Mass Spectrometry for Synthesis and Analysis

Mild Catalyst- and Additive-Free Three-Component Synthesis of 3-Thioisoindolinones and Tricyclic γ-Lactams Accelerated by Microdroplet Chemistry

Isoindolinones, bearing both γ-lactam and aromatic rings, draw extensive interest in organic, pharmaceutical, and medicinal communities as they are important structural motifs in many natural products, bioactive compounds, and pharmaceuticals. As the main contributor to isoindolinone synthesis, metal catalysis is associated with many drawbacks including essential use of toxic/precious metals and excessive additives, high reaction temperatures, specially predesigned starting materials, and long reaction times (typically 8-30 h). In this study, we developed a catalyst- and additive-free, minute-scale, and high-yield microdroplet method for tricomponent isoindolinone synthesis at mild temperatures. By taking advantage of the astonishing reaction acceleration (1.9 × 102-9.4 × 103 acceleration factor range with a typical rate acceleration factor of 1.51 × 103 for the prototype reaction as the ratio of rate constants by microdroplet and bulk phase), 12 3-thioisoindolinones and two tricyclic γ-lactams were synthesized using various 2-acylbenzaldehydes, amines, and thiols with satisfactory yields ranging from 85% to 97% as well as a scale-up rate of 3.49 g h-1. Because of the advantages (no use of any catalysts or additives, mild temperature, rapid and satisfactory conversion, broad substrate scope, and gram scalability), the microdroplet method represents an attractive alternative to metal catalysis for laboratory synthesis of isoindolinones and their derivatives.

Molecular Dynamics Simulations of Soft and Reactive Landing of Proteins Desorbed by Argon Cluster Bombardment

Reactive molecular dynamics (MD) simulations were conducted to investigate the soft and reactive landing of hyperthermal velocity proteins transferred to a vacuum using large argon clusters. Experimentally, the interaction of argon cluster ion beams (Ar1000-5000+) with a target biofilm was previously used in such a manner to transfer lysozymes onto a collector with the retention of their bioactivity, paving the way to a new solvent-free method for complex biosurface nanofabrication. However, the experiments did not give access to a microscopic view of the interactions needed for their full understanding, which can be provided by the MD model. Our reactive force field simulations clarify the landing mechanisms of the lysozymes and their fragments on collectors with different natures (gold- and hydrogen-terminated graphite). The results highlight the conditions of soft and reactive landing on rigid surfaces, the effects of the protein structure, energy, and incidence angle before landing, and the adhesion forces with the collector substrate. Many of the obtained results can be generalized to other soft and reactive landing approaches used for biomolecules such as electrospray ionization and matrix-assisted laser desorption ionization.

Is Reaction Acceleration of Microdroplet Chemistry Favorable to Controlling the Enantioselectivity?

Microdroplet chemistry has been proven to amazingly accelerate many chemical and biological reactions in the past 2 decades. Current microdroplet accelerated reactions are predominantly symmetric synthetic but minorly asymmetric synthetic reactions, where stereoselectivity is scarcely concerned. This study selected unimolecular and bimolecular reactions, multicomponent Passerini reactions, and enzymatic ketone reduction as the model reactions to illustrate whether reaction acceleration of microdroplet chemistry is favorable to retaining a chiral center and controlling the enantioselectivity or not. The results illustrated that microdroplet chemistry did not disrupt pre-existing stereogenic centers in chiral starting materials during reactions but did harm to stereospecificity in asymmetric catalysis by chiral catalysts and chiral organic ligands with the exclusion of enzymatic reactions. Our preliminary study reminds us of more cautions to the product enantioselectivity when conducting asymmetric catalysis in microdroplets. We also hope this study may promote more valuable further research on the stereoselectivity of microdroplet chemistry.

Catalyst-Free Accelerated Three-Component Synthesis of Betti Bases in Microdroplets

Due to their important roles in medicine and asymmetric metal catalysis, the formation of Betti bases has attracted wide interest in organic chemical community. Traditional multicomponent reaction methods for synthesizing Betti bases normally require long reaction times under harsh conditions (high temperature, microwave or ultrasonic irradiation, etc.) in the presence of various catalysts. In this study, we developed a mild, highly efficient and environmentally friendly method to synthesize Betti bases without the use of any catalysts in microdroplets. The Betti reaction was accelerated by 6.53×10³ in microdroplets by comparing the measured rate constant in bulk. Fifteen Betti bases were synthesized by the microdroplet method using a variety of aldehydes, naphthols and amines with 68-98 % yields at a scaled-up amount of 1.9 g h^-1 . Overall it is an attractive alternative to classic organic synthesis for the construction of Betti bases and derivatives.

