Abstract
This work maps the thermodynamics of electrochemically generated C-nucleophiles for reactive capture of CO2. We identify a linear relationship between the pKa, the reduction potential of a protonated nucleophile (E red ), and the nucleophile's free energy of CO2 binding ( ΔGbindΔGbind<math><mrow><mo>Δ</mo> <msub><mi>G</mi> <mrow><mi>b</mi> <mi>i</mi> <mi>n</mi> <mi>d</mi></mrow> </msub> </mrow> </math> ). Through synergistic experiments and computations, this study establishes a three-parameter correlation described by the equation ΔGbind=−0.78pKa+4.28Ered+20.95ΔGbind=-0.78pKa+4.28Ered+20.95<math><mrow><mo>Δ</mo> <msub><mi>G</mi> <mrow><mi>b</mi> <mi>i</mi> <mi>n</mi> <mi>d</mi></mrow> </msub> <mo>=</mo> <mo>-</mo> <mn>0.78</mn> <mi>p</mi> <msub><mi>K</mi> <mi>a</mi></msub> <mo>+</mo> <mn>4.28</mn> <msub><mi>E</mi> <mrow><mi>r</mi> <mi>e</mi> <mi>d</mi></mrow> </msub> <mo>+</mo> <mn>20.95</mn></mrow> </math> for a series of twelve imidazol(in)ium/N-heterocyclic carbene pairs with an R 2 of 0.92. The correlation allows us to predict the ΔGbindΔGbind<math><mrow><mo>Δ</mo> <msub><mi>G</mi> <mrow><mi>b</mi> <mi>i</mi> <mi>n</mi> <mi>d</mi></mrow> </msub> </mrow> </math> of C-nucleophiles to CO2 using reduction potentials or pKas of imidazol(in)ium cations. The carbenes in this study were found to exhibit a wide range CO2 binding strengths, from strongly CO2 binding to nonspontaneous. This observation suggests that the ΔGbindΔGbind<math><mrow><mo>Δ</mo> <msub><mi>G</mi> <mrow><mi>b</mi> <mi>i</mi> <mi>n</mi> <mi>d</mi></mrow> </msub> </mrow> </math> of imidazol(in)ium-based carbenes is tunable to a desired strength by appropriate structural changes. This work sets the stage for systematic energetic tuning of electrochemically enabled reactive separations.