Re-cycling carbon dioxide with iron". The synthesis of cyclic organic carbonates in high yield, stereo- and chemo-selectivity was accomplished through the coupling of carbon dioxide and epoxides, catalysed by a novel air-stable and easy-to-handle thioether-triphenolate iron(iii) complex

The selective conversion of variously substituted epoxides into the corresponding cyclic carbonates under mild reaction conditions was achieved with mononuclear Fe(III) complexes bearing bis-thioether-diphenolate [OSSO]type ligands, in combination with tetrabutylammonium bromide (TBAB). For example, propylene carbonate was obtained in 1 h at 35 °C (turnover frequency, TOF = 290 h −1 ), from propylene oxide and 1 bar of CO 2 pressure, using 0.1 mol % of the Fe(III) complex and 0.5 mol % of TBAB. Product divergence is observed only for cyclohexene oxide toward the exclusive formation of the aliphatic polycarbonate (TOF = 165 h −1 at 80 °C and 1 bar of CO 2 pressure, using 0.1 mol % of the Fe(III) complex and 0.1 mol % of tetrabutylammonium chloride). Kinetic investigations indicated reaction orders of two and one, with respect to the Fe(III) complex, for the production of propylene carbonate and the poly(cyclohexene carbonate), respectively. The enthalpy and entropy of activation were determined using the Eyring equation [for propylene carbonate: ΔH ‡ = 8.4 ± 0.7 kcal/mol and ΔS ‡ = −33 ± 3 cal/(mol• K); for poly(cyclohexene carbonate): ΔH ‡ = 11.9 ± 0.3 kal/mol and ΔS ‡ = −36 ± 2.2 cal/(mol•K)]. Supported by density functional theory based investigations, we propose a mechanistic scenario in which the rate-limiting step is the bimetallic ring opening of the epoxide, in the case of propylene carbonate, and the monometallic insertion of the epoxide in the growing polymer chain, in the case of poly(cyclohexene carbonate).

A visible‐light driven Suzuki cross‐coupling reaction was performed with colored and bench‐stable arylazosulfones in the presence of Ph3PAuCl (5 mol %) as the catalyst. The absence of a photocatalyst, along with the use of commercially available and easy‐to‐handle arylboronic acids underline the novelty and synthetic usefulness of the protocol. A reaction mechanism involving the generation of an aryl radical as the key intermediate has been proposed on the basis of experimental investigations.

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.