Anna Wuttig

Electrocatalytic hydrogenation (e -H) provides a sustainable route for converting unsaturated organic substrates under mild conditions using renewable electricity as the driving force. Here, we report an MOF-derived cobalt catalyst for the e -H of acetone and pyridine. A new two-dimensional cobalt metal–organic framework, Co-L0-NS, composed of Co(II) nodes and polyaromatic carboxylate linkers, was synthesized as nanosheets and used as a precursor to generate the active catalyst under cathodic bias. Electrochemical pretreatment induces controlled framework reconstruction to form MD-Cat, a highly dispersed, structurally disordered, Co(OH)2-rich nanocluster material. MD-Cat catalyzes the e -H of acetone to isopropanol with nearly quantitative Faradaic efficiency at optimized potentials and promotes pyridine hydrogenation to piperidine with up to 50% Faradaic efficiency. Comparative studies with electrodeposited cobalt, commercial cobalt nanoparticles, and bulk Co(OH)2 show that the MOF-derived catalyst exhibits superior current densities and product selectivity, which we attribute to its nanoscale morphology and hydroxylated cobalt environment. In situ Co K-edge XAS, XPS, PXRD, ATR-SEIRAS, and STEM analyses indicate that Co remains predominantly in the +2 oxidation state during catalysis while undergoing structural reorganization. Tafel analysis supports a PCET-type mechanism for acetone hydrogenation; while DFT calculations suggest that the Co/Co(OH)2 interface suppresses HER by weakening H* binding while preserving organic-substrate activation. These results highlight MOF-templated electrochemical reconstruction as a promising approach for designing selective e -H catalysts, not only by increasing catalyst accessibility through nanostructuring but also by enabling the formation of unique catalytic motifs that would otherwise be difficult to access using traditional methods.

The reductive activation of C­(sp³)–F bonds enables the derivatization of fluorinated motifs with medicinal value as well as the recycling of fluorochemicals. The electrochemical reductive activation of C­(sp³)–Cl, C­(sp³)–Br, and C­(sp³)–I bonds at Ag electrodes is well-documented and commonly attributed to inner-sphere, surface-mediated pathways. In contrast, experimental support for surface-mediated reductive C­(sp³)–F activation at Ag electrodes remains limited. Here, we report evidence for the adsorption of organic fluorides at polarized Ag electrodes. We compare spectroscopic and voltammetric data of nitrile-tagged benzylic bromide, chloride, and fluoride substrate with their non-halogenated congener. Surface-sensitive and in situ spectroscopic data are consistent with their adsorption on polarized Ag surfaces, including the organic fluoride, prior to Faradaic charge transfer. Voltammetric data demonstrate enhanced reductive activation of organic halides at Ag, including the organic fluoride, compared to glassy carbon. Exposing organic fluoride adsorption at electrified surfaces motivates electrode designs that can exploit surface interactions for the development of electroorganic methods beyond outer-sphere modalities.

Here, we introduce a catalyst design strategy where non-covalent self-assembly enables molecular control over the active site and microenvironment at the same time to drive efficient electrosynthesis in water. Using anthraquinone-catalyzed H₂O₂ electrosynthesis from O₂ under neutral conditions as a model system, we design anthraquinone-functionalized amphiphiles that self-assemble at polarized electrodes in one in situ step via electrostatic and van der Waals interactions. This process pins and concentrates anthraquinone in a hydrophobic microenvironment that increases the basicity of active intermediates, otherwise poorly accessible in the bulk, by 3 pK_a units. The self-assembled catalyst consequently enhances O₂ reduction over the control catalyst that remains in the bulk solution and does not tether to the electrode. As self-assembly is reversible and agnostic to the surface chemistry of the electrode, this strategy can be translated to high-surface-area electrodes, catalyzing O₂ reduction at 924 mol H₂O₂ mol_cat^–1 h^–1 while allowing recovery and reuse of the amphiphile catalyst. Integrating molecular catalysts into amphiphiles that predictively self-assemble at electrodes to program microenvironments around catalytic sites, our study showcases electrode-orthogonal non-covalent self-assembly as a molecularly tunable construct to enhance electrocatalysis.

Fe₄S₄ clusters play essential roles in nature, classically in electron transport but increasingly in newly discovered reactivity or catalysis. These roles have spurred interest in developing synthetic Fe₄S₄ systems and while several molecular and material systems built from Fe₄S₄ clusters have been developed, comparatively few examples of synthetic Fe₄S₄ cluster-based catalysts exist. Herein, we present the use of an Fe₄S₄-based coordination polymer as a catalyst for the direct and selective electroreduction of CO₂ to CO. Computational studies suggest that the reaction proceeds through CO₂ binding to a reduced Fe₄S₄ cluster, followed by a series of protonation, reduction, and H₂O loss steps to yield a CO-bound cluster that can finally exchange with CO₂ to restart the catalytic cycle. CO bound clusters are predicted to be thermodynamically stable, suggesting that carbonyl species might be off-cycle intermediates. Mechanistic CV studies as well as in situ studies by IR spectroscopy provide evidence for carbonyl-ligated clusters, supporting these compounds as unusual examples of small molecule binding to Fe₄S₄ clusters. This work establishes Fe₄S₄ cluster-based coordination polymers as direct electrocatalysts for CO₂ reduction and provides mechanistic insights into how these species mediate catalytic conversions of small molecules.

