Organometallic Electrochemistry: Redox Catalysis Going the Smart Way

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Organometallic Electrochemistry: Redox Catalysis Going the Smart Way

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maintaining the O2 content of our atmosphere. Dioxygen is released in the so-called light-dependent reaction of photosynthesis, when (photo)catalytic H2O cleavage occurs. The primary energy carrier of this reaction is adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). The latter is an equivalent of molecular hydrogen that hydrogenates CO2 during carbon fixation in the Calvin cycle. The (photo)electrocatalytic production of H2 from H2O, and subsequent reverse conversion of H2 into electricity in a fuel cell, and CO2 functionalization into hydrocarbons and/or carbohydrates have thus become prime research targets in electrochemical redox catalysis for scientists and engineers. Another blueprint transformation is given by Nature’s [FeFe] and [NiFe] hydrogenases, which efficiently reduce protons to dihydrogen. In this process, cooperativity between the two metal centers, the secondary sphere ligand functionalities, and the protein matrix enables proton reduction at thermodynamic potentials. Similar mechanisms of cooperativity have been applied for the design of synthetic analogues, resulting in promising electrocatalysts.4 For instance, with [NiFe]-hydrogenases as inspirations, the pendant amine groups of the nickel(II) bis(diphenylphosphine) complex relay protons to the metal center, achieving a catalytic turnover number (TON) of more than 105 s−1 in the hydrogen-evolution reaction.5 Research on these functional models is still thriving and, therefore, is well-documented within this Special Issue. The development of catalysts capable of the selective electrochemical conversion of CO2 to CO is among the major challenges of renewable and sustainable energy research. Again, Nature has mastered this process and points scientists to possible solutions. In an alternative to the Calvin cycle, CO2 fixation under anaerobic conditions predominantly occurs via the so-called Wood−Ljungdahl pathway. The active enzyme is carbon monoxide dehydrogenase (CODH) with a [NiFe4S5] cluster at the active site. It operates by cooperativity between the [NiFe] centers and lysine from the protein backbone to bind and reduce CO2 to CO22−. Upon protonation, CO22− forms CO, with H2O as a side product.6 Immobilization of CODH on the surface of a semiconductor has even demonstrated the potential of this enzyme for photoelectrocatalytic CO2 to CO reduction.7 Unfortunately, owing to its complex structure, highly functional synthetic mimics of the [NiFe4S5] active site have not been reported to date. However, Nature’s underlying concept of driving CO2 reduction through substrate hydrogen bonding facilitated by second-sphere ligand functionalities was successfully implemented, for instance, in nickel-cyclam and iron-porphyrin

odern energy challenges have intensified research efforts to develop electrode materials and metal-based molecular homogeneous and heterogeneous catalysts for fuelforming reactions. Electrocatalyst development has thus become an ever-increasing field of interesting interdisciplinary research, transcending traditional science and engineering borders and attracting chemists, physicists, surface scientists, and materials scientists together with electrical and chemical engineers. Electrocatalysis is expected to play a vital role in finding solutions to the production of reliable, affordable, and environmentally friendly energy, fuels, and chemicalshydrogen, carbon monoxide, methanol, and ammonia, to name a few. This Special Issue, “Organometallic Electrochemistry: Redox Catalysis Going the Smart Way”, takes account of these developments. This issue further demonstrates the global reach of energy research and organometallic chemistry, featuring contributions with authors from 18 countries: Austria, Belgium, Canada, China, France, Germany, India, Ireland, Italy, The Netherlands, Portugal, Russia, Singapore, Spain, Sweden, Switzerland, the U.K., and the U.S. Among other topics, this Special Issue tackles electrochemical carbon dioxide and hydrogen redox chemistry by describing “smart ways” to creatively advance the CO2 thermodynamic problem as well as proton reduction and hydrogen oxidation chemistryall key to the production of sustainable fuels and feedstocks. The inspiring electrochemistry presented here summarizes recent progress, spanning a range of topics from transition-metal catalyst design, testing, and improvement to electrode functionalization and optimization, including mechanistic and theoretical studies. As is often the case, Nature holds the blueprint for success with catalytic transformations of energy-related small molecules, finding precedent in biological processes.1 Scientists and engineers have spent decades studying these systems, trying to unlock their secrets and find ways to mimic them to develop inexpensive, efficient, and environmentally friendly synthetic processes. One of the masterpieces in Nature’s box of tricks, the facile synthesis of ammonia from atmospheric dinitrogen by nitrogenase, for instance, raises particular interest in the field because of the enzyme’s microscopic reverse reaction. Namely, the electrocatalytic oxidation of ammonia for H2 generation is attractive for fuel cell applications.2 In another example, the selective oxidation of methane to methanol finds its biological archetype in methane monooxygenase, and an important technological application of this reaction is the direct methanol fuel cell. The pinnacle of a “perfect” fuel-forming device is likely the combination of enzymes responsible for photosynthesis, which convert light energy, carbon dioxide, and water into chemical energy that ultimatelyin the form of sugarscan be viewed as the “fuel of life” on Earth (ca. 2 × 1011 tons of organic product per year).3 As a bonus, the process’s sole waste product is molecular oxygen, which is indispensable to © 2019 American Chemical Society

