AB Dehydrogenation Research Articles

In situ synthesized Ag nanoparticles encapsulated inside carbonized ZIF-8 for efficient Cr(VI) reduction

Effective reduction of carcinogenic contaminant Cr(VI) to low-toxic Cr(III) is of global importance for environmental and water source protection. Herein, a stable metal-organic framework (MOF), ZIF-8, was carbonized as a template to synthesize a novel nanocomposite involving Ag nanoparticles (NPs) inside (Ag@C-ZIF-8). Surprisingly, the Ag NPs synthesized in situ in the Ag+@C-ZIF-8/AB system exhibited outstanding reduction ability toward Cr(VI) and eliminated 100 % of Cr(VI) (20 mg/L) within 10 min in an initial pH range of 3–5. The Cr(VI) removal efficiency was much higher compared with these systems of AB (25.5 %), C-ZIF-8/AB (44.6 %), Ag+/AB (66.8 %), and Ag@C-ZIF-8/AB (39.3 %). Increasing the initial pH of the solution and the amount of C-ZIF-8 template accelerated Cr(VI) reduction. In four cycles of experiments, over 92 % of Cr(VI) was reduced without any treatment, demonstrating the excellent stability and reusability of Ag@C-ZIF-8. X-ray photoelectron spectroscopy (XPS) characterization and mechanism exploration experiments indicated that Ag NPs catalyzed AB dehydrogenation and efficiently reduced Cr(VI) together with the generated hydrogen. This is the first report on carbonized MOF-based Ag NPs synthesized in situ for Cr(VI) reduction by combining catalytic AB dehydrogenation with metal nanoparticle reducibility. This work provides new avenues for the utilization of heavy metal ions in water environments and the development of novel and efficient reductants/catalysts of Cr(VI) removal.

Cu2O/UiO-66-NH2 composite photocatalysts for efficient hydrogen production from ammonia borane hydrolysis

Ammonia borane (NH3BH3, AB) is a chemical hydride with a high hydrogen capacity of 19.6 wt%, which makes it a promising hydrogen carrier. Cuprous oxide (Cu2O) is one of the most active photocatalysts for AB dehydrogenation at ambient conditions. However, the instability due to photocorrosion and high charge recombination are the main drawbacks of practical application. In this work, Cu2O is coupled with a metal-organic framework (MOF) as a composite photocatalyst (Cu2O/UiO-66-NH2), which demonstrates a better photocatalytic performance in AB hydrolysis than its pure counterpart samples because of the heterojunction configuration. The Z-scheme charge transfer pathway in Cu2O/UiO-66-NH2 composite can improve charge separation, hydrogen production efficiency, photocatalyst stability, and reduce activation energy. The optimum composite photocatalyst comprising 50 wt% Cu2O loading shows the highest hydrogen evolution yield of almost 2.3 equivalent H2 from AB hydrolysis.

Enhanced Effect of an External Electric Field on NH3BH3 Dehydrogenation: an AIMD Study for Thermolysis.

How to improve the dehydrogenation properties of ammonia borane (AB, NH3BH3) is always a challenge for its practical application in hydrogen storage. In this study, we reveal the enhanced effect of an external electric field (Eext) on AB dehydrogenation by means of the ab initio molecular dynamics method. The molecular rotation induced by an electrostatic force can facilitate the formation of the H–N···B–H framework, which would aggregate into poly-BN species and further suppress the generation of the volatile byproducts. Meanwhile, the dihydrogen bond (N–Hδ+···δ−H–B) is favorably formed under Eext, and the interaction between relevant H atoms is enhanced, leading to a faster H2 liberation. Correspondingly, the apparent activation energy for AB dissociation is greatly reduced from 18.42 to around 15 kcal·mol–1 with the application of an electric field, while that for H2 formation decreases from 20.4 to about 16 kcal·mol–1. In the whole process, the cleavage of the B–H bond is more favorable than that of the N–H bond, no matter whether the application of Eext. Our results give a deep insight into a positive effect of an electric field on AB dehydrogenation, which would provide an important inspiration for hydrogen storage in industry applications.