Suzuki C-C Coupling in Paper Spray Ionization: Microsynthesis of Biaryls and High-Sensitivity MS Detection of Aryl Bromides

Suzuki-Miyaura cross-coupling is one of the most powerful strategies for constructing biaryl compounds. However, classic Suzuki-Miyaura coupling suffers from hour-scale reaction time and competitive protodeboronation. To address these problems, a mild nonaqueous potassium trimethylsilanolate (TMSOK)-assisted Suzuki-Miyaura coupling strategy was designed for the microsynthesis of biaryls in paper spray ionization (PSI). Due to the acceleration power facilitated by microdroplet chemistry in reactive PSI, the microsynthesis of biaryls by reactive PSI was accomplished within minutes with comparable yields to the bulk, showing good substrate applicability from 32 Suzuki-Miyaura reactions of aryl bromides and aryl boronic acid/borates bearing different substituents. Based on the above TMSOK-assisted Suzuki-Miyaura coupling strategy, we further developed a high-sensitivity and selective PSI mass spectrometry (MS) method for quantitative analysis of aryl bromides, a class of environmentally persistent organic pollutants that cannot be directly detected by ambient mass spectrometry due to their low ionization efficiency. In situ derivatization of aryl bromides was achieved with aryl borates bearing quaternary ammonium groups in PSI. The proposed PSI-MS method shows good linearity over the 0.01-10 μmol L^-1 range with low detection limits of 1.8-4.8 nmol L^-1 as well as good applicability to the rapid determination of six aryl bromides in three environmental water samples. The proposed PSI-MS method also shows good applicability to brominated flame retardants (polybrominated diphenyls/diphenyl esters). Overall, this study provides a simple, rapid, low-cost, high-sensitivity, and high-selectivity strategy for trace aryl bromides and other brominated pollutants in real samples with minimal/no sample pretreatment.

Spontaneous Oxidation of Aromatic Sulfones to Sulfonic Acids in Microdroplets

Reactions in microdroplets can be accelerated and can present unique chemistry compared to reactions in bulk solution. Here, we report the accelerated oxidation of aromatic sulfones to sulfonic acids in microdroplets under ambient conditions without the addition of acid, base, or catalyst. The experimental data suggest that the water radical cation, (H₂O)^+•, derived from traces of water in the solvent, is the oxidant. The substrate scope of the reaction indicates the need for a strong electron-donating group (e.g., p-hydroxyl) in the aromatic ring. An analogous oxidation is observed in an aromatic ketone with benzoic acid production. The shared mechanism is suggested to involve field-assisted ionization of water at the droplet/air interface, its reaction with the sulfone (M) to form the radical cation adduct, (M + H₂O)^+•, followed by 1,2-aryl migration and C-O cleavage. A remarkably high reaction rate acceleration (∼10³) and regioselectivity (∼100-fold) characterize the reaction.

Spontaneous Water Radical Cation Oxidation at Double Bonds in Microdroplets

Spontaneous oxidation of compounds containing diverse X=Y moieties (e.g., sulfonamides, ketones, esters, sulfones) occurs readily in organic-solvent microdroplets. This surprising phenomenon is proposed to be driven by the generation of an intermediate species [M+H₂O]^+·: a covalent adduct of water radical cation (H₂O^+·) with the reactant molecule (M). The adduct is observed in the positive ion mass spectrum while its formation in the interfacial region of the microdroplet (i.e., at the air-droplet interface) is indicated by the strong dependence of the oxidation product formation on the spray distance (which reflects the droplet size and consequently the surface-to-volume ratio) and the solvent composition. Importantly, based on the screening of a ca. 21,000-compound library and the detailed consideration of six functional groups, the formation of a molecular adduct with the water radical cation is a significant route to ionization in positive ion mode electrospray, where it is favored in those compounds with X=Y moieties which lack basic groups. A set of model monofunctional systems was studied and in one case, benzyl benzoate, evidence was found for oxidation driven by hydroxyl radical adduct formation followed by protonation in addition to the dominant water radical cation addition process. Significant implications of molecular ionization by water radical cations for oxidation processes in atmospheric aerosols, analytical mass spectrometry and small-scale synthesis are noted.