Special Issue: Organometallic Electrochemistry: Redox Catalysis Going the Smart Way Published: March 25, 2019 1181

DOI: 10.1021/acs.organomet.9b00111 Organometallics 2019, 38, 1181−1185

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model complexes.8 Because of the tremendous significance to the field, reports on the progress and challenges of electrocatalytic CO2 reduction chemistry are well represented in this Special Issue. Given the high reactivity and toxicity of reducing and oxidizing agents, scaling redox reactions is frequently problematic. Redox reagents for synthesis also often result in significant amounts of waste byproducts, thus requiring expensive separation procedures and proper disposal protocols. These can be bypassed by applying electrochemical redox methods, relying on an electrical power source, appropriate electrode material, and/or a molecular electrocatalyst to achieve the selectively needed to convert a given compound into the desired product. Other advantages of electrochemical synthesis, in comparison with conventional synthetic protocols, are high energy efficiency and tolerance of steric bulk and functional groups.9 Historically, it is interesting to note that one of the first electrocatalytic conversions reportedthe so-called Kolbe reactionwas published as early as 1848. In Kolbe’s electrosynthesis, two carboxylic acids were coupled by decarboxylative dimerization to produce ethane and CO2 (see the cover).10 Nearly 100 years later, this reaction was successfully applied to synthesize important natural products.11 Although the focus of this Special Issue is on small-molecule synthesis and reactivity for energy and fuel applications, an equally vibrant renaissance in electrocatalysis of this type is now taking place in mainstream organic synthesis. For example, recent research has reaffirmed the potential and advantages of organic electrosynthesis for the greener, scalable synthesis of natural products and drugs.12 With all this foundational work to build upon, we can examine the latest work exploring important topics in organometallic electrochemistry. In the field of carbon dioxide reduction catalysis, a significant number of articles are devoted to the archetypal metal tricarbonyl system, namely [M(L)(CO)3(X)], with group 6/7 metal ions (M) and a bidentate chelate ligand (L) that often is a derivative of the well-known bipyridine (bipy) ligand, a newly developed chelate based on an N-heterocyclic carbene (NHC) ligand, or a redox-active entity imparting unique electrochemical properties. Additionally, novel developments of group 8 (iron), 9 (cobalt), and 10 (nickel, palladium) electrocatalysts are featured and the importance of intra- and intermolecular hydrogen-bonding interactions continues to be analyzed. In an effort to contribute to the understanding of electrocatalytic CO2 to CO reduction, researchers led by Andrew Bocarsly (Princeton University) studied the effects of a variety of substituents on bipyridyl ligands of low-valent manganese carbonyl catalysts. Their study reveals that electron-withdrawing substituents on the bipy ligands prevent CO2 reduction, while electron-donating groups support the catalytic ability. Catalyst efficiency improves with increasing steric hindrance of the substituents (DOI: 10.1021/acs. organomet.8b00554). The Italian team around Roberto Gobetto and Carlo Nervi (University of Torino), together with Marc Robert (Université Paris Diderot) and Jan Fiedler (The Czech Academy of Sciences), highlights their joint effort of giving a new spin to electrochemical CO2 reduction and transformation catalysis, also employing [M(bipy)(CO)3X]type complexes. They synthesized and studied novel bipyridine rhenium(I) carbonyl species, sporting additional proton sources bound to the derivatized bipyridine chelators to