Design and Development of Ruthenium-Based Catalysts for Enabling Hydrogen Storage

For past decades, hydrocarbon-based fuels have been the primary source of energy as a necessity for modern machines and automotive vehicles. Despite use in combustion engines and power plants, fossil fuels reserves are unpredictable and the associated CO2 emissions are now causing terrible effects on the environment and human health. Researchers have realized H2 as a potentially safe and efficient energy source, with an energy density of 33.3 kWh per kg. Moreover, H2 is significantly more environmentally friendly as H2O is the only by-product. Currently, the development of on-board storage technology is progress for use in the transportation industry. The chemical storage of hydrogen, in which H2 is bound to a carrier molecule, provides a more practical and safer method to store and release immense amounts of H2. Ammonia Borane (H3N-BH3, AB) is a useful material for storing up to 19.6 wt% of and 0.145kg L-1 of H2 with the ability to release H2 under mild ambient conditions through exposure to a suitable catalyst. This project investigates the use of pyrazole-based compounds as ligands for η6-arene Ru-complexes in order to formulate efficient catalysts for AB dehydrogenation. Pyrazoles are interesting diaza-five member heterocycles and have strong electron-donating properties. Mono- and di-coordinating substituted pyrazole complexes and an unusual Cl-bridging dimeric Ru complex were successfully synthesized and characterized (NMR, ESI-MS and X-ray diffraction crystallography) before undergoing evaluation for AB dehydrogenation studies in a high-pressure stainless steel reactor. The dimeric Ru Cl-bridging catalyst released the largest H2 equivalent per mol of AB with 1.45 with a total of 7.82 bar of H2 pressure, proving to be the most successful catalyst in the series. However, from the H2 release profiles, it appears that catalysts undergo slow transformation where it is possible that the pyrazole ligands are lost. Further mechanistic studies are required to determine the decomposition process.

An efficient single atom catalysts Os/P3C sheet for ammonia borane dehydrogenation

Ammonia borane (NH3BH3, AB) has been considered to be a promising chemical hydrogen storage material. Based on density functional theory, a series of transition metal atoms supported P3C (P3C_O) sheet is systematically investigated to screen out the most promising catalyst for dehydrogenation of AB. The results indicate that the Os/P3C and Os/P3C_O could be an efficient single atom catalyst (SACs) and the stepwise reaction pathway with free energy barrier of 2.07 and 1.54 eV respectively. Remarkably, the rate constant further quantitatively confirmed the real situation of the first step of dehydrogenation of AB on the Os/P3C and Os/P3C_O substrates. We found that kf1 at 400 K is equivalent to kf2 at 800 K, which greatly improves the temperature of the first step of AB dehydrogenation on P3C_O. We hope this work can provide a promising method for the design of catalysts for AB dehydrogenation reactions on the surface of two-dimensional materials (2D).

Ammonia-Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes.

Metal complexes incorporating proton-responsive ligands have been proved to be superior catalysts in reactions involving the H2 molecule. In this contribution, a series of IrIII complexes based on lutidine-derived CNNH pincers containing N-heterocyclic carbene and secondary amino NHR [R = Ph (4a), tBu (4b), benzyl (4c)] donors as flanking groups have been synthesized and tested in the dehydrogenation of ammonia–borane (NH3BH3, AB) in the presence of substoichiometric amounts (2.5 equiv) of tBuOK. These preactivated derivatives are efficient catalysts in AB dehydrogenation in THF at room temperature, albeit significantly different reaction rates were observed. Thus, by using 0.4 mol % of 4a, 1.0 equiv of H2 per mole of AB was released in 8.5 min (turnover frequency (TOF50%) = 1875 h–1), while complexes 4b and 4c (0.8 mol %) exhibited lower catalytic activities (TOF50% = 55–60 h–1). 4a is currently the best performing IrIII homogeneous catalyst for AB dehydrogenation. Kinetic rate measurements show a zero-order dependence with respect to AB, and first order with the catalyst in the dehydrogenation with 4a (−d[AB]/dt = k[4a]). Conversely, the reaction with 4b is second order in AB and first order in the catalyst (−d[AB]/dt = k[4b][AB]2). Moreover, the reactions of the derivatives 4a and 4b with an excess of tBuOK (2.5 equiv) have been analyzed through NMR spectroscopy. For the former precursor, formation of the iridate 5 was observed as a result of a double deprotonation at the amine and the NHC pincer arm. In marked contrast, in the case of 4b, a monodeprotonated (at the pincer NHC-arm) species 6 is observed upon reaction with tBuOK. Complex 6 is capable of activating H2 reversibly to yield the trihydride derivative 7. Finally, DFT calculations of the first AB dehydrogenation step catalyzed by 5 has been performed at the DFT//MN15 level of theory in order to get information on the predominant metal–ligand cooperation mode.

