17][18][19][20] A derivative of C combining E = CH and Ar = 4-t-Bu-C 6 H 4 underwent selective protodeboronation of the exocyclic C-B bond upon treatment with bistriimidic acid (HNTf 2 ); the resulting boratriptycene Lewis acid still engages in a dynamic association-dissociation equilibrium with the weakly coordinating [NTf 2 ] − anion. 18 This nding underscores the potential for enhancing Lewis acidity by designing a rigid organic framework in a way to impose a structural constraint on the BC 3 core that forces it out of planarity (see also the Lewis superacidity of [B − H] + mentioned above 16 ).…”

Are Ar3SbCl2 Species Lewis Acidic? Exploration of the Concept and Pnictogen Bond Catalysis Using a Geometrically Constrained Example

“…In the context of Lewis acid chemistry, it has long been known that simply incorporating silicon into a rigid five-membered structure elevates its Lewis acidity . Similar strategies have been employed in the chemistry of group 13 compounds as in the case of distorted or pyramidalyzed boranes, with externally exposed “vacant” oribtals . The same concepts have driven a surge of efforts in pnictogen chemistry, where ligand-imposed geometrical constraints have been used to adjust not only the Lewis acidity of the main group element but also its redox reactivity .…”

“… 1 Similar strategies have been employed in the chemistry of group 13 compounds as in the case of distorted or pyramidalyzed boranes, with externally exposed “vacant” oribtals. 2 The same concepts have driven a surge of efforts in pnictogen chemistry, where ligand-imposed geometrical constraints have been used to adjust not only the Lewis acidity of the main group element but also its redox reactivity. 3 Examples of such compounds include bicyclic phosphonium cations such as A ( 4 ) and B , 5 which display remarkable, group 15-centered Lewis acidity ( Chart 1 ).…”