Applications and Techniques for Fast Machine Learning in Science

In this community review report, we discuss applications and techniques for fast machine learning (ML) in science-the concept of integrating powerful ML methods into the real-time experimental data processing loop to accelerate scientific discovery. The material for the report builds on two workshops held by the Fast ML for Science community and covers three main areas: applications for fast ML across a number of scientific domains; techniques for training and implementing performant and resource-efficient ML algorithms; and computing architectures, platforms, and technologies for deploying these algorithms. We also present overlapping challenges across the multiple scientific domains where common solutions can be found. This community report is intended to give plenty of examples and inspiration for scientific discovery through integrated and accelerated ML solutions. This is followed by a high-level overview and organization of technical advances, including an abundance of pointers to source material, which can enable these breakthroughs.

Direct Phosphonylation of N-Phenyltetrahydroisoquinolines in Microdroplets

Because of their unique properties and high biological activities, organophosphorus compounds have been used worldwide in agricultural, industrial, medicinal, and veterinary applications. Conventional strategies for direct phosphonylation suffer from the usage of stoichiometric or excessive metallic or nonmetallic catalysts and long reaction times under harsh conditions, leading to a strong desire for environment-friendly protocols for phosphonylation. A protocol for the accelerated phosphonylation of N-phenyltetrahydroisoquinolines in minutes was developed without the use of any catalyst in microdroplets. The phosphonylation process was completed (>85% yields) in 10 min at 40 °C using 0.8 equiv 2,3-dicyano-5,6-dichlorobenzoquinone as the oxidant and acetonitrile as the solvent. The microdroplet phosphonylation strategy showed good suitability to alkyl phosphites and N-phenyltetrahydroisoquinolines bearing electron-withdrawing and electron-donating substitutes, and the yields of the microdroplet reaction were much greater than those of the bulk (accelerated by two orders of magnitude from the ratio of the rate constants using the microdroplet and the bulk method). Furthermore, microdroplet phosphonylation can be scaled up to a 1-phenyl-2-dimethylphosphonite-1,2,3,4-tetrahydroisoquinoline amount of 510 mg h^-1 by spraying 0.1 mol L^-1 N-phenyltetrahydroisoquinoline at 300 μL min^-1. These figures of merit make it a promising alternative to classic organic methodologies for the synthesis of organophosphorus compounds.

Accelerated synthesis of energetic precursor cage compounds using confined volume systems

Confined volume systems, such as microdroplets, Leidenfrost droplets, or thin films, can accelerate chemical reactions. Acceleration occurs due to the evaporation of solvent, the increase in reactant concentration, and the higher surface-to-volume ratios amongst other phenomena. Performing reactions in confined volume systems derived from mass spectrometry ionization sources or Leidenfrost droplets allows for reaction conditions to be changed quickly for rapid screening in a time efficient and cost-saving manner. Compared to solution phase reactions, confined volume systems also reduce waste by screening reaction conditions in smaller volumes prior to scaling. Herein, the condensation of glyoxal with benzylamine (BA) to form hexabenzylhexaazaisowurtzitane (HBIW), an intermediate to the highly desired energetic compound 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), was explored. Five confined volume systems were compared to evaluate which technique was ideal for forming this complex cage structure. Substituted amines were also explored as BA replacements to screen alternative cage structure intermediates and evaluate how these accelerated techniques could apply to novel reactions, discover alternative reagents to form the cage compound, and improve synthetic routes for the preparation of CL-20. Ultimately, reaction acceleration is ideal for predicting the success of novel reactions prior to scaling up and determining if the expected products form, all while saving time and reducing costs. Acceleration factors and conversion ratios for each reaction were assessed by comparing the amount of product formed to the traditional bulk solution phase synthesis.

Reaction Acceleration Promoted by Partial Solvation at the Gas/Solution Interface

The kinetics of organic reactions of different types in microvolumes (droplets, thin films, and sealed tubes) show effects of gas/solution interfacial area, reaction molecularity and solvent polarity. Partial solvation at the gas/solution interface is a major contributor to the 10⁴ -fold reaction acceleration seen in bimolecular but not unimolecular reactions in microdroplets. Reaction acceleration can be used to manipulate selectivity by solvent choice.