investigate performance changes of catalytic CO2 reduction and formate production. In addition, photostimulated conversion of CO2 was studied and a comparison between rhenium and the lighter manganese catalysts is presented (DOI: 10.1021/acs.organomet.8b00588). Aiming for sustainability in a complete device, where CO2 reduction is coupled to water oxidation, the Irish−British team of James Walsh, Charlotte Smith (both Dublin City University), and Alexander Cowan (University of Liverpool) report one of the rare examples of water-soluble electrocatalysts for CO2 to CO reduction. Notably, their manganese polypyridyl complex shows activity over a broad pH range (DOI: 10.1021/acs.organomet.8b00336). František Hartl (University of Reading), together with collaborators in Switzerland and Portugal, investigated organometallic molybdenum carbonyl complexes with differently substituted bipyridine ligands for electrocatalytic CO2 reduction. Their results suggest that the cathodic path of group 6 complexes is closely related to the comprehensively examined diiminesupported group 7 manganese tricarbonyl catalysts (DOI: 10. 1021/acs.organomet.8b00676). Highly interdisciplinary research from the U.S. and Germany, contributed by Mehmed Ertem, David Grills (both Brookhaven National Laboratory), and Biprajit Sarkar (FU Berlin) and headed by Jonathan Rochford (University of Massachusetts, Boston), provides insights into manganese- and rhenium-mediated electrocatalytic CO2 reduction and the operating synergistic metal−ligand redox cooperativity of derivatives of the generally popular manganese and rhenium tricarbonyl complexes, in their case supported by a redoxactive dimethyl oxyquinolate ligand. The one- and twoelectron-reduced species were characterized by a combination of advanced spectroelectrochemical and computational tools, including pulse radiolysis, time-resolved vibrational, and EPR spectroscopy (DOI: 10.1021/acs.organomet.8b00584). In another example, Oana Luca and co-workers (University of Colorado, Boulder), in collaboration with Curtis Moore (UC San Diego’s X-ray crystallography facility), study lowvalent manganese electrocatalysts. In their efforts to develop an improved catalyst for CO2 reduction, they synthesized and investigated novel analogs with an electron-donating, tridentate carbene−pyridine−carbene pincer version of the widely successful NHC ligands. The Luca team has been making a name for itself for the swift determination of the number of electrons exchanged in a given redox event by normal pulse voltammetry (NPV) and diffusion-ordered spectroscopy (DOSY). Employing their specialized analysis to the research reported suggests a one-electron reduction wave for the studied catalyst at the onset of catalytic current increase. This finding is thought provoking, as CO2 reduction by previously studied rhenium and manganese complexes of the [M(bipy)(CO)3X] system, and the corresponding bidentate NHC-pyridine analogues, are considered to occur after a two-electron reduction step of the catalyst (DOI: 10.1021/acs.organomet. 8b00535). In this Special Issue, research from California is focused on the immobilization of homogeneous CO2 reduction catalysts on electrodes. The presented work on a heavier group 7 electrocatalyst, namely an improved, highly potent, and selective rhenium-based CO2 reduction catalyst, is presented by Clifford Kubiak (UC San Diego) and Simon Jones (Jet Propulsion Laboratory). The groups report successful attachment of the studied molecular rhenium catalyst to a carbon 1182

