Electrochemical studies of the preparation and one-electron reduction of half-sandwich cobalt-arene cations

1984 ◽  
Vol 3 (12) ◽  
pp. 1910-1911 ◽  
Author(s):  
Joseph Edwin ◽  
William E. Geiger
Keyword(s):  
Electrochemical Studies ◽  
Electron Reduction ◽  
Half Sandwich

Organophosphazenes. 25. The synthesis and electrochemistry of the dicobalt hexacarbonyl complexes of phenylethynylcyclophosphazenes

2002 ◽  
Vol 80 (11) ◽  
pp. 1393-1397 ◽  
Author(s):  
Maneesh Bahadur ◽  
Christopher W Allen ◽  
William E Geiger ◽  
Adam Bridges
Keyword(s):  
Spin Density ◽  
Nmr Spectra ◽  
Esr Spectra ◽  
Radical Anions ◽  
Electrochemical Studies ◽  
Unpaired Spin Density ◽  
Unpaired Spin ◽  
Electron Reduction ◽  
Dicobalt Hexacarbonyl

The syntheses of the dicobalt hexacarbonyl complexes, N3P3F6-n(C[Formula: see text]CPhCo2(CO)6)n (n = 1 (3), n = 2 (4)), is reported. The introduction of the organometallic fragment allows for simplification of the NMR spectra and separation of the isomers of the disubstituted (4) derivatives. Electrochemical studies show that 3 undergoes a reversible one-electron reduction. At 233 K, the geminal isomer of 4 undergoes two separate reversible one-electron reductions. The ESR spectra of the radical anions of 3 and 4 have been obtained and show the absence of delocalization of unpaired spin density from the organometallic cluster to the phosphazene.Key words: cyclophosphazenes, cobalt–alkyne clusters, electrochemistry, ESR.

Electrochemical Studies of Organotitanium Nitrogen Fixation Systems

1973 ◽  
Vol 51 (6) ◽  
pp. 815-820 ◽  
Author(s):  
T. Chivers ◽  
E. D. Ibrahim
Keyword(s):  
Cyclic Voltammetry ◽  
Nitrogen Fixation ◽  
Electrochemical Reduction ◽  
Argon Atmosphere ◽  
Electrochemical Studies ◽  
Controlled Potential Electrolysis ◽  
Controlled Potential ◽  
Electron Reduction ◽  
The One ◽  
Ether Solvents

The electrochemical reduction of compounds of the type (π-Cp)2Ti(R)Cl (R = Cl, CH3, C6H5, C5F5, OTiCl(π-Cp)2) in ether solvents has been studied using the techniques of polarography, controlled potential electrolysis, and cyclic voltammetry. The one-electron reduction products, presumably (π-Cp)2TiR (R = CH3, C6F5), are initially green in tetrahydrofuran but, in a dinitrogen or argon atmosphere, they form intensely blue solutions which result from the reaction of (π-Cp)2TiR with tetrahydrofuran solvent.

scholarly journals A Binuclear Cobalt Complex for Molecular CO2 Electrocatalysis

2021 ◽  
Author(s):  
Antoine Bohn ◽  
Juan José Moreno ◽  
Pierre Thuéry ◽  
Marc Robert ◽  
Orestes Rivada Wheelaghan
Keyword(s):  
Carbon Dioxide ◽  
Carbon Monoxide ◽  
Saturated Calomel Electrode ◽  
Cobalt Complex ◽  
Reduction Process ◽  
Inert Atmosphere ◽  
Electrochemical Studies ◽  
Electron Reduction ◽  
Carbon Dioxide Co2 ◽  
Reduction Of Co2

