On the Bonding in Bis-pyridine Iodonium Cations*

A study on the bonding in bis-pyridine halonium cations has been carried out using both theoretical and synthetic techniques. The primary thrust for the study is to highlight the opportunities potentially afforded by considering iodine as a Lewis acid in a classic coordination sense. Our results suggest that the iodine dipyridine complex ([pyr-I-pyr]+) can be considered as a coordination complex of [I]+. The lighter bromine and chlorine analogues are more towards the covalent rather than the dative side of bonding, while [pyr-F-pyr]+ is best described as an ion-molecule complex with one strong covalent F-pyr bond and one weak F-pyr dispersion interaction. Finally, theoretical and synthetic studies suggest that the commercially available [pyr-F]+ cation cannot be considered as a coordination complex of ‘F+’, despite its use as a source of electrophilic fluorine.