Source Of Hydrogen Atoms Research Articles

Photo-induced carboxylation of C(sp2)−S bonds in aryl thiols and derivatives with CO2

Aryl thiols have proven to be a useful class of electron donors and hydrogen atom sources in photochemical processes. However, the direct activation and functionalization of C(sp2)–S bonds in aryl thiols remains elusive in the field of photochemistry. Herein, a photochemical carboxylation of C(sp2)–S bonds in aryl thiols with CO2 is reported, providing a synthetic route to important aryl carboxylic acids. Moreover, different kinds of aryl thiol derivatives, benzeneselenol and diphenyl diselenide also show moderate-to-high reactivity in this transformation. Mechanistic studies, including DFT calculations, suggest that the in situ generated carbon dioxide radical anion (CO2•−) and disulfide might be the key intermediates, which undergo radical substitution to yield products. This reaction features mild and catalyst-free conditions, good functional group tolerance and wide substrate scope. Furthermore, the efficient degradation of polyphenylene sulfide highlights the usefulness of this methodology.

Organoelectrocatalytic cyclopropanation of alkenyl trifluoroborates with methylene compounds

Cyclopropanes are not only privileged motifs in many natural products, agrochemicals, and pharmaceuticals, but also highly versatile intermediates in synthetic chemistry. As such, great effort has been devoted to the cyclopropane construction. However, novel catalytic methods for cyclopropanation with two abundant substrates, mild conditions, high functional group tolerance, and broad scope are still highly desirable. Herein, we report an intermolecular electrocatalytic cyclopropanation of alkenyl trifluoroborates with methylene compounds. The reaction uses simple diphenyl sulfide as the electrocatalyst under base-free conditions. And thus, a broad scope of various methylene compounds as well as vinyltrifluoroborates is demonstrated, including styrenyl, 1,3-dienyl, fluorosulfonyl, and base-sensitive substrates. Preliminary mechanistic studies are presented, revealing the critical role of the boryl substituent to facilitate the desired pathway and the role of water as the hydrogen atom source.

Direct observation of nanometer size hydride precipitations in superconducting niobium

Superconducting niobium serves as a key enabling material for superconducting radio frequency (SRF) technology as well as quantum computing devices. Niobium has a high propensity for the uptake of hydrogen. At room temperature, hydrogen commonly occupies tetragonal sites in the Nb lattice as the metal (M)–gas (H) phase. When the temperature is decreased, however, a solid solution of Nb-H begins to precipitate. In this study, we show the first identified topographical features associated with nanometer-size hydride phase (Nb1−xHx) precipitates on the surface of the metallic superconducting niobium using cryogenic-atomic force microscopy (AFM). Further, high energy grazing incidence X-ray diffraction reveals information regarding the structure and stoichiometry of these precipitates. Finally, through time-of-flight secondary ion mass spectroscopy (ToF-SIMS), we locate atomic hydrogen sources near the top surface. This systematic study clarifies nanometer scale hydrides precipitated on the surface of the SRF Nb cavity that exhibit performance degradation at a high accelerating field regime.

Insight into the mechanism of H2O promoted CaCO3 decomposition in CO2 atmosphere

Calcium looping is one of the most promising CO2 capture technology. The flus gas during the calcination stage of the calcium looping contains both CO2 and H2O. However, the effect of H2O on the decomposition of carbonation in the CO2 atmosphere remains inconclusive. This study employed the Reactive Force Field molecular dynamics (ReaxFF-MD) simulations to investigate the influence of H2O on the decomposition of calcium carbonate in a CO2 atmosphere. The TGA experiments demonstrated that H2O increases the decomposition rate of calcium carbonate and also reduces the reaction temperature. Subsequently, the effects of varying CO2 and H2O concentrations on the decomposition of calcium carbonate were examined using ReaxFF-MD simulations. The simulation results for calcium carbonate decomposition, with the addition of CO2 and H2O, aligned with the experimental trends, verifying the reliability of the models. By tracking and labeling carbon, oxygen and hydrogen atom sources in the simulation, the decomposition, carbonation and hydrolysis reaction network for the CaCO3 decomposition in CO2 atmosphere was systematically constructed. Analysis of the chemical reactions and atomic distribution indicated that H2O primarily facilitates calcium carbonate decomposition by generating HCO3− through surface hydrolysis, which reduces the activation energy of the reaction. Moreover, the hydroxyl groups formed by hydrolysis compete with atmospheric CO2 for active sites on CaO, further inhibiting the carbonation reaction and increasing the calcination rate.

