Hydride Atom Research Articles

Taming CO2•- via Synergistic Triple Catalysis in Anti-Markovnikov Hydrocarboxylation of Alkenes.

The direct utilization of carbon dioxide as an ideal one-carbon source in value-added chemical synthesis has garnered significant attention from the standpoint of global sustainability. In this regard, the photo/electrochemical reduction of CO2 into useful fuels and chemical feedstocks could offer a great promise for the transition to a carbon-neutral economy. However, challenges in product selectivity continue to limit the practical application of these systems. A robust and general method for the conversion of CO2 to the polarity-reversed carbon dioxide radical anion, a C1 synthon, is critical for the successful valorization of CO2 to selective carboxylation reactions. We demonstrate herein a hydride and hydrogen atom transfer synergy driven general catalytic platform involving CO2•- for highly selective anti-Markovnikov hydrocarboxylation of alkenes via triple photoredox, hydride, and hydrogen atom transfer catalysis. Mechanistic studies suggest that the synergistic operation of the triple catalytic cycle ensures a low-steady-state concentration of CO2•- in the reaction medium. This method using a renewable light energy source is mild, robust, selective, and capable of accommodating a wide range of activated and unactivated alkenes. The highly selective nature of the transformation has been revealed through the synthesis of hydrocarboxylic acids from the substrates bearing a hydrogen atom available for intramolecular 1,n-HAT process as well as diastereoselective synthesis. This technology represents a general strategy for the merger of in situ formate generation with a synergistic photoredox and HAA catalytic cycle to provide CO2•- for selective chemical transformations.

Enhanced Efficiency of Amide‐Substituted Quinuclidine‐Boranes as Hydridic Hydrogen Atom Transfer Catalysts for Photoinduced Hydroalkylation of Unactivated Olefins†

Comprehensive SummaryAn amide‐substituted quinuclidine‐borane has been identified as a more efficient hydridic hydrogen atom transfer (HAT) catalyst for the hydroalkylation of unactivated olefins under visible‐light irradiation. 1H NMR titration experiments reveal that the amide moiety of the quinuclidine‐borane catalyst forms stronger hydrogen bonds with the carbonyl substrates, thereby improving the reaction yields. Furthermore, it was found that the reaction yields correlate well with the association constant between the quinuclidine‐borane catalyst and the carbonyl substrate. A scale‐up reaction using a continuous‐flow photoreactor has also been demonstrated.

A Systematic Study of the Solid-State Pathway from Melamine via Melaminate to Carbodiimide under Evolution of Hydrogen.

Thermal analysis techniques, such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), can provide valuable insights into thermal properties, intermediate phases, and phase transitions; sometimes even a whole series of compounds appears in a given system. The solid-state reaction pathway from melamine to carbodiimide, monitored by DSC, involves a sequence of chemical reactions and intermediate phases departing from the reaction of potassium hydride and melamine. The fully analyzed reaction cascade begins with the formation of potassium melaminate, K(C3N6H5), and progresses through several intermediate phases, each with distinct structures and properties, before ultimately yielding β-K2(CN2). All crystalline compounds appearing in this reaction sequence are identified using X-ray diffraction analyses. With a 6:1 ratio of potassium hydride and melamine, equal numbers of protic and hydridic hydrogen atoms in the starting materials favor the release of H2 until the formation of the final product K2(CN2), which appears with two modifications.

Biosynthetic Strategies of Berberine Bridge Enzyme-like Flavoprotein Oxidases toward Structural Diversification in Natural Product Biosynthesis.

Berberine bridge enzyme-like oxidases are often involved in natural product biosynthesis and are seen as essential enzymes for the generation of intricate pharmacophores. These oxidases have the ability to transfer a hydride atom to the FAD cofactor, which enables complex substrate modifications and rearrangements including (intramolecular) cyclizations, carbon-carbon bond formations, and nucleophilic additions. Despite the diverse range of activities, the mechanistic details of these reactions often remain incompletely understood. In this Review, we delve into the complexity that BBE-like oxidases from bacteria, fungal, and plant origins exhibit by providing an overview of the shared catalytic features and emphasizing the different reactivities. We propose four generalized modes of action by which BBE-like oxidases enable the synthesis of natural products, ranging from the classic alcohol oxidation reactions to less common amine and amide oxidation reactions. Exploring the mechanisms utilized by nature to produce its vast array of natural products is a subject of considerable interest and can lead to the discovery of unique biochemical activities.

