Coupling of Carbon Dioxide with Epoxides Efficiently Catalyzed by Thioether‐Triphenolate Bimetallic Iron(III) Complexes: Catalyst Structure–Reactivity Relationship and Mechanistic DFT Study

Abstract

As erieso fd inuclear iron(III) I complexes supported by thioether-triphenolate ligands have been preparedt oa ttain highly Lewis acidic catalysts. In combination with tetrabutylammonium bromide (TBAB) they are highly active catalysts in the synthesis of cyclic organic carbonates through the coupling of carbon dioxide to epoxides with the highest initial turnoverf requencies reported to date for the conversion of propylene oxide to propylene carbonate for iron-based catalysts (5200h À1 ;1 20 8 8C, 2MPa, 1h). In particular, these complexes are shown to be highly selective catalysts for the coupling of carbon dioxidet oi nternalo xiranes affording the corre-sponding cyclic carbonates in good yield and with retentiono ft he initial stereochemical configuration. A density functional theory (DFT)i nvestigation provides ar ational for the relative high activity found for these Fe(III) complexes,s howing the fundamental role of the hemilabile sulfur atom in the ligand skeleton to promote reactivity.N otably,i ns pite of the dinuclear nature of the catalyst precursor only one metal center is involved in the catalytic cycle. Scheme 1. Synthesis of the proligands L1-L6 and the corresponding iron(III) complexes 1--6.

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

“…[29] HR-MALDI Fourier-transform ion cyclotron resonance MS (HR-MALDI FT-ICR MS) measurements of polymers were performed by using aB ruker Solaris XR instrument. To luene (99.5 %; Sigma-Aldrich) and THF (99 %; Sigma-Aldrich) were used as received or heated to reflux for 48 ho ver sodium or sodium ketyls and distilled before use for moisture-and oxygen-sensitive reactions.…”

“…[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.…”

Effect of an Al(III) Complex on the Regio- and Stereoisomeric Formation of Bicyclic Organic Carbonates

“…[37][38][39] The area of cyclic carbonate synthesis has witnessed a spectacular growth over the last decade 2,3,30-32 with a primary focus on the development of improved and more sustainable catalysts for the [3+2] cycloaddition of epoxides and CO2. [40][41][42][43] The (dia)stereoselective formation of more complex cyclic organic carbonates, 25,44,45 however, remains underdeveloped. It is generally assumed that the formation of a cyclic carbonate from epoxides and CO2 follows a typical threestep sequence involving epoxide ring opening induced by the (binary) catalyst, subsequent activation of the CO2 molecule by the intermediate alkoxide and termination through cyclization releasing the desired product.…”