MODERN PLASMA-BASED DESORPTION/IONIZATION: FROM ATOMS AND MOLECULES TO CHEMICAL SYNTHESIS

Since the first mass spectrometry (MS) experiments were conducted by Thomson and Aston, plasmas have been used as ionization sources. Historically, plasma ion sources were used for these experiments because they were one of the few known sources of gas-phase ions at the time and they were relatively simple to setup and operate. Since then, developments in plasma ionization have continued to inform and motivate advances in other areas of MS. For example, plasma-desorption MS demonstrated ionization of large peptides and polymers more than 10 years before the first descriptions of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). As a result, significant effort was placed on development of ionization approaches, mass analysis, and detection approaches for very large molecules: even before the advent of ESI and MALDI. Since then, new analytical challenges and opportunities in plasma ionization have arisen. In this review, the emerging trends in plasma-based ionization for several areas of MS will be discussed, including molecular ionization, elemental ionization, hybrid elemental and molecular ion sources, and unique chemical transformations. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Recent Advances of In-Source Electrochemical Mass Spectrometry

Hyphenation of electrochemistry (EC) and mass spectrometry has become a powerful tool to study redox processes. Approaches that can achieve this hyphenation include integrating chromatography/electrophoresis between electroinduced redox reactions and detection of products, coupling an EC flow cell to a mass spectrometer, and performing electrochemical reactions inside the ion source of a mass spectrometer. The first two approaches have been well reviewed elsewhere. This Minireview highlights the inherent electrochemical properties of many mass spectrometry ion sources and their roles in the coupling of electrochemistry and mass spectrometric analysis. Development of modified ion sources that allow the compatibility of electrochemistry with ionization processes is also surveyed. Applications of different in-source electrochemical devices are provided including intermediate capturing, bioanalytical studies, nanoparticle formation, electrosynthesis, and electrode imaging.

Reaction Kinetics of Organic Aerosol Studied by Droplet Assisted Ionization: Enhanced Reactivity in Droplets Relative to Bulk Solution

Droplet Assisted Ionization (DAI) is a relatively new method for online analysis of aerosol droplets that enables measurement of the rate of an aerosol reaction. Here, we used DAI to study the reaction of carbonyl functionalities in secondary organic aerosol (SOA) with Girard's T (GT) reagent, a reaction that can potentially be used to enhance the detection of SOA in online measurements. SOA was produced by α-pinene ozonolysis. Particulate matter was collected on a filter, extracted, and mixed with GT reagent in water. While the reaction hardly proceeded at all in bulk solution, products were readily observed with DAI when the solution was atomized to produce micron-size droplets. Varying the droplet transit time between the atomizer and mass spectrometer allowed the reaction rate constant to be determined, which was found to be 4 orders of magnitude faster than what would be expected from bulk solution kinetics. Decreasing the water content of the droplets, either by heating the capillary inlet to the mass spectrometer or by decreasing the relative humidity of the air surrounding the droplets in the transit line from the atomizer to the mass spectrometer, enhanced product formation. The results suggest that reaction enhancement occurs at the droplet surface, which is consistent with previous reports of reaction acceleration during mass spectrometric analysis, where a bulk solution is analyzed with an ionization method that produces aerosol droplets.

Accelerated reactions of amines with carbon dioxide driven by superacid at the microdroplet interface

Microdroplets display distinctive interfacial chemistry, manifested as accelerated reactions relative to those observed for the same reagents in bulk. Carbon dioxide undergoes C–N bond formation reactions with amines at the interface of droplets to form carbamic acids. Electrospray ionization mass spectrometry displays the reaction products in the form of the protonated and deprotonated carbamic acid. Electrosonic spray ionization (ESSI) utilizing carbon dioxide as nebulization gas, confines reaction to the gas–liquid interface where it proceeds much faster than in the bulk. Intriguingly, trace amounts of water accelerate the reaction, presumably by formation of superacid or superbase at the water interface. The suggested mechanism of protonation of CO₂ followed by nucleophilic attack by the amine is analogous to that previously advanced for imidazole formation from carboxylic acids and diamines.

Microdroplets display distinctive interfacial chemistry, manifested as accelerated reactions relative to those observed for the same reagents in bulk.