A pyrazole–based ligand substituted with terpyridine groups at the 3 and 5positions has been synthesized to form the dinuclear cobalt complex 1, that electrocatalytically reduces carbon dioxide (CO2) to carbon monoxide (CO) in the presence of Brønsted acids in DMF. Chemical, electrochemical and UV–vis spectro–electrochemical studies under inert atmosphere indicate a single 2 electron reduction process of complex 1 at first, followed by a 1 electron reduction at the ligand. Infrared spectro–electrochemical studies under CO2 and CO atmosphere allowed us to identify a reduced CO–containing dicobalt complex which results from the electroreduction of CO2. In the presence of trifluoroethanol (TFE), electrocatalytic studies revealed single–site mechanism with up to 94 % selectivity towards CO formation when 1.47 M TFE were present, at –1.35 V vs Saturated Calomel Electrode in DMF (0.39 V overpotential). The low faradaic efficiencies obtained (<50%) are attributed to the generation of CO–containing species formed during the electrocatalytic process, which inhibit the reduction of CO2.

scholarly journals Remote Oxidative Activation of a [Cp*Rh] Monohydride

2021 ◽  
Author(s):  
Emily Boyd ◽  
Julie Hopkins Leseberg ◽  
Emma Cosner ◽  
Davide Lionetti ◽  
Wade Henke ◽  
...  
Keyword(s):  
Electrochemical Oxidation ◽  
Epr Spectroscopy ◽  
Redox Activity ◽  
Electrochemical Studies ◽  
Attractive Feature ◽  
Nmr Studies ◽  
Reactivity Pattern ◽  
Oxidative Activation ◽  
Half Sandwich

Half-sandwich rhodium monohydrides are often proposed as intermediates in catalysis, but little is known regarding the redox-induced reactivity accessible to these species. Here, the κ2-bis-diphenylphosphinoferrocene (dppf) ligand has been used to explore the reactivity that can be induced when a [Cp*Rh] monohydride undergoes remote (dppf-centered) oxidation by 1e–. Chemical and electrochemical studies showed that one-electron redox chemistry is accessible to Cp*Rh(dppf), including a unique quasi-reversible RhII/I process at –0.96 V vs. ferrocenium/ferrocene (Fc+/0). This redox manifold was confirmed by isolation of an uncommon Rh(II) species that was characterized by EPR spectroscopy. Protonation of Cp*Rh(dppf) with anilinium triflate yielded an isolable and inert monohydride, and this species was found to undergo a quasireversible electrochemical oxidation at +0.41 V vs Fc+/0 that corresponds to iron-centered oxidation in the dppf backbone. Thermochemical analysis predicts that this dppf-centered oxidation drives a dramatic increase in acidity of the Rh–H moiety by 23 pKa units, a reactivity pattern confirmed by in situ 1H NMR studies. Taken together, these results show that remote oxidation can effectively induce M–H activation and suggest that ligand-centered redox activity could be an attractive feature for design of new systems relying on hydride intermediates.

A Pyridinic Fe-N4 Macrocycle Effectively Models the Active Sites in Fe/N-Doped Carbon Electrocatalysts

2020 ◽  
Author(s):  
Travis Marshall-Roth ◽  
Nicole J. Libretto ◽  
Alexandra T. Wrobel ◽  
Kevin Anderton ◽  
Nathan D. Ricke ◽  
...  
Keyword(s):  
Oxygen Reduction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Reduction Reaction ◽  
Iron Phthalocyanine ◽  
Electrochemical Studies ◽  
Onset Potential ◽  
Nitrogen Doped Carbon ◽  
Iron Active Sites

