[OSSO]-Type Chromium(III) Complexes for the Reaction of CO2 with Epoxides

In this work, four new mononuclear Cr(III) complexes (2-5) bearing bis-thioether-diphenolate, [OSSO]-type ligands, were synthesized and characterized. These complexes in combination with bis(triphenylphosphine)iminium chloride (PPNCl) promoted the coupling of CO2 with epoxides. Depending on the type of substrate and the conditions, the reaction results in the selective formation of either polycarbonate or cyclic carbonate. For example, the reactions in the presence of complex 2 led to the exclusive formation of poly(cyclohexene carbonate, PCHC) from cyclohexene oxide (CHO) (TOF up to 39 h(-1), at T=45-100 degrees C, time=24 h, pCO(2)=20 bar, epoxide/2 (mol/mol)=1000, and PPNCl/2=0.5-2.0 mol %). Under the same conditions and PPNCl/2=0.5-5.0 mol %, the reactions of CO2 with styrene oxide (SO), epichlorohydrin (ECH), 1,2 epoxydodecane (EDD), and allyl glycidyl ether (AGE) have shown selective conversion to the corresponding cyclic carbonates (TOF up to 41 h(-1)).

Automated summary

In this study, four new mononuclear Cr(III) complexes bearing [OSSO]-type bis-thioether-diphenolate ligands were synthesized and characterized. These complexes, in combination with PPNCl, were found to promote the coupling of CO2 with epoxides, leading to the selective formation of either polycarbonate or cyclic carbonate depending on the substrate and reaction conditions.