Accelerated Reaction Kinetics in Microdroplets: Overview and Recent Developments

Various organic reactions, including important synthetic reactions involving C-C, C-N, and C-O bond formation as well as reactions of biomolecules, are accelerated when the reagents are present in sprayed or levitated microdroplets or in thin films. The reaction rates increase by orders of magnitude with decreasing droplet size or film thickness. The effect is associated with reactions at the solution-air interface. A key factor is partial solvation of the reagents at the interface, which reduces the critical energy for reaction. This phenomenon is of intrinsic interest and potentially of practical value as a simple, rapid method of performing small-scale synthesis.

A Gas-Phase Reaction Accelerator Using Vortex Flows

Gas-phase microdroplets have been increasingly used for reaction acceleration. Here, we report the development of a vortex tube as a reaction accelerator. Three types of reactions, viz., aromatization, amination isomerization, and acid-induced cytochrome c unfolding were used to characterize the performance of the vortex tube. During ion transfer from a nanoelectrospray ionization (nanoESI) source to the mass spectrometry (MS) inlet, the generated vortex flows helped droplet desolvation and ion confinement and thus improved the MS intensity by 2-3 orders of magnitude compared with that when the vortex tube was not applied. Like the stirring effect in the bulk phase, the reactants were more sufficiently mixed and reacted in vortices. Therefore, with the same reaction distance, a 2-3-fold improvement of conversion ratios was observed by using the vortices. Notably, the vortex tube enabled the use of flow rate to control the reaction time for ∼60 μs, which was useful for precise control of reaction progress. As a demonstration, the intermediates of the amination isomerization were tracked and the equilibrium constant and rate constant of the cytochrome c unfolding were determined.

Accelerating Electrochemical Reactions in a Voltage-Controlled Interfacial Microreactor

Microdroplet chemistry is attracting increasing attention for accelerated reactions at the solution-air interface. We report herein a voltage-controlled interfacial microreactor that enables acceleration of electrochemical reactions which are not observed in bulk or conventional electrochemical cells. The microreactor is formed at the interface of the Taylor cone in an electrospray emitter with a large orifice, thus allowing continuous contact of the electrode and the reactants at/near the interface. As a proof-of-concept, electrooxidative C-H/N-H coupling and electrooxidation of benzyl alcohol were shown to be accelerated by more than an order of magnitude as compared to the corresponding bulk reactions. The new electrochemical microreactor has unique features that allow i) voltage-controlled acceleration of electrochemical reactions by voltage-dependent formation of the interfacial microreactor; ii) "reversible" electrochemical derivatization; and iii) in situ mechanistic study and capture of key radical intermediates when coupled with mass spectrometry.

Two-step reaction mechanism reveals new antioxidant capability of cysteine disulfides against hydroxyl radical attack

Cysteine disulfides, which constitute an important component in biological redox buffer systems, are highly reactive toward the hydroxyl radical (^•OH). The mechanistic details of this reaction, however, remain unclear, largely due to the difficulty in characterizing unstable reaction products. Herein, we have developed a combined approach involving mass spectrometry (MS) and theoretical calculations to investigate reactions of ^•OH with cysteine disulfides (Cys-S-S-R) in the gas phase. Four types of first-generation products were identified: protonated ions of the cysteine thiyl radical (⁺Cys-S^•), cysteine (⁺Cys-SH), cysteine sulfinyl radical (⁺Cys-SO^•), and cysteine sulfenic acid (⁺Cys-SOH). The relative reaction rates and product branching ratios responded sensitively to the electronic property of the R group, providing key evidence to deriving a two-step reaction mechanism. The first step involved ^•OH conducting a back-side attack on one of the sulfur atoms, forming sulfenic acid (-SOH) and thiyl radical (-S^•) product pairs. A subsequent H transfer step within the product complex was favored for protonated systems, generating sulfinyl radical (-SO^•) and thiol (-SH) products. Because sulfenic acid is a potent scavenger of peroxyl radicals, our results implied that cysteine disulfide can form two lines of defense against reactive oxygen species, one using the cysteine disulfide itself and the other using the sulfenic acid product of the conversion of cysteine disulfide. This aspect suggested that, in a nonpolar environment, cysteine disulfides might play a more active role in the antioxidant network than previously appreciated.

