[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 °C, time=24 h, pCO2=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). Four novel [OSSO]‐based‐Cr(III) complexes (2‐5) were synthesized and characterized. Their catalytic activity was investigated in CO2/epoxide coupling reaction in the presence of PPNCl as co‐catalyst. Among the reported complexes, catalyst 2 showed the best catalytic activity in the exclusive formation of polycarbonates (PPC, PCHC, PVCH, and PHC) with a selectivity of 83 % and more in all cases.