More Like this

1. Towards Immobilized Proton-Coupled Electron Transfer Agents for Electrochemical Carbon Capture from Air and Seawater

   https://doi.org/10.1149/1945-7111/ad4a0f  

   Ali, Fawaz; Bilger, David; Patamia, Evan_D; Andrew, Trisha_L; Kwabi, David_G (May 2024, Journal of The Electrochemical Society)

   Electrochemical CO₂separation has drawn attention as a promising strategy for using renewable energy to mitigate climate change. Redox-active compounds that undergo proton-coupled electron transfer (PCET) are an impetus for pH-swing-driven CO₂capture at low energetic costs. However, multiple barriers hinder this technology from maturing, including sensitivity to oxygen and the slow kinetics of CO₂capture. Here, we use vapor phase chemistry to construct a textile electrode comprising an immobilized PCET agent, poly(1-aminoanthraquinone) (PAAQ), and incorporate it into redox flow cells. This design contrasts with others that use dissolved PCET agents by confining proton-storage to the surface of an electrode kept separate from an aqueous, CO₂-capturing phase. This system facilitates carbon capture from gaseous sources (a 1% CO₂feed and air), as well as seawater, with the latter at an energetic cost of 202 kJ/mol_CO2, and we find that quinone moieties embedded within the electrode are more stable to oxygen than dissolved counterparts. Simulations using a 1D reaction-transport model show that moderate energetic costs should be possible for air capture of CO₂with higher loadings of polymer-bound PCET moieties. The remarkable stability of this system sets the stage for producing textile-based electrodes that facilitate pH-swing-driven carbon capture in practical situations. 

   more » « less
2. Coordination-Induced Bond Weakening and Electrocatalytic Proton-Coupled Electron Transfer of a Ruthenium Verdazyl Complex

   https://doi.org/10.1021/acs.inorgchem.3c02775  

   Galvin, Conor M.; Marron, Daniel P.; Dressel, Julia M.; Waymouth, Robert M. (January 2024, Inorganic Chemistry)

   Coordination of the leucoverdazyl ligand 2,4-diisopropyl-6-(pyridin-2-yl)-1,4-dihydro-1,2,4,5-tetrazin-3(2H)-one VdH to Ru significantly weakens the ligand’s N-H bond. Electrochemical measurements show that the metalated leucoverdazyl Ru(VdH)(acetylacetonate)2 RuVdH has a lower pKa (-5 units), BDFE (-7 kcal/mol), and hydricity (-22 kcal/mol) than the free ligand. DFT calculations suggest that the increased acidity is in part attributable to the stabilization of the conjugate base Vd-. When free, Vd- distorts to avoid an 8πe- antiaromatic state, but it remains planar when bound to Ru. Proton-coupled electron transfer (PCET) behavior is observed for both the free and metalated leucoverdazyls. PCET equilibrium between Vd radical and TEMPOH affords a VdH BDFE that is in good agreement with that obtained from electrochemical methods. RuVd exhibits electrocatalytic PCET donor behavior. Under acidic conditions, it reduces the persistent trityl radical ·CAr3 (Ar = p-tert-butylphenyl) to the corresponding triarylmethane HCAr3 via net 1e-/1H+ transfer from RuVdH. 

   more » « less
3. Synthesis of [Os(bpy) ₂ (py)(OH ₂ )](PF ₆ ) _x substituted pyridine complexes; characterization of a singly bridged H ₃ O ₂ ⁻ ligand

   https://doi.org/10.1039/D5DT00419E  

   Sun, Jiangtian; Sun, Jingwen; Jolly, Brandon J; Riu, Martin-Louis Y; Kerr, Tyler A; Lai, Yi-An; Pung, Michael J; Liu, Chong; Nava, Matthew (March 2025, Dalton Transactions)

   In situelectrochemical analysis enables access to metal aquo PCET model complexes which are synthetically elaborated and speciation was determined. 

   more » « less
4. Evaluating Diazene to N ₂ Interconversion at Iron‐Sulfur Complexes

   https://doi.org/10.1002/chem.202304072  

   Hooper, Reagan_X; Wertz, Ashlee_E; Shafaat, Hannah_S; Holland, Patrick_L (March 2024, Chemistry – A European Journal)

   Abstract Biological N₂reduction occurs at sulfur‐rich multiiron sites, and an interesting potential pathway is concerted double reduction/ protonation of bridging N₂through PCET. Here, we test the feasibility of using synthetic sulfur‐supported diiron complexes to mimic this pathway. Oxidative proton transfer from μ‐η¹ : η¹‐diazene (HN=NH) is the microscopic reverse of the proposed N₂fixation pathway, revealing the energetics of the process. Previously, Sellmann assigned the purple metastable product from two‐electron oxidation of [{Fe²⁺(PPr₃)L¹}₂(μ‐η¹ : η¹‐N₂H₂)] (L¹=tetradentate SSSS ligand) at −78 °C as [{Fe²⁺(PPr₃)L¹}₂(μ‐η¹ : η¹‐N₂)]²⁺, which would come from double PCET from diazene to sulfur atoms of the supporting ligands. Using resonance Raman, Mössbauer, NMR, and EPR spectroscopies in conjunction with DFT calculations, we show that the product is not an N₂complex. Instead, the data are most consistent with the spectroscopically observed species being the mononuclear iron(III) diazene complex [{Fe(PPr₃)L¹}(η²‐N₂H₂)]⁺. Calculations indicate that the proposed double PCET has a barrier that is too high for proton transfer at the reaction temperature. Also, PCET from the bridging diazene is highly exergonic as a result of the high Fe^3+/2+redox potential, indicating that the reverse N₂protonation would be too endergonic to proceed. This system establishes the “ground rules” for designing reversible N₂/N₂H₂interconversion through PCET, such as tuning the redox potentials of the metal sites. 

   more » « less
5. Coordination-induced bond weakening and small molecule activation by low-valent titanium complexes

   https://doi.org/10.1039/D3DT03454B  

   Oloyede, Ugochinyere N; Flowers, Robert A (February 2024, Dalton Transactions)

   The coordination of small molecules to low valent titanium complexes provides a powerful platform for the transformation of challenging substrates either through PCET reactions or bond-weakening induced by π-back donation of electrons from Ti. 

   more » « less