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

As part of our investigations into the Lewis acidic behavior of antimony derivatives, we have decided to study the properties of 5-phenyl-5,5-dichloro-lambda 5-dibenzostibole (1), a dichlorostiborane with an antimony atom confined to a five-membered heterocycle. Our work shows that the resulting geometrical constraints elevate the Lewis acidity of the antimony atom, as confirmed by the crystal structure of 1-THF and the solution study of the interaction of 1 with Ph3PO. The enhanced Lewis acidic properties of 1, which exceed those of simple dichlorostiboranes such as Ph3SbCl2, also become manifest in pnictogen bonding catalysis experiments involving the reductions of imines with Hantzsch ester. The influence of geometrical constraints in the chemistry of this compound is also supported by a computational activation strain analysis as well as by an energy decomposition analysis of a model Me3PO adduct.

Automated summary

As part of our investigations into the Lewis acidic behavior of antimony derivatives, we studied the properties of 5-phenyl-5,5-dichloro-lambda 5-dibenzostibole (1), a dichlorostiborane with an antimony atom confined to a five-membered heterocycle. Our work confirmed that the geometric constraints of this compound enhance the Lewis acidity of the antimony atom, as evidenced by crystal structure analysis and solution studies. The compound's enhanced Lewis acidic properties were also observed in pnictogen bonding catalysis experiments involving imine reductions.