Credit: © 2009 ACS

The use of sophisticated ligands to stabilize otherwise reactive metal centres has resulted in some very useful catalysts. Diiminopyridine (DIMPY), with its three nitrogen atoms, is one example that has been widely used for transition and some p-block metals. Until now, however, neither non-metal nor dication complexes have been made, although both would allow further and enhanced reactivities.

Paul Ragogna and colleagues1 from the University of Western Ontario have made dicationic complexes of DIMPY and the chalcogens sulfur, selenium and tellurium. Reacting the ligand with a suitable chalcogen triflate synthon gave the compounds as triflate salts in the form of yellow or amber powders. Proton NMR spectroscopy revealed that the chemical shifts of the hydrogen nuclei bonded to the α-carbon were characteristic of a dication.

The chalcogens were shown by X-ray diffraction to be in a T-shaped coordination geometry, which is distorted further away from the ideal shape with increasing chalcogen size. Further geometrical parameters suggest that the charge is delocalized throughout the dication, which Ragogna and colleagues describe as a pyridinium/iminium salt. Although the small number of previously reported dicationic chalcogen complexes were highly unstable, these DIMPY compounds were stable in open air for weeks (sulfur) and months (selenium and tellurium).