Activation of β-diketones for CO2 capture and utilization

Herein, we explore the use of β-diketones for CO2 fixation and utilization based on their dual Brønsted acid/Lewis base character upon activation by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and zinc bromide (ZnBr2), respectively. The effect of tautomerization on the chemical fixation of CO2 was investigated using different β-diketone compounds, namely, acetylacetone (ACAC), dibenzoylmethane (DBM) and dimedone (DMD) dissolved in dimethyl sulfoxide and activated by DBU. Spectroscopic data demonstrated that the activated ACAC can capture atmospheric CO2 through the formation of both keto- and enol-carboxylated adducts, with the ability to evolve the enol form of the ionic organic carbonate adduct upon direct exposure to CO2. Meanwhile activated DBM and DMD showed the exclusive formation of the enol-organic carbonate adducts once bubbled with CO2. Volumetric uptake measurements indicated that the chemisorption capacities of ACAC and DBM (2.38 mmol CO2 per g sorbent) were higher than DMD (1.59 mmol CO2 per g sorbent). Additionally, the chemical fixation of CO2 into cyclic carbonates (CCs) was achieved by in situ complexation of the investigated β-diketones with a zinc ion. The catalytic systems were able to catalyze the transformation of several terminal oxiranes into the corresponding CCs under atmospheric CO2 pressure with excellent conversions. Interestingly, the catalytic system showed the ability to convert the naturally occurring pinene oxide into dimeric pinene carbonate.