Halogen atom transfer enables mild and programmable access to carbon-centered radicals from accessible C(sp³) organic halides for synthetic chemistry. Unlocking this fundamental mechanistic step with reusable heterogeneous electrocatalysts requires strategies to identify and molecularly tune interfacial halogen atom transfer at complex electrified interfaces. Here, we reveal that Brønsted acids unlock interfacial halogen-atom transfer of unactivated alkyl bromides at catalytic Ag electrodes near the thermodynamic potential. In the absence of Brønsted acids, electrochemical and in situ spectroscopic data are consistent with the passivation of Ag surfaces by the halogen upon a single turnover, requiring an overpotential of nearly 1.1 V to activate the electrophile that would erode functional-group tolerance. The addition of acids promotes halogen atom transfer by 1.1 V, enabling access to primary carbon-centered radicals under mild conditions. This promotion effect is unique to catalytic Ag electrode surfaces and general across structurally diverse acids, provided that their pK_a falls below a specific threshold. By demonstrating C(sp³)–C(sp³) bond formation, we show that Brønsted acids enable interfacial halogen atom transfer at reusable catalytic electrodes for electroorganic synthesis.

Fe₄S₄ clusters play essential roles in nature, classically in electron transport but increasingly in newly discovered reactivity or catalysis. These roles have spurred interest in developing synthetic Fe4S4 systems and while several molecular and material systems based on Fe₄S₄ clusters have been developed, comparatively few examples of synthetic Fe₄S₄ cluster-based catalysts exist. Herein, we present the use of an Fe₄S₄-based coordination polymer as a catalyst for the direct and selective electroreduction of CO2 to CO. Computational studies suggest that the reaction proceeds through CO2 binding to a reduced Fe4S4 cluster, followed by a series of protonation, reduction, and H2O loss steps to yield a CO-bound cluster that can finally exchange with CO2 to restart the catalytic cycle. CO bound clusters are predicted to be thermodynamically stable, suggesting that carbonyl species might be off-cycle intermediates. Mechanistic CV studies as well as in situ studies by IR spectroscopy provide evidence for carbonyl-ligated clusters, supporting these compounds as unusual examples of small molecule binding to Fe4S4 clusters. This work establishes Fe4S4 cluster-based coordination polymers as direct electrocatalysts for CO2 reduction and provides mechanistic insights into how these clusters mediate catalytic conversions of small molecules.

Halogen atom transfer enables mild and programmable access to carbon-centered radicals from accessible C(sp3) organic halides for synthetic chemistry. Unlocking this fundamental mechanistic step with reusable heterogeneous electrocatalysts requires strategies to identify and molecularly tune interfacial halogen atom transfer at complex electrified interfaces. Here, we reveal that Brønsted acids unlock interfacial halogen-atom transfer of unactivated alkyl bromides at catalytic Ag electrodes near the thermodynamic potential. In the absence of Brønsted acids, electrochemical and in-situ spectroscopic data are consistent with the passivation of Ag surfaces by the halogen upon a single turnover, requiring an overpotential of nearly 1.1 V to activate the electrophile that would erode functional group tolerance. The addition of acids promotes halogen atom transfer by 1.1 V, enabling access to primary carbon-centered radicals under mild conditions. This promotion effect is unique to catalytic Ag electrode surfaces and general across structurally diverse acids, provided that their pKa falls below a specific threshold. By demonstrating C(sp3)‒C(sp3) bond formation, we show that Brønsted acids enable interfacial halogen atom transfer at reusable catalytic electrodes for electroorganic synthesis.

Electrosynthesis of H2O2 from O2 in neutral aqueous media offers direct access to this widely utilized oxidant for point-of-use applications. Yet, active-site non-uniformity of heterogeneous electrocatalysts challenges optimization of reactivity with molecular-level control. Here, we introduce a non-covalent self-tethering molecular catalyst platform to enhance H2O2 electrosynthesis, otherwise sluggish in neutral buffer. We design anthraquinone-functionalized amphiphiles that self-assemble at polarized electrodes in one in-situ step via electrostatic and van der Waals interactions. This process pins and concentrates anthraquinone in a hydrophobic microenvironment that increases the basicity of active intermediates, otherwise poorly accessible in the bulk, by three orders of magnitude. Self-tethering anthraquinone catalyzes O2 reduction at 924 mol H2O2 molcat–1 hr–1, outperforming its non-tethered counterpart, and is recoverable, leaving a neutral H2O2 solution. Integrating uniform molecular catalysts into amphiphiles that predictively self-assemble in tailored microenvironments at electrodes, our studies demonstrate non-covalent self-tethering as a molecularly tunable construct to enhance electrocatalysis.

Electrochemical hydrogenation (e-H) of organic substrates represents a key transformation for advancing industrial electrification and sustainable chemical manufacturing. Here, we represent e-H of acetone and pyridine by cobalt nanoparticles derived from a Co-based MOF. A novel two-dimensional cobalt metal–organic framework, Co-L0-NS, featuring a kgd-type layered topology with Co(II) paddlewheel nodes and polyaromatic linkers, has been synthe-sized and structurally characterized. Electrochemical reduction of Co-L0-NS induces controlled framework recon-struction, producing highly dispersed cobalt nanoparticles that efficiently catalyze the e-H of acetone to isopropanol and show moderate activity toward pyridine reduction to piperidine. In contrast, electrodeposition from aqueous Co²⁺ precursors forms larger, more crystalline metallic Co particles. Spectroscopic and electrochemical analyses, sup-ported by Tafel modeling, indicate a proton-coupled electron-transfer (PCET) mechanism with a rate-determining step exhibiting a Tafel slope of ~150 mV dec⁻¹. These findings highlight how structural features of the parent MOF—open Co sites, two-dimensional connectivity, and redox flexibility—govern nanoparticle formation and catalytic be-havior, providing design principles for MOF-derived cobalt electrocatalysts.