The Chloroazaphosphatrane Motif for Halogen Bonding in Solution

Chloroazaphosphatranes, the corresponding halogenophosphonium cations of the Verkade superbases, were evaluated as a new motif for halogen bonding (XB). Their modulable synthesis allowed for synthetizing chloroazaphosphatranes with various substituents on the nitrogen atoms. The binding constants determined from NMR titration experiments for Cl-, Br-, I-, AcO-, and CN- anions are comparable to those obtained with conventional iodine-based monodentate XB receptors. Remarkably, the protonated azaphosphatrane counterparts display no affinity for anions under the same conditions. The strength of the XB interaction is, to some extent, related to the basicity of the corresponding Verkade superbase. The halogen bonding abilities of this new class of halogen donor motif were also revealed by the Delta delta(P-31) NMR shift observed in CD2Cl2 solution in the presence of triethylphosphine oxide (TEPO). Thus, chloroazaphosphatranes constitute a new class of halogen bond donors, expanding the repertory of XB motifs mainly based on C-Ar-I bonds.

Automated summary

Chloroazaphosphatranes have been identified as a new class of halogen bond donors with modulable synthesis, showing comparable binding abilities to conventional iodine-based monodentate XB receptors and a relationship with the basicity of Verkade superbases. The strength of the XB interaction was revealed by the Delta delta(P-31) NMR shift observed in CD2Cl2 solution in the presence of triethylphosphine oxide (TEPO), expanding the repertory of XB motifs based on C-Ar-I bonds.