Direct π‐Activation vs. <i>O</i> ‐Activation in Halogen‐Bonding Catalysis

Halogen bond donors had an increasing impact on catalysis in recent years, and their development is highly active. In particular, numerous iodine-based halogen have been developed used to promote various reactions through coordinating carbonyl groups, a ubiquitous mode of activation catalysis. We now report computational data which strongly suggests that alternative mode, direct π-complexation, operative for unsaturated substrates. Calculations also suggest solvent polarity could clear the preference activation, raising possibility mechanistic manifold switch variation. These findings profoundly next generation halogen-bond donor catalysts.