Understanding the Reducibility of CeO2 Surfaces by Proton-Electron Transfer from CpCr(CO)3H.

CeO2 is a popular material in heterogeneous catalysis, molecular sensors, and electronics and owes many of its special properties to the redox activity of Ce, present as both Ce3+ and Ce4+. However, the reduction of CeO2 with H2 (thought to occur through proton-electron transfer (PET) giving Ce3+ and new OH bonds) is poorly understood due to the high reduction temperatures necessary and the ill-defined nature of the hydrogen atom sources typically used. We have previously shown that transition-metal hydrides with weak M-H bonds react with reducible metal oxides at room temperature by PET. Here, we show that CpCr(CO)3H (1) transfers protons and electrons to CeO2 due to its weak Cr-H bond. We can titrate CeO2 with 1 and measure not only the number of surface Ce3+ sites formed (in agreement with X-ray absorption spectroscopy) but also the lower limit of the hydrogen atom adsorption free energy (HAFE). The results match the extent of reduction achieved from H2 treatment and hydrogen spillover on CeO2 in a wide range of applications.

Sprayed Oil-Water Microdroplets as a Hydrogen Source.

Liquid water provides the largest hydrogen reservoir on the earth's surface. Direct utilization of water as a source of hydrogen atoms and molecules is fundamental to the evolution of the ecosystem and industry. However, liquid water is an unfavorable electron donor for forming these hydrogen species owing to its redox inertness. We report oil-mediated electron extraction from water microdroplets, which is easily achieved by ultrasonically spraying an oil-water emulsion. Based on charge measurement and electron paramagnetic resonance spectroscopy, contact electrification between oil and a water microdroplet is demonstrated to be the origin of electron extraction from water molecules. This contact electrification results in enhanced charge separation and subsequent mutual neutralization, which enables a ∼13-fold increase of charge carriers in comparison with an ultrapure water spray, leading to a ∼16-fold increase of spray-sourced hydrogen that can hydrogenate CO2 to selectively produce CO. These findings emphasize the potential of charge separation enabled by spraying an emulsion of liquid water and a hydrophobic liquid in driving hydrogenation reactions.

Ti(III)-Catalyzed Anti-Markovnikov Reduction of Epoxides with Borohydride.

We have developed a Ti catalyst that carries out the anti-Markovnikov reduction of a wide range of epoxides; [BH4]- is used as both the electron and the hydrogen atom source. It requires only mild conditions and accommodates a broad range of epoxide substrates. The Ti catalyst is readily available and is environmentally friendly.

Utilization of Magonia pubescens extracts in the synthesis of rhodium NPs on Fe3O4@MgO support: A novel catalyst for 4-nitrophenol hydrogenation

This study reports the development of three distinct nanoparticulate catalysts, each comprising a biosynthesized Fe3O4 nanoparticle magnetic core with an average diameter of 17 nm, showcasing superparamagnetic behavior. This magnetic core was further encased in a spherical magnesium oxide (MgO) layer through a bio-inspired strategy, leading to the Fe3O4@MgO support structure. Rhodium (Rh) nanoparticles, with diameters between 1.0 and 1.5 nm, were then fabricated to act as the main catalytic entities. These were subsequently affixed to the Fe3O4@MgO support, yielding Fe3O4@MgO-Rh, using three distinct methodologies. Remarkably, the bio-inspired processes employed for the creation of Fe3O4@MgO-Rh harnessed the infusion and extract from Magonia pubescens A St. Hil leaves, colloquially termed “Timbó”. These natural extracts played dual roles as reducing and stabilizing agents during the catalyst generation, leading to three variants: CI, CW, and CS. Comprehensive characterization of these catalysts was achieved using XPS, TEM, EDS, and VSM techniques. The ensuing evaluation involved the hydrogenation of 4-nitrophenol, which served to assess the efficiency and resilience of the bio-inspired catalysts vis-à-vis conventionally-produced counterparts. Notably, under benign conditions of a molecular H2 atmosphere (an ecologically sound hydrogen atom source) and moderate temperatures (60 °C), conversion rates exceeding 97 % were consistently observed for the substrate within a time frame of 0 to 15 min. For a more granular comparison of efficiency among the rhodium-centric catalysts, Turnover Frequency (TOF) and Total Turnover Number (TTON) computations were undertaken. Herein, the CI catalyst, originating from infusion, displayed a TTON value of 1263.24, underscoring its preeminence in 4-NF hydrogenation reactions. This was closely trailed by the CS catalyst, which boasted a TTON of 873.63, synthesized with a commercial surfactant.

