Efficient and Reusable Iron Catalyst to Convert CO2 into Valuable Cyclic Carbonates.

Ana P C Ribeiro,Peter Goodrich,Luísa M D R S Martins

doi:10.3390/molecules26041089

Abstract

The production of cyclic carbonates from CO2 cycloaddition to epoxides, using the C-scorpionate iron(II) complex [FeCl2{κ3-HC(pz)3}] (pz = 1H-pyrazol-1-yl) as a catalyst, is achieved in excellent yields (up to 98%) in a tailor-made ionic liquid (IL) medium under mild conditions (80 °C; 1–8 bar). A favorable synergistic catalytic effect was found in the [FeCl2{κ3-HC(pz)3}]/IL system. Notably, in addition to exhibiting remarkable activity, the catalyst is stable during ten consecutive cycles, the first decrease (11%) on the cyclic carbonate yield being observed during the 11th cycle. The use of C-scorpionate complexes in ionic liquids to afford cyclic carbonates is presented herein for the first time.

Highlights

Molecules 2021, 26, 1089. https://Over the last few decades, it has become clear that sharply increasing anthropogenicCO2 emissions is affecting the climate stability of the biosphere [1]
The knowledge [9,14,15,16,17] that some types of ionic liquids are able to catalyze the cycloaddition of CO2 to epoxides prompted us to perform a series of experiments with the green, commercially available and affordable ionic liquids (IL) depicted in Figure 2 and selected model epoxides (Scheme 1)
(0.3%mol vs. epoxide), IL (8.3–18.8 mol), CO2 (8 bar), 24 h, 80 ◦ C) were very low (up to 5%, for [bmim][N(CN)2 ]), even in the presence of promoting [Bu4 N]Br [36,37]

Summary

Introduction

Molecules 2021, 26, 1089. https://Over the last few decades, it has become clear that sharply increasing anthropogenicCO2 emissions is affecting the climate stability of the biosphere [1]. Among the possible strategies to use captured CO2 , its catalytic reaction with epoxides to produce cyclic carbonates is one of the most promising applications as a renewable carbon source. Further improvements are needed, in particular, in (i) controlling the selectivity (to impair polycarbonates formation); (ii) achieving suitable catalytic activities for less reactive substrates (e.g., sterically hindered and internal epoxides); (iii) searching for milder efficient reaction conditions (high temperatures and pressures are associated with additional, indirect CO2 emissions, limiting their value from a technological standpoint); and (iv) finding active and selective catalysts able to be recycled and reused in consecutive cycles

Methods

Results

Conclusion