Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications

Chemical Reviews · 2021 · 435 citations

• Chemistry
• Computational chemistry
• Thermodynamics

) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.

Base-Directed Photoredox Activation of C–H Bonds by PCET

The Journal of Organic Chemistry · 2020 · 17 citations

• Chemistry
• Photochemistry
• Stereochemistry

driving force trend determined for thermal MS-CPET. Analogous photoredox catalysis enables C-H activation and H/D exchange in a number of additional substrates with favorably positioned bases. Mechanistic studies support our hypothesis that MS-CPET is a viable pathway for bond activation for substrates in which the C-H bond is weak, while stepwise carboxylate oxidation and hydrogen atom transfer likely predominate for stronger C-H bonds.

Potential Economic Feasibility of Direct Electrochemical Nitrogen Reduction as a Route to Ammonia

ACS Sustainable Chemistry & Engineering · 2020 · 123 citations

• Environmental science
• Process engineering
• Chemistry

The Haber–Bosch process produces ammonia from hydrogen and nitrogen gases in a globally important energy-intensive process that uses coal or natural gas as a fuel and hydrogen source. Direct electrochemical ammonia synthesis from nitrogen and water using renewable energy sources presents an alternative to the Haber–Bosch process that would be more sustainable. Additionally, the different production structure of direct electrochemical nitrogen reduction technology suggests a supply chain alternative to the ammonia industry and a method for load leveling of the electrical grid. This alternative route to ammonia from dinitrogen would require smaller capital investments than the Haber–Bosch process and would not require a fossil fuel supply. The impact of dynamic electrical power pricing is analyzed for a system that could take advantage of pricing volatility. We show that, under certain scenarios, at achievable levels of energy efficiency with a future electrocatalyst, direct nitrogen reduction would be economically competitive or advantageous compared with Haber–Bosch-based ammonia production.

Highly Diastereoselective Functionalization of Piperidines by Photoredox-Catalyzed α-Amino C–H Arylation and Epimerization

Journal of the American Chemical Society · 2020 · 82 citations

• Chemistry
• Photochemistry
• Stereochemistry

oxidation. Following the rapid and unselective C-H arylation reaction, a slower epimerization occurs to provide the high diastereomer ratio observed for a majority of the products. Several stereoisomerically pure products were resubjected to the reaction conditions, each of which converged to the experimentally observed diastereomer ratios. The observed distribution of diastereomers corresponds to a thermodynamic ratio of isomers based upon their calculated relative energies using density functional theory (DFT).

Determining Proton-Coupled Standard Potentials and X–H Bond Dissociation Free Energies in Nonaqueous Solvents Using Open-Circuit Potential Measurements

Journal of the American Chemical Society · 2020 · 150 citations

• Chemistry
• Physical chemistry
• Inorganic chemistry

scale in the solvent of interest. Consequently, the OCP approach yields more accurate thermochemical values and should be general to any solvent mixture compatible with electrochemical measurements. The longer time scale of OCP measurements enables accurate thermochemical measurements for redox couples with irreversible or distorted electrochemical responses by cyclic voltammetry, provided the PCET reaction is chemically reversible. Recommendations for successful OCP measurements and limitations of the approach are discussed, including the current inability to measure processes involving C-H bonds. As a straightforward and robust technique to determine nonaqueous PCET thermochemistry, these OCP measurements will be broadly valuable, with applications ranging from fundamental reactivity studies to device development.