Enthalpy of the N+ + H2 → NH+ + H Reaction—Experimental Study of the Reverse Process

The formation of nitrogen hydrides in the interstellar medium is initiated by the nearly thermoneutral reaction of N+ + H2 → NH+ + H. Here, we experimentally determine the enthalpy of this reaction using the principle of detailed balance from a measurement of the rate coefficient of the reverse reaction NH+ + H → N+ + H2. The measurements were carried out in a linear radiofrequency 22-pole trap combined with an effusive beam source of atomic hydrogen at temperatures between 10 and 100 K. The resulting ground-state energy difference (or reaction enthalpy at 0 K) of ΔE 0 = (18 ± 4) meV confirms that there are no significant energy barriers on the reaction path.

Photoinduced NiH Catalysis with Trialkylamines for the Stereodivergent Transfer Semi-Hydrogenation of Alkynes.

We report a selectivity-switchable nickel hydride-catalyzed methodology that enables the stereocontrolled semi-reduction of internal alkynes to E- or Z-alkenes under very mild conditions. The proposed transfer semi-hydrogenation process involves the use of a dual nickel/photoredox catalytic system and triethylamine, not only as a sacrificial reductant, but also as a source of hydrogen atoms. Mechanistic studies revealed a pathway involving photo-induced generation of nickel hydride, syn-hydronickelation of alkyne, and alkenylnickel isomerization as key steps. Remarkably, mechanistic experiments indicate that the control of the stereoselectivity is not ensuing from a post-reduction alkene photoisomerization under our conditions. Instead, we demonstrate that the stereoselectivity of the reaction is dependent on the rate of a final protonolysis step which can be tuned by adjusting the pKa of an alcohol additive.

Radical‐Mediated Hydroperfluoroalkylation of Unactivated Alkenes

AbstractThe direct hydroperfluoroalkylation of a wide range of unactivated alkenes has been achieved at room temperature with readily available iodoperfluoroalkanes using 4‐tert‐butylcatechol as a source of hydrogen atom and triethylborane. The hydrotrifluoromethylation could also be achieved under these conditions using gaseous trifluoromethyl iodide. An experimentally simple two‐step, one‐pot hydrotrifluoromethylation process using the easy‐to‐use trifluoromethanesulfonyl chloride as the source of trifluoromethyl radicals has also been developed. Using these two approaches, a broad range of substrates, including isoprenoid natural products, were efficiently derivatized.

Merging decatungstate photocatalysis and copper‐catalyzed azide‐alkyne cycloaddition reaction for the formation of 1,2,3‐triazoles in water†

Merging photoredox and catalysis by transition metals, coined as metallaphotoredox catalysis, proved to be an excellent new platform for the development of new synthetic strategies for the formation of carbon–carbon and carbon‐heteroatom bonds. Herein, we report a dual catalytic system that has been successfully developed for the azide‐alkyne ligation process to yield 1,4‐disubstituted‐1,2,3‐triazoles. It consists of merging the decatungstate anion [W10O32]4−‐photocatalyzed hydrogen atom transfer from ethanol as a source of hydrogen atom abstraction to produce the one‐electron‐reduced form H+[W10O32]5−, which reduces Cu(II) precursor into Cu(I) starting then the copper‐catalyzed azide‐alkyne cycloaddition reaction (CuAAC). The resulting bifunctional H+[W10O32]5−/Cu catalytic system operates efficiently in an environmentally benign water–ethanol solvent mixture as reaction medium, resulting in the regioselective formation of 1,4‐disubstituted‐1,2,3‐triazole derivatives, with high yields up to 99% and large substrate application scope under mild conditions. This dual catalytic approach has proven to function under sunlight exposition too with recovery and reuse of the catalytic system for several times.

