Effect of methylene versus ethylene linkers on structural properties of tert-butyl and mesityl bis(imidazolium) bromide salts

Abstract

The crystal structures of ligand precursor bis(imidazolium) salts 1,1′-methylenebis(3-tert-butylimidazolium) dibromide monohydrate, C15H26N4+·2Br−·H2O or [tBuNHC2Me][Br]2·H2O, 1,1′-(ethane-1,2-diyl)bis(3-tert-butylimidazolium) dibromide dihydrate, C16H28N4+·2Br−·2H2O or [tBuNHC2Et][Br]2·2H2O, 1,1′-methylenebis[3-(2,4,6-trimethylphenyl)imidazolium] dibromide dihydrate, C25H30N42+·2Br−·2H2O or [MesNHC2Me][Br]2·2H2O, and 1,1′-(ethane-1,2-diyl)bis[3-(2,4,6-trimethylphenyl)imidazolium] dibromide tetrahydrate, C26H32N42+·2Br−·4H2O or [MesNHC2Et][Br]2·4H2O, are reported. At 293 K, [tBuNHC2Me][Br]2·H2O crystallizes in the P21/c space group, while [tBuNHC2Et][Br]2·2H2O crystallizes in the P21/n space group at 100 K. At 112 K, [MesNHC2Me][Br]2·2H2O crystallizes in the orthorhombic space group Pccn while [MesNHC2Et][Br]2·4H2O crystallizes in the P21/c space group at 100 K. Bond distances and angles within the imidazolium rings are generally comparable among the four structures. All four bis(imidazolium) salts co-crystallize with one to four molecules of water.

Keywords

• crystal structure
• bis(imidazolium)
• bidentate nhc
• n-heterocyclic carbene