Surface property and spatial confinement engineering for achieving Ru nanoclusters on O/N-doped hollow carbon towards enhanced hydrogen production

Supported metal nanoclusters (NCs) have become highly attractive in catalytic applications because of their maximum atom utilization with superior catalytic property. The main challenge in fabricating metal NC catalysts is their low binding strength with carriers, which induces transformation of metal NCs to large nanoparticles. In this study, a facile, effective, and eco-friendly synthetic strategy for O/N-doped hollow carbon (ONC) is developed through direct steaming commercial Vulcan carbon in nitric acid vapour. The strong binding strength between abundant O/N functional groups of hollow structure of carbon matrix and Ru precursors enables the production of highly dispersed Ru NCs on ONC (Ru/ONC). The achieved Ru/ONC with highly distributed Ru NCs (1.69 nm in diameter) exhibits a significant activity improvement for catalytic AB dehydrogenation compared with Ru/C without modification. High turnover frequencies of 556 and 1837 min−1 (with NaOH) are achieved under the optimal conditions, surpassing most of previous developed Ru catalysts. Homogenously distributed Ru NCs with rich surface-active sites and the O/N functional groups of hollow structured carbon induced fast mass transfer are responsible for the superior activity. The facile strategy shows great application prospects for the preparation of efficient supported metal catalysts by modifying the structure and surface properties of carbon carriers.

Effect of maleic acid on onset temperature and H2 release kinetics for thermal dehydrogenation of ammonia borane

Ammonia borane (AB, NH3BH3) has received great attention as an attractive hydrogen storage candidate because it has high hydrogen contents and releases hydrogen under mild operating conditions. Despite the favorable properties, AB thermolysis has several drawbacks such as long induction period, slow kinetics, and relatively high onset temperature, compared to hydrolysis approach. In this study, hydrogen release properties from AB were investigated in the addition of maleic acid (C4H4O4, MA). Using thermogravimetric analysis, temperature programmed reaction with mass spectrometry, and FTIR analyses, the solid and gaseous products generated by thermolysis of the AB-MA mixture were characterized to understand the reaction mechanism. It was found that with the addition of MA, hydrogen yield and release kinetics were enhanced, while the onset temperature reduced significantly to ~60 °C. It is likely that the hydrolysis between O–H bonds in MA and B–H bonds in AB was initiated, and the heat released from the hydrolysis triggers the thermolysis of AB. It was also confirmed that a combination of the two additives (MA and boric acid) enables a further increase of H2 yield while the onset temperature remains at ~60 °C. Our results suggest that MA is a promising additive to improve AB dehydrogenation.

Recent Advances in Noble Metal Catalysts for Hydrogen Production from Ammonia Borane

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.

Complexation of Ammonia Boranes with Al3.

Ammonia borane, NH3BH3 (AB), is very attractive for hydrogen storage; however, it dehydrogenates exothermally, producing a mixture of polymeric products with limited potential for direct rehydrogenation. Recently, it was shown that AB complexed with Al3+ in Al(BH4)3·AB endothermically dehydrogenates to a single product identified as Al(BH4)3·NHBH, with the potential for direct rehydrogenation of AB. Here we explore the reactivity of AB-derived RNH2BH3 (R = -CH3, -CH2-) with AlX3 salts (X = BH4-, Cl-), aiming to extend the series to different anions and to enlarge the stability window for Al(BH4)3·NRBH. Three novel complexes were identified: Al(BH4)3·CH3NH2BH3 having a molecular structure similar to that of Al(BH4)3·AB but different dehydrogenation properties, as well as [Al(CH3NH2BH3)2Cl2][AlCl4] and [Al(NH2CH2CH2NH2)(BH4)2][Al(BH4)4], rare examples of Al3+ making part of the cations and anions simultaneously. The latter compounds are of interest in the design of novel electrolytes for Al-based batteries. The coordination of two ABs to a single Al atom opens a route to materials with higher hydrogen content.

The Onset of Dehydrogenation in Solid Ammonia Borane: An Ab Initio Metadynamics Study.

The discovery of effective hydrogen storage materials is fundamental for the progress of a clean energy economy. Ammonia borane (H3 BNH3 , AB) has attracted great interest as a promising candidate but the reaction path that leads from its solid phase to hydrogen release is not yet fully understood. To address the need for insights in the atomistic details of such a complex solid state process, in this work we use ab-initio molecular dynamics and metadynamics to study the early stages of AB dehydrogenation. We show that the formation of ammonia diborane (H3 NBH2 (μ-H)BH3 ) leads to the release of NH4 + , which in turn triggers an autocatalytic H2 production cycle. Our calculations provide a model for how complex solid state reactions can be theoretically investigated and rely upon the presence of multiple ammonia borane molecules, as substantiated by standard quantum-mechanical simulations on a cluster.