Mechanistic Studies of the Electrocatalytic Carbon–Bromine Cleavage and the Hydrogen Atom Incorporation from 1,1,1,3,3,3-Hexaflouroisopropanol

Electrochemical dehalogenation of polyhalogenated compounds is an inefficient process as the working electrode is passivated by the deposition of short-chain polymers that form during the early stages of electrolysis. Herein, we report the use of 1, 1, 1, 3, 3, 3-hexaflouroisopropanol (HFIP) as an efficient reagent to control C–H formation over the radical association. Debromination of 1,6-dibromohexane was examined in the presence of Ni(II) salen and HFIP as the electrocatalyst and hydrogen atom source, respectively. Electrolysis of 10 mM 1,6-dibromohexane and 2 mM Ni(II) salen in the absence of HFIP yields 50% unreacted 1,6-dibromohexane and ∼40% unaccounted for starting material, whereas electrolysis with 50 mM HFIP affords 65% n-hexane. The mechanism of hydrogen atom incorporation was examined via deuterium incorporation coupled with high-resolution mass spectrometry, and density functional theory (DFT) calculations. Deuterium incorporation analysis revealed that the hydrogen atom originated from the secondary carbon of HFIP. DFT calculations showed that the deprotonation of hydroxyl moiety of HFIP, prior to the hydrogen atom transfer, is a key step for C–H formation. The scope of electrochemical dehalogenation was examined by electrolysis of 10 halogenated compounds. Our results indicate that through the use of HFIP, the formation of short-chain polymers is no longer observed, and monomer formation is the dominant product.

(Energy Technology Division Walter van Schalkwijk Award in Sustainable Energy Technology Address) Low Temperature Water Electrolysis as a Near Term Enabler in Climate Change Mitigation

Generating hydrogen from renewable production methods such as water electrolysis is fundamental to meeting decarbonization goals and mitigating climate change. Regardless of the end market split for hydrogen in ground transportation applications, hydrogen is the major feedstock for industrial chemicals such as ammonia and methanol. The only way to make these processes sustainable is to eliminate carbon dioxide emissions from production of the hydrogen feedstock. Currently, over 95% of this hydrogen is generated from natural gas and other fossil fuels, producing roughly 9 g CO2/g H2. A combination of technologies such as natural gas reforming with carbon capture, utilization and sequestration (CCUS) and water splitting via electrolysis therefore need to be deployed as quickly as possible. In addition, any scheme to convert carbon dioxide to useful chemicals requires a renewable source of hydrogen atoms. So to address both curtailment of ongoing emissions and mitigation of existing CO2 waste streams, renewable hydrogen is a lynchpin for success.Low temperature electrolysis has commercially deployed for decades, making it one of the only water splitting technologies likely to make an impact in the next 5-10 years. Both liquid alkaline electrolyzers (or alkaline water electrolyzers, AWE) and proton exchange membrane water electrolyzers (PEMWE) have been deployed at >10 MW scale, and many companies are actively working to scale manufacturing to gigawatt capacity. While 2050 goals will likely involve implementation of a broader portfolio of technologies, scaling deployment of existing carbon neutral hydrogen technologies provides the greatest long term benefit by reducing overall emissions earlier. We therefore cannot let “perfect [become] the enemy of good”[1] in terms of waiting for the most efficient, lowest cost solution. At the same time, there are significant improvements that can be made in both AWE and PEMWE products, through advanced materials, processes, and automation. The PEMWE technology in particular can leverage much of the investment in PEM fuel cell research and development, although understanding of electrolysis specific materials and processes in ongoing. This talk will focus on the relationships between material research, process development, and understanding of degradation mechanisms in commercializing reliable technology, and the importance of academia, national labs, and industry to work together in this effort. [1] Commonly attributed to Voltaire, and others.

Light-Assisted Semi-Hydrogenation of 1,3-Butadiene with Water.

Sustainable processes for semi-hydrogenation of alkynes/alkadienes impurities in alkenes feedstocks are in great demand in industry as the utilization of excessive hydrogen, high temperature and unsatisfactory alkenes selectivity of the current thermo-catalytic route, however, their development is still challenging. Herein, we innovate a light-assisted semi-hydrogenation process in gas-feed fixed bed reactor, with water as hydrogen atom source by in situ photocatalysis. Using Pd/TiO2 as model catalyst, this process shows an excellent catalytic performance for the semi-hydrogenation of 1,3-butadiene, with 100 % of butenes selectivity at ≈99 % of conversion over 180 h of reaction at ambient temperature driven by 66 mW cm-2 of irradiation intensity. This light-driven, H2 -free, ambient temperature semi-hydrogenation process, with superior performance to that of thermocatalytic route, shows attractive to bring an evolution in industrial hydrogenation technology to an economical and safe way.

