The use of carbon dioxide (CO2) as a C1 building block is an attractive process as it is abundant, non-toxic, non-flammable, and cheap. However, the activation of CO2 is energy intensive, due to the oxidation state of carbon. Metal containing ionic liquids (ILs) have recently shown good prospect as catalysts for the formation of cyclic carbonates through the fixation of CO2 in epoxides. In addition to their catalytic properties, metal containing ILs show interesting properties, like response to an external magnetic field. This can be used for new possible applications for magnetic and electrochromic switching. Herein, we describe the synthesis, characterization and catalytic applications of a well-defined imidazolium based iron-containing IL [BMIm][Fe(NO)2Cl2]. Such a characterization enabled us to establish the actual structure of the iron-based containing IL, which was found to be an active catalyst for the cycloaddition of CO2 to epoxides, giving high conversions for various substrates under near ambient conditions. The complex works as a bifunctional catalyst without any additive or co-catalyst, in which the metal center plays a role as Lewis acid and the chloride anion, as part of the [BMIm][Cl] moiety, acts as nucleophile. The reaction mechanism and the nature of the different species involved in the catalytic cycle were investigated by experimental studies. Such experiments demonstrated that the imidazolium moiety is involved in the catalytic process, whereas the reaction proceeds with retention of configuration through a nucleophilic attack to the Cβ of the epoxide. In addition, kinetic studies showed that the process followed first-order kinetics regarding epoxide concentration and revealed the presence of a fast pre-equilibrium in which the iron-containing ionic liquid [BMIm][Fe(NO)2Cl2] (non-reactive state) dissociates at high temperature and generates the true-catalytically active species, [BMIm][Cl] + [Fe(NO)2Cl]. On the basis of these experiments, a catalytic cycle was proposed.

Fe-based magnetic ionic liquids: Synthesis, characterization, and application for carbon dioxide fixation

256th National Meeting (2018)

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