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum in fuel cells, but their active site structures are poorly understood. A leading postulate is that iron active sites in this class of materials exist in an Fe-N<sub>4</sub> pyridinic ligation environment. Yet, molecular Fe-based catalysts for the oxygen reduction reaction (ORR) generally feature pyrrolic coordination and pyridinic Fe-N<sub>4</sub> catalysts are, to the best of our knowledge, non-existent. We report the synthesis and characterization of a molecular pyridinic hexaazacyclophane macrocycle, (phen<sub>2</sub>N<sub>2</sub>)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for oxygen reduction to a prototypical Fe-N-C material, as well as iron phthalocyanine, (Pc)Fe, and iron octaethylporphyrin, (OEP)Fe, prototypical pyrrolic iron macrocycles. N 1s XPS signatures for coordinated N atoms in (phen<sub>2</sub>N<sub>2</sub>)Fe are positively shifted relative to (Pc)Fe and (OEP)Fe, and overlay with those of Fe-N-C. Likewise, spectroscopic XAS signatures of (phen<sub>2</sub>N<sub>2</sub>)Fe are distinct from those of both (Pc)Fe and (OEP)Fe, and are remarkably similar to those of Fe-N-C with compressed Fe–N bond lengths of 1.97 Å in (phen<sub>2</sub>N<sub>2</sub>)Fe that are close to the average 1.94 Å length in Fe-N-C. Electrochemical studies establish that both (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe have relatively high Fe(III/II) potentials at ~0.6 V, ~300 mV positive of (OEP)Fe. The ORR onset potential is found to directly correlate with the Fe(III/II) potential leading to a ~300 mV positive shift in the onset of ORR for (Pc)Fe and (phen<sub>2</sub>N<sub>2</sub>)Fe relative to (OEP)Fe. Consequently, the ORR onset for (phen<sub>2</sub>N<sub>2</sub>)Fe and (Pc)Fe is within 150 mV of Fe-N-C. Unlike (OEP)Fe and (Pc)Fe, (phen<sub>2</sub>N<sub>2</sub>)Fe displays excellent selectivity for 4-electron ORR with <4% maximum H<sub>2</sub>O<sub>2</sub> production, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data establish (phen<sub>2</sub>N<sub>2</sub>)Fe as a pyridinic iron macrocycle that effectively models Fe-N-C active sites, thereby providing a rich molecular platform for understanding this important class of catalytic materials.<p><b></b></p>

Half- Sandwich cyclopentadienylruthenium(II) Complexes: A New Antimalarial Chemotype

2020 ◽  
Author(s):  
Sofia Alexandra Milheiro ◽  
Joana Gonçalves ◽  
Ricardo Lopes ◽  
Margarida Madureira ◽  
Lis Lobo ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Blood Stage ◽  
Nuclear Accumulation ◽  
Selective Absorption ◽  
Asexual Parasite ◽  
Single Digit ◽  
Liver Stage ◽  
Dual Stage ◽  
Fluorescent Compounds ◽  
Half Sandwich

<p><a>A small library of “half-sandwich” cyclopentadienylruthenium(II) compounds of general formula [(</a>η<sup>5</sup>-C<sub>5</sub>R<sub>5</sub>)Ru(PPh<sub>3</sub>)(N-N)][PF<sub>6</sub>], a scaffold hitherto unfeatured in the toolbox of antiplasmodials, was screened for activity against the blood stage of CQ-sensitive 3D7-GFP, CQ-resistant Dd2 and artemisinin-resistant IPC5202 <i>Plasmodium falciparum</i> strains, and the liver stage of <i>P. berghei</i>. The best performing compounds displayed dual-stage activity, with single-digit nM IC<sub>50</sub> values against blood stage malaria parasites, nM activity against liver stage parasites, and residual cytotoxicity against mammalian cells (HepG2, Huh7). Parasitic absorption/distribution of 7-nitrobenzoxadiazole-appended fluorescent compounds <b>Ru4</b> and <b>Ru5</b> was investigated by confocal fluorescence microscopy, revealing parasite-selective absorption in infected erythrocytes and nuclear accumulation of both compounds. The lead compound <b>Ru2</b> impaired asexual parasite differentiation, exhibiting fast parasiticidal activity against both ring and trophozoite stages of a synchronized <i>P. falciparum</i> 3D7 strain. These results point to cyclopentadienylruthenium(II) complexes as a highly promising chemotype for the development of dual-stage antiplasmodials.</p>

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

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