Pushing the Boundaries of Pnictogen‐Bonding Organocatalysis: A Clash of Sb(III) versus Bi(III)

Tri-aryl-substituted bismuth(III) complexes exhibit superior anion (Cl⁻) binding affinity and perform as a better organocatalysts as compared to their antimony analogues. Additionally, the impact of increasing fluoride substitutions on the aryl groups is explored, with a focus on how these substitutions affect the electronic structure of these organocatalysts, strength of the σ-holes, Cl⁻ binding, and the reaction barrier.

The σ-hole-mediated noncovalent organocatalysis involving the pnictogen (Pn) elements has thus far been explored mostly from nitrogen to antimony, with antimony identified as the most effective catalyst. Herein, density functional theory calculations have been carried out to demonstrate that tri-aryl (Ar)-substituted bismuth(III) complexes can outperform their antimony counterparts in both anion (Cl⁻) binding and catalytic activity. Using a range of computational methods, a good correlation between the σ-hole strength, chloride binding affinity, and the reaction barrier is established. Notably, the findings reveal that dispersion interactions are the dominant force in catalysts with weaker σ-holes, while electrostatic interactions prevail in catalysts with stronger σ-holes (for the anion abstraction step). In all cases, Bi(III) catalysts emerge as the winner over the Sb(III) analogues. Additionally, beyond the primary Pn…Cl interactions, several secondary interactions such as Cl…H/FC(Ar) and Cl⁻…HC(Si-TBS) also play a significant role in stabilizing the transition states.

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