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electrode surface by electropolymerization and, in a first-timeever successful effort, they achieved attachment of a CO2 reduction catalyst by “click” chemistry (DOI: 10.1021/acs. organomet.8b00547). In a similarly exciting and topical study, Louise Berben and her team (UC Davis) report a facile copper-catalyzed cycloaddition resulting in the immobilization of an iron-based homogeneous electrocatalyst on a glassycarbon electrode for CO2 to formate reduction. The investigated group 8 complex [Fe4N(CO)12] is an efficient electrocatalyst for CO2 reduction and retains activity upon functionalization and immobilization on the electrode surface. Their results are important because diminishing catalytic performance upon immobilization is a recurring problem in the development of functional formate-producing photoelectrochemical devices (DOI: 10.1021/acs.organomet.8b00396). Also concerned with iron-based, homogeneous electrocatalysis, a German collaboration led by the groups of Matthias Beller (Leibniz Institute for Catalysis), Ralf Ludwig and Robert Francke (Rostock University), and Michael Römelt (Ruhr University Bochum) provides mechanistic insights into iron(0)-catalyzed CO2 to CO reduction. In their report, a previously unknown Fe−Fe dimer is proposed to be the active species (DOI: 10.1021/acs.organomet.8b00517). Moving on to group 9, another report from Marc Robert’s Paris-based groupthis time teaming up with researchers from Hong Kong and Guangdong in Chinadescribes a mechanistic study of electrochemical CO2 to CO reduction by a molecular cobalt(II) catalyst: namely, the octahedral quaterpyridine complex [CoII(qpy)(H2O)]2+, employing an equatorially coordinating tetrapyridine chelate. The authors demonstrate that the electrocatalytic CO2 reduction in homogeneous solution proceeds via two different pathways at various potentials, with the exact mechanism depending on the concentration of the phenol proton source in solution (DOI: 10.1021/acs.organomet.8b00555). The French contribution by Yun Li and Marc Fontecave (Sorbonne University and University Paris-Saclay) reports on group 10 nickel dithiolene complexes that show unexpected electrocatalytic CO2 to formic acid reduction activity for the different stereoisomers. They suggest noncovalent interactions between the adsorbed nickel-based CO2 reduction catalyst and the applied mercury electrode to significantly enhance catalytic activity (DOI: 10. 1021/acs.organomet.8b00655). These results relate to Chang’s study reported in this Special Issue (DOI: 10.1021/acs. organomet.8b00308) and Kubiak’s previous work on nickel cyclam electrocatalysis.13 Furthermore, the Canadian group of Michael Wolf (University of British Colombia) reports improved electrocatalytic CO2 reduction by employing newly developed group 10 palladium complexes. The authors found that a pendant, positively charged onium ligand substituent of a pyridine-anchored bis(NHC) pincer complex mediates electrode kinetics and facilitates CO2 coordination at the catalytic center (DOI: 10.1021/acs.organomet.8b00649). The importance of stabilizing hydrogen-bonding interactions on electrocatalytic turnover is also demonstrated by a joint study on [Ni(cyclam)]2+reported by Eva Nichols and Chris Chang (UC Berkeley/Lawrence Berkeley National Laboratory and Howard Hughes Medical Institute). While Kubiak and coworkers reported the compound’s fast, efficient, and selective electrocatalytic reduction of CO2 to CO in 2015,13 Nichols and Chang’s simple, but creative, idea of utilizing a urea-based hydrogen-donor cocatalyst now adds a new chapter to this catalyst’s success story by “teaching an old dog new tricks”.

Speaking of new tricks, Daniel Nocera and his research team (Harvard University) describe continued studies on their famous iron hangman porphyrins. They adapt the beneficial hangman effect, observed for the hydrogen-evolution reaction, to advance strategies for electrocatalytic CO2 to CO reduction chemistry. In order to achieve this goal, they have a go at mediating the required proton-coupled electron transfer to the substrate by placing proton donor ligand functionalities with varying pKa values in the hangman cleft. These studies further highlight the benefits of controlling substrate binding within the secondary coordination sphere in the catalytic reduction of CO2 (DOI: 10.1021/acs.organomet.8b00334). Another exciting paper by the Nocera group in this issue describes progress in studying their heterogeneous cobalt-based O2-evolution catalyst featuring a cobalt-bound oxyl radical. They report their catalyst to be capable of full oxidative degradation of biomass (e.g., glucose or “Kraft lignin”) to CO2 in an aqueous environment; thus, they demonstrate potential biomass fuel cell applications. Nocera’s study supports the overall notion that metal-oxyl radicals in general, and their CoPi system in particular, accomplish efficient C−C bond cleavages under benign aqueous conditions. This property is indispensable for the advancement of catalysts capable of harvesting the full thermosdynamic potential of biomolecules (DOI: 10.1021/acs. organomet.8b00337). In Jules Verne’s “The Mysterious Island,” published in 1874, the engineer Cyrus Harding stated “I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable.” Almost 150 years later, H2 (from water) still is the biggest hope to one day be the environmentally friendly fuel of a future “hydrogen economy”. Accordingly, a Special Issue on electrocatalytic transformations could not be considered complete without contributions on the production of H2 (reduction of H+, preferably from water) as well as H2 oxidation. With respect to electrocatalytic H2 production and oxidation, it is remarkable that we still appear to have only one prevalent system, namely the bis(diphosphine) nickel complexes [Ni(PR2NR′2)2]2+,5 which continues to attract tremendous attention. Therefore, we are glad to feature a number of contributions from Pacific Northwest National Laboratory (PNNL) and its Center for Molecular Electrocatalysis on this topic. The Indian−American collaboration of Arnab Dutta (now Indian Institute of Technology) and Wendy Shaw (PNNL) studies derivatives of the parent nickel system and demonstrates an alternative and complementary chemical procedure for the turnover frequency (TOF) evaluation of moderately active and slow H2 oxidation catalysts. This is important because current state of the art electrochemical procedures do not allow for accurate TOF determination of slow catalysts, and the majority of active H2 oxidation catalysts are slow (TOFs ≤ 10 s−1). Who would have thought that the ubiquitous ferrocenium/ferrocene redox couple, in combination with NMR and UV/vis spectroscopic experiments, could be used to monitor and evaluate even the slowest H2 oxidation catalysts (DOI: 10.1021/acs.organomet.8b00580)? Eric Wiedner (PNNL) and coauthors (Villanova University) have been investigating nickel-based electrocatalytic H2 production, employing a rigid, tetradentate P4N2 phosphine derivative instead of the well-known bis(diphosphine) nickel 1183

