Synthesis, crystal structure, Hirshfeld surface analysis, DFT calculations and characterization of 1,3-propanediylbis(triphenylphosphonium) monotribromide as brominating agent of double bonds and phenolic rings

This paper presents synthesis and structural characterization of new members of phosphorus-based organic bromides. 1,3-Propanediylbis(triphenylphosphonium) dibromide I and 1,3-propanediylbis(triphenylphosphonium) monotribromide II, as a new brominating agent for double bonds and phenolic rings, were synthesized. ¹H NMR, ¹³C NMR, ³¹P NMR, FT-IR, single crystal X-ray diffraction crystallography, differential scanning calorimetry, thermogravimetric analysis and differential thermal analysis were used to characterize these salts. Thermal and physicochemical stability, simple working up, non-toxicity in comparison to liquid bromine and high yield are some of the advantages of these salts. These salts have good solubility in organic solvents, such as methanol, ethanol, acetone, dichloromethane and THF. Crystallographic data showed that compound I crystallized in the monoclinic crystal system, in P2₁ space group and compound II crystallized in the monoclinic crystal system, in P2₁/c space group and one of the bromide ions was replaced by tribromide ion in II. The crystal packing structures of title compounds were stabilized by various intermolecular interactions, especially of the type C-H∙∙∙π contacts. The molecular Hirshfeld surface analysis and 2D fingerprint analysis revealed that the C∙∙∙H (30.4% for the compound I and 28.3% for compound II) contact, which was related to C-H∙∙∙π interactions, had the major contribution in the crystal architectures. To get more insight about molecular structures of titled compounds, DFT calculations were performed (energy, structural optimization and natural bond orbital analysis). Bromination of double bonds and phenolic rings was carried out to prove the ability of the tribromide salt to bromine such organic substrates.