Chiral ferrocenyl-iodotriazoles and -iodotriazoliums as halogen bond donors. Synthesis, solid state analysis and catalytic properties.

Despite the increasing number of applications based on halogen bond (XB), asymmetric catalysis purely based on such supramolecular interactions still remains a huge challenge. The first step toward its development is the design of appropriate XB chiral donor molecules with good catalytic properties. In this context, we report the synthesis of a series of iodinated compounds based on the triazole or triazolium ring and possessing the planar chirality of ferrocene. Their XB donor property was attested by X-ray diffraction analysis, showing short I-N and I-F interactions in the triazole-based derivatives and in the tetrafluoroborate salt of a idodotriazolium, respectively. The potential of these compounds to act as XB-based catalysts was demonstrated in the aza-Diels-Alder reaction involving an imine and a diene. Whereas triazole-based derivatives were inactive in this reaction, the triflate salts of iodotriazoliums delivered the expected cycloadduct with high yield.