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cyclometalated nickel species. The most notable feature of the newly prepared nickelacycles is an unusually low oxidation potential. Accordingly, these compounds can be air-oxidized, thereby presenting an opportunity for C(sp2)−C(sp2) and C− X bond forming reactions (DOI: 10.1021/acs.organomet. 8b00536). A Chinese collaborative work headed by Yu-Yan Li (China Pharmaceutical University), Xin-Yan Wu (East China University of Science & Technology), and Tian-Sheng Mei (Chinese Academy of Sciences, Shanghai) studies electrocatalytic alternatives for C−H functionalization that are environmentally friendly and will not require harsh chemical oxidants. In this Special Issue, the team communicates recent success in developing the first example of a one-compartment cell setup for electrochemical, palladium-catalyzed C(sp2)−H alkylation of arenes via anodic oxidation in aqueous solution (DOI: 10.1021/acs.organomet.8b00550). The Swedish team led by Mårten Ahlquist (KTH Royal Institute of Technology) computationally investigated the pHdependent performance of a ruthenium catalyst for water oxidation, originally developed by Llobet and co-workers (ICIQ). They calculate that the impressive rate improvement at higher pH is likely due to the involvement of a hydroxide ion in the initial O−O formation step, which is often proposed to be a challenging rate-determining step of water oxidation. The study also elucidated the importance of a hydrogenbonding network in stabilizing the hydroxide anion (vs. the radical) (DOI: 10.1021/acs.organomet.8b00544). Any successful and industrially relevant water-splitting device, however, is ultimately dependent on innovative storage technologies and materials, such as batteries. In a contribution from China by Xiaoyu Liu (Shanghai Polytechnic University), Yuyu Liu and Jiujun Zhang (Shanghai University), and their respective co-workers, the recent progress, challenges, and perspectives of earth-abundant, metal oxide based iron, cobalt, and nickel electrocatalysts for application in an interesting and developing storage technology, namely aqueous zinc−air batteries, is reviewed (DOI: 10.1021/acs.organomet.8b00508). In summary, this Special Issue features worldwide leading scientists presenting their current activities on electrocatalysis in organometallic chemistry, providing a fascinating overview of the most recent developments on small-molecule chemistry. Although our initial invitation to contribute to this Special Issue was kept general and purposefully broad, two main research themes emerged and are easily identified. The topics are concerned with two molecules of tremendous current interest and antithetical reputation, namely dihydrogen and carbon dioxide, which are irreversibly intertwined with current energy-related issues not unlike the novel Dr. Jekyll and Mr. Hyde (1886) that, ultimately, link its author Robert Louis Stevenson’s tale to his contemporary Jules Verne’s Mysterious Island novel (1874) and Harding’s belief in a robust hydrogen economy.