Hydrogen Storage Capacity of Cobalt Cluster Ions.

The adsorption of H2 on gas-phase Con± (n = 5-12) clusters at 300 K and the desorption of H2 from ConHm± upon heating were studied experimentally by combining thermal desorption spectrometry and mass spectrometry to elucidate the hydrogen storage property of the Co clusters. Hydrogen atoms adsorbed well on Con+ (n = 5, 10-12) and Con- (n = 5-12) at 300 K to form ConHm±. The atomic ratios, m/n, for ConHm- (0.9-1.4) were higher than those for ConHm+ (0.2-1.1). According to density functional theory (DFT) calculations, the first few H2 molecules had a tendency to dissociatively adsorb onto the Co clusters. Further, the bonding nature of the H atoms was ionic, similar to the H atoms in the metallic hydrides. In contrast, H2, adsorbed molecularly, was explained in terms of σ complex formation. H2 molecules were desorbed from the clusters upon heating. The temperature dependences showed that ConHm- released H2 at a higher temperature (700-800 K) than ConHm+ (600-700 K), suggesting that Con- should have a higher affinity to hydrogen than Con+. The desorption temperatures were lower than those of VnHm+, which was consistent with the fact that the adsorption energies of H2 were lower for the Co clusters than those for the V clusters. The low adsorption energies were ascribed to their large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps in the Co clusters.

Structural alterations on copper cages containing hydrides coordinated to the central Pd(0)

A crucial component of nanocluster (NC) chemistry is the design and control of complex molecular architectures with atomic precision. Herein, we report the synthesis and structure of [PdH2Cu11{S2P(OiPr)2}6(CCPh)3] (PdH2Cu11), confirmed by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy, elemental analysis, and electrospray ionization mass spectrometry (ESI-MS). PdH2Cu11 is obtained from the reaction of a parent cluster [PdH2Cu14{S2P(OiPr)2}6(CCPh)6] (PdH2Cu14) with trifluoroacetic acid (TFA). Importantly the addition of TFA does not result in the loss of the hydride atoms located at the kernel, and H-Pd-H motif is retained. The molecular structure of PdH2Cu11 consists of a distorted 3,3,4,4,4-pentacapped trigonal prism Cu11 cage encapsulating a quasi-linear H-Pd-H unit, stabilized by dithiophosphate and alkynyl ligands. DFT calculations suggest an ionic inclusion complex of the type [{PdH2}2−]@[{Cu11{S2P(OiPr)2}6(CCPh)3}2+] and confirm the hydride positions. A non-covalent inter-cluster interaction results in the unique formation of a unique honeycomb crystal lattice. Overall, this work broadens and deepens the understanding of Pd-Cu hydride alloy nanoclusters.

First‐Row Transition Metal‐Catalyzed Single Hydroelementation of N‐Heteroarenes

AbstractCatalytic partial reduction of N‐heteroarenes with H2 or H[E] (E=Si, B‐based) has been a useful and general method for synthesis of a broad range of dihydropyridines (DHP) and dihydroquinolines (DHQ). In recent seven years, one of the most notable advances in this context is being able to utilize earth‐abundant and inexpensive first‐row transition metal‐based catalytic systems. These catalytic procedures are generally considered more environmentally benign and sustainable when compared to conventional catalytic systems relying on precious metals. This Review describes 20 molecular catalytic systems based on first‐row transition metals for selective single hydroelementation of pyridines and quinolines with H2 surrogate, hydrosilanes, and hydroboranes providing 1,2‐ or 1,4‐dihydropyridines and ‐dihydroquinolines. The observed reaction profiles such as scope and activity are briefly presented, while the proposed working modes over a series of elemental steps – H−[E] bond cleavage, hydride (H−) or hydrogen atom (H⋅) transfer, and product release, are discussed in detail on the basis of experimental and/or computational mechanistic observations and insights.

