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, [N-1888][HYD], was the most active catalyst in the proposed optimized conditions ([N-1888][HYD] 10 % mol, T=120 degrees C, t=6 h, p(0)(CO2)=2.0 MPa, 12 examples, conversion >99 %, yield up to 98 %). Interestingly, [N-1888][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 p(0)(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.

Automated summary

A series of dihydroxybenzene-derived ILs were synthesized in a halide-free, eco-friendly manner and fully characterized. The most active catalyst for CO2 insertion into terminal epoxides to synthesize cyclic organic carbonates (COCs) was found to be methyltrioctylammonium hydroquinolate, [N-1888][HYD], under the proposed optimized conditions ([N-1888][HYD] 10% mol, T=120 degrees C, t=6 h, p(0)(CO2)=2.0 MPa, 12 examples, conversion >99%, yield up to 98%). Interestingly, [N-1888][HYD] also showed activity as a catalyst for CO2 insertion reactions with cyclohexene oxide (CHO), resulting in the formation of both COC and polycarbonate products. It is suggested that the catalytically active species for p(0)(CO2)>= 1.0 MPa is the hemicarbonate derivative of the hydroquinolate anion, which acts through an unusual hemicarbonate-alkoxide pathway for epoxide ring opening.