Light‐Assisted Semi‐Hydrogenation of 1,3‐Butadiene with Water

AbstractSustainable processes for semi‐hydrogenation of alkynes/alkadienes impurities in alkenes feedstocks are in great demand in industry as the utilization of excessive hydrogen, high temperature and unsatisfactory alkenes selectivity of the current thermo‐catalytic route, however, their development is still challenging. Herein, we innovate a light‐assisted semi‐hydrogenation process in gas‐feed fixed bed reactor, with water as hydrogen atom source by in situ photocatalysis. Using Pd/TiO2 as model catalyst, this process shows an excellent catalytic performance for the semi‐hydrogenation of 1,3‐butadiene, with 100 % of butenes selectivity at ≈99 % of conversion over 180 h of reaction at ambient temperature driven by 66 mW cm−2 of irradiation intensity. This light‐driven, H2‐free, ambient temperature semi‐hydrogenation process, with superior performance to that of thermocatalytic route, shows attractive to bring an evolution in industrial hydrogenation technology to an economical and safe way.

Barrier-discharge source of cold hydrogen atoms in supersonic beams: Stark effect in the 1s–2s transition

An intense source of cold hydrogen atoms in a supersonic beam is presented. H and D atoms are produced from pure samples of H2 and D2 using a barrier discharge near the orifice of a cryogenic pulsed valve. The atoms are entrained in the supersonic expansion of the precursor molecules and cool down to translational temperatures as low as mK. The H-atom density at a distance of 1.2 m from the valve orifice is estimated to be around 108 cm−3. The mean velocity of the supersonic beam containing the H (D) atoms can be adjusted between 2600 and 1200 m s−1 (between 1850 and 820 m s−1). The barrier discharge also produces and ions with n ranging from 2 to 8, which can be deflected off the beam by electric fields. The use of this H-atom source in spectroscopic measurements is demonstrated by an investigation of the Stark effect in the 1s–2s two-photon transition of H and D. A near-Fourier-transform-limited pulsed laser generating pulses of UV radiation of adjustable pulse length between 10 and 200 ns near 243 nm is used to record spectra with full resolution of the hyperfine structure in the s states, providing a textbook example of the Stark effect in the simplest set of near-degenerate states of one-electron atoms.

Research progress on selective C–C bond activation by group 9 metalloporphyrins

<p indent="0mm">The selective C–C bond activation of organic molecules with transition metal complexes has been studied in great demand in organic chemistry. Transition metal-carbon bonded intermediates, generated in C–C bond activation, could be further converted to new functionalized organic compounds. This review summarizes the research progress on selective C–C bond activation by group 9 metalloporphyrins in our group and other teams. It focuses on the activeM(por) intermediates, M^I(por)⁻ anion, M^II(por) radical and M^III(por)OH (M = Ir, Rh, Co; por = porphyrinato dianion), which achieved the selective stoichiometric C–C bond activation of ketones, esters, amides, nitriles, TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl), ethers and cycloalkanes, as well as the catalytic conversion for hydrogenolysis of C–C bond with H₂O, isopropanol, DMF as hydrogen atom source, and oxidation of C–C bond with H₂O as oxidant. The improvement and future development are also discussed.

Green Reductive Regioselective Opening of Epoxides: A Green Chemistry Laboratory Experiment

Green chemistry is finding its place as one of the most essential study topics in the curriculum of future chemists and chemical engineers. Experiments that meet green chemistry principles contribute to make the laboratory a safer working place, generate less waste, and allow students to increase their knowledge in new environmentally friendly chemical methodologies. The work reported here focuses on the reductive opening of epoxides to afford the less substituted alcohols, which can be carried out at room temperature under catalytic conditions and using water as a hydrogen atom source. The results of this work, as well as a procedure which allows the initiation of students in the application of green chemistry techniques through a particular example, are reported. This laboratory practice can be used to teach organic and radical chemistry, green chemistry principles, and product analysis (thin layer chromatography, flash chromatography, 1H NMR spectroscopy, and IR spectroscopy).

Nickel(II) phosphine-catalysed hydrodehalogenation of aryl halides under mild ambient conditions

A convenient and low-cost hydrodehalogenation process catalysed by air-stable nickel(II) complexes containing bidentate phosphine ligands has been developed under ambient conditions with sodium borohydride acting as the reducing agent and hydrogen atom source. High conversions of aryl halides, including polyfluorinated substrates, into their hydrogenated counterparts have been achieved in dimethylformamide (DMF) and to a moderate extent, in DMF/isopropanol (10:90% v/v) solvent mixture. A mechanism has been proposed to account for the experimental data.