Control experiments offered additional evidence against the notion that 1 functions as a halogen bond generating catalyst. We investigated the capacity of 10 mol% of pentafluoroiodobenzene, a superior halogen bond donor to 1, to facilitate the efficient synthesis of racemic cisaziridine (Scheme 1a). If aziridine formation was catalysed by a halogen bond, one would expect similar or even improved catalytic performance with pentafluoroiodobenzene ; however, neither any aziridine nor indeed a reaction was observed (Scheme 1b). Whereas the same reaction with 10 mol% of 1 afforded racemic cisaziridine in an unoptimised 68% yield after only 10 minutes (Scheme 1b). This crucial observation negates the longstanding assumption that 1 is functioning via a 'classic' halogen bond. We also explored whether 1 was able to catalyse aziridine synthesis via hydrogen bonding or π-π interactions . Interestingly, in both cases, the DFT calculations indicate 1 is unable to catalyse the synthesis of aziridine either via hydrogen bonds or π-π interactions (see Figure in SI).