Synthesis of 2,2'-biimidazolium-based ionic liquids: use as a new reaction medium and ligand for palladium-catalyzed suzuki cross-coupling reactions.
Neat reactions of 2,2'-biimidazole with an excess of alkyl or polyfluoroalkyl iodides at 140 degrees C, followed by anion exchange with LiN(SO(2)CF(3))(2) or KPF(6), gave the diquaternary salts 3a-k in >80% yields. However, by controlling the reaction stoichiometry, 2,2'-biimidazole can also be monoquaternized with the same electrophiles at 100 degrees C under similar conditions. Subsequent metathesis reactions with LiN(SO(2)CF(3))(2) or KPF(6) resulted in the ionic liquids 4a-m in high yields. Thermal properties were determined with a differential scanning calorimeter (DSC) and a thermogravimetric analyzer (TGA). Most of the monoquaternary salts are room-temperature ionic liquids. 1,3,1'-Tributyl-2,2'-biimidazolium hexafluorophosphate was demonstrated to be an excellent solvent and ligand for palladium-catalyzed Suzuki cross-coupling reactions. The catalytic ionic liquid system may be recycled at least 14 times without a significant decrease in catalytic performance.
Xiao
Ji-Chang
JC
Department of Chemistry, University of Idaho, Moscow, ID 83844-2343, USA.
Shreeve
Jean'ne M
JM