Probing new DABCO-F based ionic liquids as catalyst in organic synthesis

Abstract

The use of ionic liquids as an alternative to the traditional organic solvents offers many advantages, such as their (relatively) low cost of production, ease of handling and storage, high thermal stability, non-volatility, and ability to dissolve different organic and inorganic compounds. The use of ionic liquids for organic syntheses is also sustainable and environmentally friendly as they can be easily recovered and recycled after use. Herein we have synthesized 1,4-diazabicyclo[2.2.2]octane (DABCO)-based ionic liquids with fluoride anion, hence DABCO-C5-F and DABCO-C7-F, containing C5 and C7 alkyl chains respectively, were synthesized and characterized. Thermal studies (TGA/DSC) were also carried out to find out the decomposition temperature (and hence the working temperature range) of the ionic liquids. Moreover, quantum mechanical calculations were performed to obtain the optimized geometry configuration of ionic liquids and their stability was evaluated via binding energy calculation obtained from the MP2 method on the optimized structures. Finally, the DABCO ionic liquids were investigated for their efficiency for the synthesis of different organic compounds (indoles and 1,4-dihydropyridines), which were prepared in good to excellent yields indicating that these DABCO-F can be successfully utilized in organic syntheses by their dual role as ionic liquid and as a catalyst.