Renewable Hydride Donors for the Catalytic Reduction of CO₂: A Thermodynamic and Kinetic Study

Abstract

Increasing atmospheric CO 2 concentration and dwindling fossil fuel supply necessitate the search for efficient methods for CO 2 conversion to fuels. Assorted studies have shown pyridine and its derivatives capable of (photo)electrochemically reducing CO 2 to methanol, and some mechanistic interpretations have been proposed. Here, we analyze the thermodynamic and kinetic aspects of the efficacy of pyridines as hydride-donating catalytic reagents that transfer hydrides via their dihydropyridinic form. We investigate both the effects of functionalizing pyridinic derivatives with electrondonating and electron-withdrawing groups on hydride-transfer catalyst strength, assessed via their hydricity (thermodynamic ability) and nucleophilicity (kinetic ability), and catalyst recyclability, assessed via their reduction potential. We find that pyridines substituted with electron-donating groups have stronger hydride-donating ability (having lower hydricity and larger nucleophilicity values), but are less efficiently recycled (having more negative reduction potentials). In contrast, pyridines substituted with electron-withdrawing groups are more efficiently recycled, but are weaker hydride donors. Functional group modification favorably tunes hydride strength or efficiency, but not both. We attribute this problematic coupling between the strength and recyclability of pyridinic hydrides to their aromatic nature and suggest several avenues for overcoming this difficulty.

Predictive energetic tuning of C-Nucleophiles for the electrochemical capture of carbon dioxide

“…pK a values are obtained by creating a linear fit between experimentally determined pK a values and the computed free energy difference – . While it is common to estimate pK a values using an isodesmic approach or use a pre-determined free energy of solvated protons ( Alherz et al., 2018 ; Thapa and Schlegel, 2016 ), we argue that a linear fitting approach avoids any systematic errors in pK a predictions. Figure S3 shows the linear correlation described.…”

“…Because imidazolium cations ImH + are aromatic, the reduction of ImH + to add an electron to the imidazolium π-system results in de-aromatization of the imidazolium ring. Prior studies have shown that aromatic hydrides exhibit a linear correlation between the first reduction potential of the oxidized hydride and the nucleophilicity of the hydride ( Alherz et al., 2018 ; Ilic et al., 2018 ). To verify this correlation for imidazolium salts, we measured E red for a family of imidazolium salts ( Figure S1 and Table S1 ) using normal pulse voltammetry (NPV).…”

Visible-Light Photoinitiation of (Meth)acrylate Polymerization with Autonomous Post-conversion

“…The M06-2X-computed molecular orbitals were viewed using Avogadro. Reductional potential calculations were performed based on the approach developed by Tossell. , Electron densities were computed using atomic polar tensor population analysis. , …”

“…Reductional potential calculations were performed based on the approach developed by Tossell. 56,57 Electron densities were computed using atomic polar tensor population analysis. 58,59 The photophysical properties of λ max , its corresponding molar absorptivity (ε max ), and changes in the electron occupation of active orbitals upon photoexcitation of chromophores were computed using TD-DFT at the M06-2X/6-311++g(d,p)/SMD-acetonitrile level of theory with geometries optimized with DFT at the M06-2X/6-31+g(d,p)/SMD-acetonitrile level of theory.…”

Non-metal photochemical reduction of CO2 to formate with organohydride-recycle strategy

“…Therefore, organomolecules that undergo multi-electron CO2RR are limited. [25][26][27][28][29][30][31][32] Successful examples are reactions using a combination of frustrated Lewis pairs and metalloid hydride species (B-H or Si-H) (Fig. 1C).…”