Diffusion flame, heated quartz tube or dielectric barrier discharge? Comparing the resistance of hydride atomizers towards interferences with detection by atomic absorption spectrometry

The resistance of three types of hydride atomizers towards interferences from other hydride forming elements and mercury was comprehensively investigated. Four hydride forming elements (Pb, Bi, Se and Te) were used as model analytes while seven hydride forming elements and mercury were investigated as potential interferents. The atomizers studied were based on a diffusion flame - DF, an externally heated quartz tube (multi)atomizer - (MM)QTA as well as a dielectric barrier discharge plasma - DBD. The performance of even two designs of DBD atomizers was compared. The first configuration (REF-SIN) was realized by a DBD chamber with glued electrodes coupled to a power supply source with sinusoidal modulation of high voltage. The second configuration of the DBD atomizer (SE-SW) comprised of a DBD chamber with the sputtered electrodes powered by a square-wave modulated high voltage source. The DF atomizer was found to be the most robust towards atomization interferences. However, its sensitivity was 30 to 50 times lower compared to (MM)QTA and DBD based atomizers due to its short optical path. The DBD atomizer in REF-SIN arrangement can compete very well with (MM)QTA atomizer in terms of resistence to interferences as well as sensitivity. The resistence of DBD atomizer in SE-SW configuration towards atomization interferences is slightly worse compared to (MM)QTA and DBD in REF-SIN design.

Ba12 [BN2 ]6.67 H4 : A Disordered Anti-Skutterudite filled with Nitridoborate Anions.

Skutterudites are of high interest in current research due to their diversity of structures comprising empty, partially filled and filled variants, mostly based on metallic compounds. We herein present Ba12 [BN2 ]6.67 H4 , forming a non-metallic filled anti-skutterudite. It is accessed in a solid-state ampoule reaction from barium subnitride, boron nitride and barium hydride at 750 °C. Single-crystal X-ray and neutron powder diffraction data allowed to elucidate the structure in the cubic space group Im (no. 204). The barium and hydride atoms form a three-dimensional network consisting of corner-sharing HBa6 octahedra and Ba12 icosahedra. Slightly bent [BN2 ]3- units are located in the icosahedra and the voids in-between. 1 H and 11 B magic angle spinning (MAS) NMR experiments and vibrational spectroscopy further support the structure model. Quantum chemical calculations coincide well with experimental results and provide information about the electronic structure of Ba12 [BN2 ]6.67 H4 .

Ba12[BN2]6.67H4: A Disordered Anti‐Skutterudite filled with Nitridoborate Anions

AbstractSkutterudites are of high interest in current research due to their diversity of structures comprising empty, partially filled and filled variants, mostly based on metallic compounds. We herein present Ba12[BN2]6.67H4, forming a non‐metallic filled anti‐skutterudite. It is accessed in a solid‐state ampoule reaction from barium subnitride, boron nitride and barium hydride at 750 °C. Single‐crystal X‐ray and neutron powder diffraction data allowed to elucidate the structure in the cubic space group Im (no. 204). The barium and hydride atoms form a three‐dimensional network consisting of corner‐sharing HBa6 octahedra and Ba12 icosahedra. Slightly bent [BN2]3− units are located in the icosahedra and the voids in‐between. 1H and 11B magic angle spinning (MAS) NMR experiments and vibrational spectroscopy further support the structure model. Quantum chemical calculations coincide well with experimental results and provide information about the electronic structure of Ba12[BN2]6.67H4.

The Theoretical Investigation by QTAIM Approach to Chemical Bonding of a Di-Rhenium Bis(Triphenylphosphine) Carbonyl Cluster Containing Sulfuric and Hydrido Bridge: [Re2(CO)6(μ-S)(μ-H)(PPh3)2

