Efficient Synthesis of Alkane-Bridged N,N’-Diaryl Bisimidazolium Chlorides under Solvent-Free Conditions

Effect of methyl-ene versus ethyl-ene linkers on structural properties of tert-butyl and mesityl bis-(imidazolium) bromide salts

The crystal structures of ligand precursor bis-(imidazolium) salts 1,1'-methyl-enebis(3-tert-butyl-imidazolium) dibromide monohydrate, C15H26N4 +·2Br-·H2O or [ tBuNHC2Me][Br]2·H2O, 1,1'-(ethane-1,2-di-yl)bis-(3-tert-butyl-imidazolium) dibromide dihydrate, C16H28N4 +·2Br-·2H2O or [ tBuNHC2Et][Br]2·2H2O, 1,1'-methyl-enebis[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide dihydrate, C25H30N4 2+·2Br-·2H2O or [MesNHC2Me][Br]2·2H2O, and 1,1'-(ethane-1,2-di-yl)bis-[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide tetra-hydrate, C26H32N4 2+·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 ortho-rhom-bic 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 mol-ecules of water.

Synthesis of a Series of Pyridine-Functionalised Benzoimidazole-Based N-Heterocyclic Carbene Ligands

A series of pyridine-functionalised bis(benzoimidazolium) dichlorides, dibromides and dihexafluorophosphate with different alkyl bridged length ( n = 2–4) were synthesised in high yield. All the compounds are new and fully characterised by 1H and 13C NMR, IR and elemental analyses.

Solvent–Free Synthesis of Some Triazole-Based Bis(N-Heterocyclic Carbene) Ligands

Two series of bistriazolium dibromides with different alkyl bridged length (n = 2–4) were synthesised through a simple solvent-free method. Six of these compounds were prepared from the reaction of 1-R-1H-1,2,4-triazole with dibromoalkane in moderate to excellent yield (45–98%). However, the other six compounds were prepared from the reaction of alkyl bridged bistriazole with bromoalkane in 55–99% yield. All compounds are new and were fully characterised by IR, NMR and elemental analyses.