A New Quantification Method Using Electrochemical Mass Spectrometry

Mass spectrometry-based quantification method has advanced rapidly. In general, the methods for accurate quantification rely on the use of authentic target compounds or isotope-labeled compounds as standards, which might be not available or difficult to synthesize. To tackle this grand challenge, this paper presents a novel approach, based on electrochemistry (EC) combined with mass spectrometry (MS). In this approach, a target compound is allowed to undergo electrochemical oxidation and then subject to MS analysis. The oxidation current recorded from electrochemistry (EC) measurement provides information about the amount of the oxidized analyte, based on the Faraday's Law. On the other hand, the oxidation reaction yield can be determined from the analyte MS signal changes upon electrolysis. Therefore, the total amount of analyte can be determined. In combination with liquid chromatography (LC), the method can be applicable to mixture analysis. The striking strength of such a method for quantitation is that neither standard compound nor calibration curve is required. Various analyte molecules such as dopamine, norepinephrine, and rutin as well as peptide glutathione in low quantity were successfully quantified using our method with the quantification error ranging from - 2.6 to + 4.6%. Analyte in a complicated matrix (e.g., uric acid in urine) was also accurately measured. Graphical Abstract.

Regioselective 5'-position phosphorylation of ribose and ribonucleosides: phosphate transfer in the activated pyrophosphate complex in the gas phase

Herein, we present a rapid, efficient and regioselective phosphorylation method at the 5'-position of unprotected ribose and ribonucleosides with pyrophosphate in the gas phase, which involves the formation of anionic complexes via electrospray ionization and collisional activation to induce phosphorylation within the complexes.

Microdroplets as Microreactors for Fast Synthesis of Ketoximes and Amides

The formation of amide bonds is one of the most valuable transformations in organic synthesis. Beckmann rearrangement is a well-known method for producing secondary amides from ketoximes. This study demonstrates the rapid synthesis of ketoximes and amides in microdroplets. Many factors are found to affect the yield, such as microdroplet generation devices, temperature, catalysts, and concentrations of reactants. In particular, the temperature has a great influence on the synthesis of amide, which is demonstrated by a sharp ascendance to the yield when the temperature was increased to 45 °C. The best amide yield (93.3%) can be obtained by using coaxial flowing devices, a sulfonyl chloride compound as a catalyst, and heating to 55 °C in microdroplets. The yields can reach 78.7-91.3% for benzoylaniline and 87.2-93.4% for benzophenone oximes in several seconds in microdroplets compared to 10.1-66.1% and 82.5-93.3% in several hours in the bulk phase. Apart from the dramatically decreased reaction time and enhanced reaction yields, the microdroplet synthesis is also free of severe reaction environments (anhydrous and anaerobic conditions). In addition, the synthesis in microdroplets also saves reactants and solvents and reduces the waste amounts. All of these merits indicate that the microdroplet synthesis is a high-efficiency green methodology.

Ta2 +-mediated ammonia synthesis from N2 and H2 at ambient temperature

In a full catalytic cycle, bare Ta₂ ⁺ in the highly diluted gas phase is able to mediate the formation of ammonia in a Haber-Bosch-like process starting from N₂ and H₂ at ambient temperature. This finding is the result of extensive quantum chemical calculations supported by experiments using Fourier transform ion cyclotron resonance MS. The planar Ta₂N₂ ⁺, consisting of a four-membered ring of alternating Ta and N atoms, proved to be a key intermediate. It is formed in a highly exothermic process either by the reaction of Ta₂ ⁺ with N₂ from the educt side or with two molecules of NH₃ from the product side. In the thermal reaction of Ta₂ ⁺ with N₂, the N≡N triple bond of dinitrogen is entirely broken. A detailed analysis of the frontier orbitals involved in the rate-determining step shows that this unexpected reaction is accomplished by the interplay of vacant and doubly occupied d-orbitals, which serve as both electron acceptors and electron donors during the cleavage of the triple bond of N≡N by the ditantalum center. The ability of Ta₂ ⁺ to serve as a multipurpose tool is further shown by splitting the single bond of H₂ in a less exothermic reaction as well. The insight into the microscopic mechanisms obtained may provide guidance for the rational design of polymetallic catalysts to bring about ammonia formation by the activation of molecular nitrogen and hydrogen at ambient conditions.