Dihydroxybenzene-derived ILs as Halide-Free, Single-component Organocatalysts for CO2 Insertion Reactions

A series of dihydroxybenzene-derived ILs was synthesised via a halide-free, eco-friendly methodology and fully characterized. Their activity as single component catalyst towards synthesis of cyclic organic carbonates (COCs) via CO2 insertion into terminal epoxides was evaluated, observing that methyltrioctylammonium hydroquinolate, [N1888][HYD], was the most active catalyst in the proposed optimized conditions ([N1888][HYD] 10 % mol, T=120 °C, t=6 h, p0(CO2)=2.0 MPa, 12 examples, conversion >99 %, yield up to 98 %). Interestingly, [N1888][HYD] was also an active catalyst for CO2 insertion reactions with cyclohexene oxide (CHO), observing formation of both the COC and polycarbonate product. It is proposed that for p0(CO2)≥1.0 MPa, the catalytically active species is the hemicarbonate derivative of the hydroquinolate anion, active towards epoxide ring opening via an unusual hemicarbonate-alkoxide pathway.