Homogeneous Iron Catalysts in the Reaction of Epoxides with Carbon Dioxide

Abstract

Among the attempts to consolidate the so‐called circular economy, the conversion of carbon dioxide (CO2) into added‐value products has gained more and more attention during the last three decades. One of the feasible applications of CO2 as a C1 building block is its incorporation into cyclic organic carbonates (COCs) and aliphatic polycarbonates (APCs) by reaction with epoxides. A plethora of homogeneous catalytic systems has been reported to promote this reaction, based mainly on magnesium, aluminium, cobalt, chromium and zinc complexes. Despite the abundance and low toxicity of iron, only few examples of catalysts based on this metal had been reported until fifteen years ago, and relevant advances were made only during the last decade. This review seeks to cover this progress and to give a renewed impulse for further research into iron utilisation in this kind of catalysis.

Efficient Aluminum Catalysts for the Chemical Conversion of CO2 into Cyclic Carbonates at Room Temperature and Atmospheric CO2 Pressure

“…Several catalyst systems, including metal-based catalystsa nd organocatalysts, have been reportedf or converting CO 2 into cyclic carbonates at room temperature and 1bar CO 2 . [3,5] Aluminum, the most abundant metal in the earth'sc rust (the metals are in the order Al, Fe, Ca, Na, K, Mg, and Ti), is ap articularly attractive metal fort his study,o wing to itsl ow cost, low toxicity, and high Lewis acidity.H owever, only af ew examples of efficient nontoxic catalysts with aluminum metal centers capable of operating at ambient temperaturea nd 1bar CO 2 are known ( Figure 1). [6] Styrene oxide is usually used as the model substrate for coupling reactions with CO 2 because it has moderate reactivity relative to other epoxides, along with lower toxicitya nd ah igherb oiling point.…”

“…ties are defined by turnovern umbers (TONs) of 8.4-39.2 and turnoverf requencies (TOFs) of 0.63-3.73h À1 , [6] which are slightly higher than organocatalysts, but organocatalysts are among the least active catalysts for the synthesis of cyclic carbonates under ambient conditions. [5] Thus, the development of new, more active Al-basedc atalysts ystemst hat allow lower catalyst loadings( < 1.0 mol %) and afford high TONs (> 100)u nder ambient conditions is needed.…”

Cyclic Polyester Formation with an [OSSO]‐Type Iron(III) Catalyst

“…[5] Amongo thers, polymers with ac yclic topologya re an intriguing synthetic target because the lack of chain-ends and the high conformational constraintl ead to materialp roperties that are different from their linear analogues. [28] In recent years,wehave developed anumber of Fe catalystsf or the activation of CO 2 and oxiranes for the production of carbonates [29][30][31] anda chieved the production of aliphatic polycarbonates (APCs) by using an [OSSO]-typel igand system. [8] However,t he formation of cyclic polyesters remains a challenge.…”

“…[9] Such materials are highly attractive foru se in spe-cialized fields such as biomedicine. [28] In recent years,wehave developed anumber of Fe catalystsf or the activation of CO 2 and oxiranes for the production of carbonates [29][30][31] anda chieved the production of aliphatic polycarbonates (APCs) by using an [OSSO]-typel igand system. In this regard, the use of ac atalytic system based on ab iocompatiblem etal such as Fe would be of great interest because it would reduce hazards derived from metal residues in the final product.…”

“…In this regard, the use of ac atalytic system based on ab iocompatiblem etal such as Fe would be of great interest because it would reduce hazards derived from metal residues in the final product. [28] In recent years,wehave developed anumber of Fe catalystsf or the activation of CO 2 and oxiranes for the production of carbonates [29][30][31] anda chieved the production of aliphatic polycarbonates (APCs) by using an [OSSO]-typel igand system. Actually, the number of reports in which the production of cAPEs by means of aw ell-defined metal complex is described is limited, [24] and mosti nvolve the use of Al- [25][26][27] and Zn-based catalysts.…”