Thiourea Based Tritopic Halogen Bonding Acceptors

Abstract

Series of thiourea based tritopic receptor molecules were synthesized to be used as building blocks for halogen-bonded assemblies. Here 16 new receptor molecules were synthesized from two different 2,4,6-trialkyl-1,3,5-tris(bromomethyl)benzene starting materials via tris(isothiocyanatomethyl)benzene intermediates. The alkyl substituents in the benzene ring showed to be important for isothiocyanate group formation instead of competing thiocyanate group. The synthesis route allowed us to synthesize the isothiocyanate intermediates and further the receptor molecules without typically used and highly toxic thiophosgene. Synthesized receptor molecules were used to study their halogen bond acceptor properties with diiodotetrafluorobenzene donors by single crystal X-ray diffraction method. We were able to obtain five new crystal structures of halogen bonded complexes, in which all receptors showed two to four accepted C−I···S halogen bonds. The observed halogen bonds were highly directional and showed large variation in C=S···I acceptor angles indicating flexible acceptor properties of sulfur.