Disubstituted Ferrocenyl Iodo- and Chalcogenoalkynes as Chiral Halogen and Chalcogen Bond Donors

Asymmetric catalysis based on halogen and chalcogen bonds (XB and ChB) is in its infancy, and the search for new chiral XB and ChB donors represents a crucial step toward its development. In this context, we designed and prepared new motifs containing three key substructures: namely, regions of electron charge density depletion centered on iodine and chalcogen atoms, the ethynyl functionality, and the planar chiral ferrocenyl platform. Nine ferrocenyl iodoalkynes were prepared as pure enantiomers by asymmetric synthesis. The XB donor property of racemic ferrocenyl iodoalkynes was demonstrated in solution in two benchmark reactions: the Ritter reaction and the benzoxazole synthesis from thioamides. In contrast, the ferrocenyl chalcogenoalkynes were far less active in these reactions. The potential of racemic and enantiopure ferrocenyl iodoalkynes as XB donors was also confirmed by X-ray diffraction analysis, showing I center dot center dot center dot C contacts between the electropositive u-hole of the iodine atom and electron-rich it clouds for all crystal structures studied in the solid state.