Scientists used the quantum theory of atoms in molecules (QTAIM) to calculate and interpret various electron density parameters for a di-rhenium bis(triphenylphosphine) carbonyl cluster containing sulfuric and hydrido bridge: [Re2(CO)6(μ-S)(μ-H)(PPh3)2]. They analyzed the bond critical points and compared them with data from previous organometallic system studies. The researchers were able to compare the topological processes of different atom-atom interactions based on these results.
 The calculations showed that there were no bond critical points or identical bond paths between Re-Re in the core of the cluster. The electron density distribution was affected by the position of bridging hydride and sulfur atoms coordinated to Re-Re, which significantly affected the bonds between these transition metal atoms. However, the calculations did confirm the presence of a 6c–8e bonding interaction delocalized over HRe2SP2 in the cluster.
 The scientists found that the Re-H and Re-S bonds in this cluster exhibited typical closed-shell interactions, with small values for ρ(b) and Laplacian ∇2ρ(b) above zero and small positive values for total energy density H(b). Similarly, the bond interactions between phosphine metal atoms and the C atoms of the phenyl ring ligands showed properties similar to open-shell interactions in the QTAIM classification.

Challenges and capabilities of quantum crystallography for locating hydrogen atoms in transition metal hydrides

Challenges and capabilities of quantum crystallography for locating hydrogen atoms in transition metal hydrides

Study the Chemical Bonding of Heterometallic Trinuclear Cluster Containing Cobalt and Ruthenium: [(Cp*Co) (CpRu)2 (μ3-H) (μ-H)3] using QTAIM Approach

The topological parameters of the metal-metal and metal-ligand bonding interactions in a trinuclear tetrahydrido cluster [(Cp*Co) (CpRu)2 (μ3-H) (μ-H)3]1 (Cp* = η5 -C5Me4Et), (Cp = η5 -C5Me5), was explored by using the Quantum Theory of Atoms-in-Molecules (QTAIM). The properties of bond critical points such as the bond delocalization indices δ (A, B), the electron density ρ(r), the local kinetic energy density G(r), the Laplacian of the electron density ∇2ρ(r), the local energy density H(r), the local potential energy density V(r) and ellipticity ε(r) are compared with data from earlier organometallic system studies. A comparison of the topological processes of different atom-atom interactions has become possible thanks to these results. In the core of the heterometallic tetrahydrido cluster, the Ru2CoH4 part, the calculations show no existence of any bond critical points (BCP) or identical bond paths (BPs) between Ru-Ru and Ru-Co. Electron densities are determined by the position of bridging hydride atoms coordinated to Ru-Ru and Ru-Co, which significantly affects the bonds between these transition metal atoms. On the other hand, the results confirm that the cluster under study contains a 7c–11e bonding interaction delocalized over M3H4, as shown by the non-negligible delocalization index calculations. The small values for electron density ρ(b) above zero, together with the small values, again above zero, for Laplacian ∇2ρ(b) and the small positive values for total energy density H(b), are shown by the Ru-H and Co-H bonds in this cluster is typical for open-shell interactions. Also, the topological data for the bond interactions between Co and Ru metal atoms with the C atoms of the cyclopentadienyl Cp ring ligands are similar. They show properties very identical to open-shell interactions in the QTAIM classification.

A Theoretical Investigation of Chemical Bonding of a Heterometallic Trinuclear Cluster Containing Iridium and Ruthenium: [(Cp*Ir) (CpRu)2 (μ3-H) (μ-H)3] by QTAIM Approach

Numerous integral and local electron density’s topological parameters of significant metal-metal and metal-ligand bonding interactions in a trinuclear tetrahydrido cluster [(Cp* Ir) (Cp Ru)2 (μ3-H) (μ-H)3]1 (Cp = η5 -C5Me5), (Cp* = η5 -C5Me4Et) were calculated and interpreted by using the quantum theory of atoms in molecules (QTAIM). The properties of bond critical points such as the delocalization indices δ (A, B), the electron density ρ(r), the local kinetic energy density G(r), the Laplacian of the electron density ∇2ρ(r), the local energy density H(r), the local potential energy density V(r) and ellipticity ε(r) are compared with data from earlier organometallic system studies. A comparison of the topological processes of different atom-atom interactions has become possible thanks to these results. In the core of the heterometallic tetrahydrido cluster, the Ru2IrH4 part, the calculations showed that there are no bond critical points (BCPs) or identical bond paths (BPs) between Ru-Ru and Ru-Ir. The distribution of electron densities is determined by the position of bridging hydride atoms coordinated to Ru-Ru and Ru-Ir, which significantly affects the bonds between these transition metal atoms. On the other hand, the results confirm that the cluster under study contains a 7c–11e bonding interaction delocalized over M3H4, as shown by the non-negligible delocalization index calculations. The small values for ρ(b) above zero, together with the small values, again above zero, for Laplacian ∇2ρ(b) and the small positive values for total energy density H(b), are shown by the Ru-H and Ir-H bonds in this cluster is typical for open-shell interactions. Also, the topological data for the bond interactions between Ir and Ru metal atoms with the C atoms of the cyclopentadienyl Cp ring ligands are similar. They show properties very identical to open-shell interactions in the QTAIM classification.