complex. The study presents a remarkably acid stable catalyst with an impressive TOF of >106 s−1. This is among the fastest described for any molecular catalyst, although this rate comes at the cost of an undesirable overpotential of 1.2 V (DOI: 10. 1021/acs.organomet.8b00548). Morris Bullock and colleagues (PNNL) extend their original works and describe an electrocatalytic study of iron-catalyzed H2 oxidation, supplemented by computational analyses, that demonstrates the importance of controlling outer-sphere proton movement, stabilizing H-bonding, and ring strain. They find that incorporation of an additional proton relay base into the outer coordination sphere of an iron hydride complex functionally mimics hydrogenase, thereby increasing the TOF of H2 oxidation (DOI: 10.1021/acs.organomet.8b00805). Jenny Yang and her group (UC Irvine) studied the pHdependent reactivity of water-soluble nickel catalysts in the aqueous hydrogen-evolution reaction. The sequential protonation events leading to H2 evolution were monitored by 31 1 P{ H} NMR spectroscopy, and the analysis of the reported data nicely illustrates how valuable these mechanistic studies can be to understanding the functional pH range of hydrogenevolution electrocatalysts proceeding through metal hydride intermediates (DOI: 10.1021/acs.organomet.8b00558). The British−Austrian−German team around Benno Bildstein (University of Innsbruck), Erwin Reisner (University of Cambridge), and Rainer Winter (University of Konstanz) prepared and investigated novel trimetallic complexes with a central tetraazenido-cyclopentadienyl cobalt unit. The compounds are functionalized with peripheral metallocenyl substituents and show that the all-cobalt-comprising complex catalyzes electrochemical proton reduction at modest overpotential (DOI: 10.1021/acs.organomet.8b00681). James Blakemore and co-workers at the University of Kansas present their investigations of a pentamethylcyclopentadienyl (Cp*) rhodium complex bearing a hybrid phosphine-imine chelate in an effort to unveil the role of the bidentate donor in hydride formation and potentially H2 production. Surprisingly, and in contrast to the electrocatalytically active Cp*Rh species supported by diimine ligands, their rhodium hydride derivative is resistant to protonation and does not engage in H 2 production (DOI: 10.1021/acs.organomet.8b00551). Work from Singapore and India, under the tutelage of Han Sen Soo, involves the synthesis of new electron-rich nickel and cobalt complexes with derivatives of the well-known tetraamido macrocyclic TAML ligand system and investigates the potential catalytic applications for the production of H2 from water. Initially, the cobalt TAML complex appeared to be active for electrocatalytic H2 evolution, but ultimatelyas often happens in homogeneous catalysisdetailed studies revealed that electrodeposited cobalt(0) nanoparticles were responsible for the observed catalysis. This topic has become increasingly important with the development of functionalized electrode materials (DOI: 10.1021/acs.organomet.9b00032). Research presented by Yulia Budnikova and co-workers (Russian Academy of Sciences) aims at testing nickel complexes for possible applications in C−H bond activation chemistry. Their study focuses on nickelacycles and their possible application in an electrocatalytic cycle for the generation of products with new carbon−carbon and carbon−heteroatom bonds. The synthetic, crystallographic, and electrochemical study is supported by EPR spectroscopy and DFT computational analyses, and it provides new information on the redox properties and reactivity of

Christophe Werlé† Karsten Meyer*,‡ †

Max-Planck-Institute for Chemical Energy Conversion, Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany ‡ Friedrich-Alexander-University Erlangen-Nürnberg, Department of Chemistry and Pharmacy, Inorganic Chemistry, Egerlandstraße 1, D-91058 Erlangen, Germany 1184

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AUTHOR INFORMATION

engineered ligand environments. Benchmarks of the Meyer research work comprise the activation, cleavage, and multiple-bond metathesis of carbon dioxide at uranium complexes and the synthesis of reactive metal peroxo, imido, and nitrido complexes for the functionalization of organic molecules via atom and group transfer chemistry. Highlights include the identification of a previously unknown U(II) oxidation state and the f-element-based electrocatalytic reduction of water for the production of dihydrogen, thus opening new avenues to uranium and lanthanide reactivity.

Corresponding Author

*E-mail for K.M.: [email protected]. ORCID

Christophe Werlé: 0000-0002-2174-2148 Karsten Meyer: 0000-0002-7844-2998 Notes

Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.

