Boron-Centered Lewis Superacid through Redox-Active Ligands: Application in C−F and S−F Bond Activation

A series of redox-responsive ferrocenyl-substituted boranes and boronic esters were synthesized. Oxidation of the ferrocenyl ligand to the ferrocenium resulted in a drastic increase in the Lewis acidity beyond the strength of SbF₅, which was investigated experimentally and computationally. The resulting highly Lewis acidic boron compounds were used for catalytic C−F and S−F bond activation.     

A Water- and Base-Stable Iminopyridine-Based Cage That Can Bind Larger Organic Anions

Catalysis inside molecular cages and capsules has attracted an increasing amount of attention over the last decade. While many examples of the catalysis of reactions with cationic intermediates and transition states are known, those with anionic counterparts are scarce. One limiting factor is access to suitably sized cationic iminopyridine-based cages that are stable towards water and anionic/nucleophilic guest molecules. This study aimed at identifying such suitable cages. In this full paper, we describe the journey that finally led to the synthesis of a novel iminopyridine-based tetrahedron that can bind larger organic anions with binding constants of up to 850 M⁻¹ in MeCN−d₃/H₂O=9 : 1. Importantly, it also displays stability in basic aqueous acetonitrile. Surprisingly, investigations towards catalysis of reactions with anionic transition states did not indicate rate accelerations in the presence of the cage.