Four-Step Synthesis of (-)-4-epi-Presilphiperfolan-8α-ol by Intramolecular Iron Hydride Atom Transfer-Mediated Ketone-Alkene Coupling and Studies to Access trans-Hydrindanols with a Botryane Scaffold.

From an (R)-(+)-pulegone-derived building block that incorporates the stereo-defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four-step synthesis of (-)-4-epi-presilphiperfolan-8-α-ol was achieved. The key processes involved are a ring-closing metathesis leading to a bridged alkene-tethered ketone and its subsequent FeIII -mediated metal-hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon-centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans-fused hydrindanols structurally related to botrydial compounds.

Next generation of dielectric barrier discharge hydride atomizers for atomic absorption spectrometry: A case study on Pb, Bi, Se and Te

The performance of hydride atomizers based on dielectric barrier discharge (DBD) was evaluated by atomic absorption spectrometry as a detector employing Pb, Bi, Se and Te as model analytes. Two designs of DBD atomizers either with glued or sputtered electrodes were investigated in combination with sinusoidal or square-wave modulated high voltage power supply sources. Moreover, the effect of gas phase dryers on analyte response was studied. Nafion tubes were found as universal dryers capable of efficient water vapor removal with no losses of analyte. Sensitivity was compared among individual DBD configurations being related also to conventional externally heated quartz tube (multi)atomizers (MM)QTA. For Te and Se comparable sensitivities were reached in all configurations of DBD atomizers and MMQTA. On the contrary, QTA provided three times higher sensitivity for Bi and Pb than DBD atomizers. Sensitivity reached among DBD atomizers was the same regardless of their electrode design and high voltage waveform modulation for Se, Te and Bi. Differences in sensitivity were observed for Pb depending on DBD atomizer configuration. Here the best sensitivity was found in DBD with sputtered electrodes coupled to power source with square-wave modulation of high voltage. It was twice higher than that reached in the DBD atomizer with glued electrodes powered by sine-wave voltage. The sensitivity in DBD atomizers correlates negatively with the amount of analyte deposited in the atomizer during atomization. >90% of Bi and Pb introduced into the system is deposited while the deposited fraction of Te and Se, respectively, decreases to 60% and 35%.

Selected Ion Flow Tube Mass Spectrometry as a Tool to Understand Hydride Atomization and the Fate of Free Analyte Atoms in an Externally Heated Quartz Tube Atomizer.

Hydride atomization and the fate of free analyte atoms in an externally heated quartz tube atomizer (QTA) were investigated employing selected ion flow tube mass spectrometry (SIFT-MS). SIFT-MS proved to be ideally suited to study water concentration in gases leaving the atomizer. This made it possible to quantify the oxygen "contaminant" flow rate to QTA as 0.04-0.05 mL min-1. This is valid for typical conditions of hydride generation. Most significantly, studies of temperature influence on water concentration resulted in detailed insight into hydrogen radical-forming reactions between oxygen and hydrogen. Minimum QTA temperatures required to generate hydrogen radicals under a variety of different flow rates and compositions of the QTA atmosphere were found to be in the range between 585 and 800 °C. The ability of SIFT-MS to detect extremely low concentrations of arsane and selane was employed to quantify the fraction of As and Se removed from the QTA in the form of hydride in dependence on QTA temperature under typical conditions of hydride generation. It was found that free As atoms formed by atomization of arsane decay to different species than to arsane. In the case of selane under typical atomization conditions, the efficiency of the decay of free Se atoms to selane was between 50 and 100% in dependence on actual flow rates and compositions of the QTA atmosphere.