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Biographies

REFERENCES

(1) Cracknell, J. A.; Vincent, K. A.; Armstrong, F. A. Enzymes as Working or Inspirational Electrocatalysts for Fuel Cells and Electrolysis. Chem. Rev. 2008, 108, 2439−2461. (2) Habibzadeh, F.; Miller, S. L.; Hamann, T. W.; Smith, M. R., III Homogeneous Electrocatalytic Oxidation of Ammonia to N2 under Mild Conditions. Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/ pnas.1813368116. (3) (a) Nichols, E. M.; Gallagher, J. J.; Liu, C.; Su, Y.; Resasco, J.; Yu, Y.; Sun, Y.; Yang, P.; Chang, M. C.; Chang, C. J. Hybrid Bioinorganic Approach to Solar-to-Chemical Conversion. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 11461−11466. (b) Hall, D. O.; Rao, K. Photosynthesis, 5th ed.; Cambridge University Press: Cambridge, U.K., 1994. (4) Schilter, D.; Camara, J. M.; Huynh, M. T.; Hammes-Schiffer, S.; Rauchfuss, T. B. Hydrogenase Enzymes and Their Synthetic Models: The Role of Metal Hydrides. Chem. Rev. 2016, 116, 8693−8749. (5) Helm, M. L.; Stewart, M. P.; Bullock, R. M.; DuBois, M. R.; DuBois, D. L. A Synthetic Nickel Electrocatalyst with a Turnover Frequency above 100,000 s−1 for H2 Production. Science 2011, 333, 863−866. (6) Can, M.; Armstrong, F. A.; Ragsdale, S. W. Structure, Function, and Mechanism of the Nickel Metalloenzymes, Co Dehydrogenase, and Acetyl-Coa Synthase. Chem. Rev. 2014, 114, 4149−4174. (7) Chaudhary, Y. S.; Woolerton, T. W.; Allen, C. S.; Warner, J. H.; Pierce, E.; Ragsdale, S. W.; Armstrong, F. A. Visible Light-Driven CO2 Reduction by Enzyme Coupled CdS Nanocrystals. Chem. Commun. 2012, 48, 58−60. (8) (a) Beley, M.; Collin, J. P.; Ruppert, R.; Sauvage, J. P. Electrocatalytic Reduction of Carbon Dioxide by Nickel Cyclam2+ in Water: Study of the Factors Affecting the Efficiency and the Selectivity of the Process. J. Am. Chem. Soc. 1986, 108, 7461−7467. (b) Costentin, C.; Drouet, S.; Robert, M.; Saveant, J. M. A Local Proton Source Enhances CO2 Electroreduction to CO by a Molecular Fe Catalyst. Science 2012, 338, 90−94. (9) Horn, E. J.; Rosen, B. R.; Baran, P. S. Synthetic Organic Electrochemistry: An Enabling and Innately Sustainable Method. ACS Cent. Sci. 2016, 2, 302−308. (10) (a) Kolbe, H. Zersetzung der Valeriansäure durch den elektrischen Strom. Annalen der Chemie und Pharmacie 1848, 64, 339−341. (b) Kolbe, H. Untersuchungen über die Elektrolyse organischer Verbindungen. Annalen der Chemie und Pharmacie 1849, 69, 257−294. (11) Corey, E. J.; Sauers, R. R. The Synthesis of Pentacyclosqualene (8,8′-Cycloönocerene) and the A- and B-Onoceradienes. J. Am. Chem. Soc. 1959, 81, 1739−1743. (12) Horn, E. J.; Rosen, B. R.; Chen, Y.; Tang, J.; Chen, K.; Eastgate, M. D.; Baran, P. S. Scalable and Sustainable Electrochemical Allylic C−H Oxidation. Nature 2016, 533, 77. (13) Froehlich, J. D.; Kubiak, C. P. The Homogeneous Reduction of CO2 by [Ni(Cyclam)]+: Increased Catalytic Rates with the Addition of a CO Scavenger. J. Am. Chem. Soc. 2015, 137, 3565−3573.

Christophe Werlé serves currently as the group leader of “organometallic electrocatalysis” in the department of molecular catalysis at the Max-Planck-Institute for chemical energy conversion. After obtaining his doctoral degree from the University of Strasbourg in 2014 for his work on the experimental and theoretical study of noncovalent interactions in the field of organometallic chemistry, he joined in October 2014 the group of Prof. Dr. Alois Fürstner at the Max-Planck-Institut für Kohlenforschung. His research in the field of rhodium and gold catalysis led to the isolation and structural characterization of pertinent catalytic intermediates that were so far found to be too reactive for direct inspection. Then, in September 2016 he joined the group of Prof. Dr. Karsten Meyer at the FriedrichAlexander-Universität Erlangen-Nürnberg, where he worked on the design and synthesis of new anchoring ligands and their application in the uranium-mediated electrocatalytic water oxidation reaction. In September 2017 he joined the group of Prof. Dr. Walter Leitner, where he is currently actively working on the transition-metalcatalyzed electrochemical reduction of carbon dioxide in various value-added chemicals.

The Meyer research program is focused on the activation of small molecules of biological and industrial interest using redox-active uranium and first-row transition-metal complexes in molecularly 1185

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