Bulky iodotriazolium tetrafluoroborates as highly active halogen-bonding-donor catalysts

Steric bulk around catalytic centers is one of the most important factors determining catalytic reactivities and selectivities. This paper reports the synthesis of structurally diverse 5-iodo-3-methyl-1,2,3-triazolium salts and the evaluation of their catalytic activities as halogen-bonding donors for the aza-Diels-Alder reaction of 2-siloxy-1,3-butadiene with imines. We found that steric hindrance around an iodide atom in halogen-bonding donors significantly impacted catalytic efficiency.