Lattice dynamics of high-pressure hydrides studied by inelastic neutron scattering

Due to the small mass and anomalously large neutron scattering cross-section of proton (about 80 barns compared to a few barns for other nuclei), inelastic neutron scattering is considered as one of the most effective tools in studying optical vibrations of hydrogen atoms in metal hydrides. The current review is focused on the binary hydrides of 3d- and 4d-metals of groups VI–VIII, which were produced at high hydrogen pressures of several gigapascals in relatively large quantities of hundreds of mg, quenched to low temperature and studied by INS ex situ at ambient pressure with high statistical accuracy. One of the unusual effects revealed by INS is a strong increase in the strength of the metal-hydrogen interactions with decreasing atomic number of the d-metal accompanied by an increase in the Me-H distance. Based on the available experimental results, the spectra g(E) of the phonon density of states and temperature dependencies CV(T) of the heat capacity at constant volume at T up to 1000 K have been derived in this paper and presented both in the figures and in digital form. This provides the reference data for the theoretical investigations of the crystal structures and compositions of new practically important hydrides giving the opportunity to validate calculation methods by comparing the calculated g(E) and CV(T) with the accurate experimental dependencies for the binary hydrides. Recent INS studies showed [R.A. Klein et al., J. Alloy. Compd. 894 (2022) 162381] that the fingerprints of anomalously short H-H separations of 1.6 Å violating the “2 Å rule” can be easily and unambiguously identified in the complex INS spectra of quaternary hydrides (La,Ce)NiInH1+x. This makes neutron spectroscopy an attractive means for obtaining valuable data in the search for novel hydrides with a record high hydrogen capacity.

Atomization of As and Se volatile species in a dielectric barrier discharge atomizer after hydride generation: Fate of analyte studied by selected ion flow tube mass spectrometry

Atomization of hydrides and their methylated analogues in a dielectric barrier discharge (DBD) plasma atomizer was investigated. Selected ion flow tube mass spectrometry (SIFT-MS) was chosen as a detector being capable of selective detection of non-atomized original volatile species allowing thus direct quantification of atomization efficiency. Selenium hydride (SeH2) and three volatile arsenic species, namely arsenic hydride (AsH3), monomethylarsane (CH3AsH2) and dimethylarsane ((CH3)2AsH), were selected as model analytes. The mechanistic study performed contributes to understanding of the atomization processes in atomic absorption spectrometry (AAS). The presented results are compatible with a complete atomization of arsenic hydride as well as its methylated analogues and with atomization efficiency of SeH2 below 80%. Using AsH3 as a model analyte and a combination of AAS and SIFT-MS detectors has revealed that the hydride is not atomized, but decomposed in the DBD atomizer in absence of hydrogen fraction in the carrier gas. Apart from investigation of analyte atomization, the SIFT-MS detector is capable of quantitative determination of water vapor content being either transported to, or produced in the atomizer. This information is crucial especially in the case of the low-power/temperature DBD atomizer since its performance is sensitive to the amount of water vapor introduced into the plasma.

Electronic Structure and Superconductivity of Compressed Metal Tetrahydrides.

Tetrahydrides crystallizing in the ThCr2 Si2 structure type have been predicted to become stable for a plethora of metals under pressure, and some have recently been synthesized. Through detailed first-principles investigations we show that the metal atoms within these symmetry MH4 compounds may be divalent, trivalent or tetravalent. The valence of the metal atom and its radius govern the bonding and electronic structure of these phases, and their evolution under pressure. The factors important for enhancing superconductivity include a large number of hydrogenic states at the Fermi level, and the presence of quasi-molecular H units whose bonds have been stretched and weakened (but not broken) via electron transfer from the electropositive metal, and via a Kubas-like interaction with the metal. Analysis of the microscopic mechanism of superconductivity in MgH4 , ScH4 and ZrH4 reveals that phonon modes involving a coupled libration and stretch of the H units leading to the formation of more complex hydrogenic motifs are important contributors towards the electron phonon coupling mechanism. In the divalent hydride MgH4 , modes associated with motions of the hydridic hydrogen atoms are also key contributors, and soften substantially at lower pressures.