Exploring Triel Bonding to Halogens for More Potent σ-Holes

Noncovalent interactions are indispensable to chemical science and crucial to fostering new perspectives on molecular structure and reactivity. In this pursuit, halogen bonding has been the object of much attention in recent years, and strategies to enhance and control this noncovalent force are highly sought. In shaping this area, we show here neutral and cationic boron centers through triel bond donor-acceptor X → B (X = Cl, Br, I) interactions allow for enhanced halogen bonding. Central to this concept is donation from the electron-rich belt of a halogen atom to an electron deficient boron center achieved by peri-proximity on a naphthyl scaffold. As shown in this study, such interactions are capable of enhancing the halogen bonding ability by more than 7 kcal/mol. To further probe this effect, experimental studies demonstrating the power of this interaction for catalysis are offered in the context of imine reduction. Overall, this experimental and computationally based study contributes to the development of fundamental aspects of organoboron chemistry and halogen bonding.