The Onset of Dehydrogenation in Solid Ammonia Borane: An Ab Initio Metadynamics Study

AbstractThe discovery of effective hydrogen storage materials is fundamental for the progress of a clean energy economy. Ammonia borane (H3BNH3, AB) has attracted great interest as a promising candidate but the reaction path that leads from its solid phase to hydrogen release is not yet fully understood. To address the need for insights in the atomistic details of such a complex solid state process, in this work we use ab‐initio molecular dynamics and metadynamics to study the early stages of AB dehydrogenation. We show that the formation of ammonia diborane (H3NBH2(μ‐H)BH3) leads to the release of NH4+, which in turn triggers an autocatalytic H2 production cycle. Our calculations provide a model for how complex solid state reactions can be theoretically investigated and rely upon the presence of multiple ammonia borane molecules, as substantiated by standard quantum‐mechanical simulations on a cluster.

Influence of Metal–Organic Framework Porosity on Hydrogen Generation from Nanoconfined Ammonia Borane

Hydrogen released from chemical hydride ammonia borane (AB, NH3BH3) can be greatly improved when AB is confined in metal–organic frameworks (MOFs), showing reduced decomposition temperature and suppressed unwanted byproducts. However, it is still debatable whether the mechanism of improved AB dehydrogenation is due to catalysis or nanosize. In this research, selected MOFs (IRMOF-1, IRMOF-10, UiO-66, UiO-67, and MIL-53(Al)) were chosen to explore both catalytic effect of the metal clusters and the manipulation of pore size for nanoconfinement by variations in ligand length. When AB particle size was restricted by the controlled micropores of MOFs, we observed that the decomposition temperature was not correlated to the MOF catalytic environment, but inversely proportional to the reciprocal of the particle size. The results correspond well with the derived thermodynamic model for AB decomposition considering surface tension of nanoparticles.

Low-cost CuNi-CeO2/rGO as an efficient catalyst for hydrolysis of ammonia borane and tandem reduction of 4-nitrophenol

Low-cost metallic nanoparticles as catalysts with good performance are highly desired for the development of hydrogen storage materials. In this work, ceria-doped CuNi nanoparticles were successfully immobilized on the surfaces of reduced graphene oxide (rGO) by a simple co-reduction approach in aqueous solution at room temperature, characterized by ICP-OES, XRD, TEM, SEM-EDS and XPS techniques. The as-synthesized CuNi-CeO2/rGO nanocomposites with various metal contents had been employed as heterogeneous catalysts for the hydrolytic dehydrogenation of ammonia borane (NH3BH3, AB) under mild conditions. The optimal catalyst of Cu0.8Ni0.2-CeO2/rGO with CeO2 content of 13.9 mol% exhibited an excellent catalytic activity with the exceedingly high TOF value of 34.4·molH2·molcatalyst−1·min−1 at 298 K. The apparent activation energy was calculated to be 19.1 kJ mol−1, even lower than most of noble-metal-based catalysts for AB dehydrogenation. The detailed kinetics of AB hydrolysis catalyzed by Cu0.8Ni0.2-CeO2/rGO had been investigated on different concentrations of catalyst, substrate and temperatures. Moreover, the obtained in situ hydrogen from AB hydrolysis can be further applied to reduce 4-nitrophenol with a high TOF value of 8.1 min−1 at room temperature. The high catalytic activity of Cu0.8Ni0.2-CeO2/rGO would be contributed to the small size of CuNi-CeO2 NPs, metal-metal synergy, and the metal-support interaction.

Ammonia Borane Dehydrogenation Catalyzed by (κ4-EP3)Co(H) [EP3 = E(CH2CH2PPh2)3; E = N, P] and H2 Evolution from Their Interaction with NH Acids.

Two Co(I) hydrides containing the tripodal polyphosphine ligand EP3, (κ4-EP3)Co(H) [E(CH2CH2PPh2)3; E = N (1), P (2)], have been exploited as ammonia borane (NH3BH3, AB) dehydrogenation catalysts in THF solution at T = 55 °C. The reaction has been analyzed experimentally through multinuclear (11B, 31P{1H}, 1H) NMR and IR spectroscopy, kinetic rate measurements, and kinetic isotope effect (KIE) determination with deuterated AB isotopologues. Both complexes are active in AB dehydrogenation, albeit with different rates and efficiency. While 1 releases 2 equiv of H2 per equivalent of AB in ca. 48 h, with concomitant borazine formation as the final "spent fuel", 2 produces 1 equiv of H2 only per equivalent of AB in the same reaction time, along with long-chain poly(aminoboranes) as insoluble byproducts. A DFT modeling of the first AB dehydrogenation step has been performed, at the M06//6-311++G** level of theory. The combination of the kinetic and computational data reveals that a simultaneous B-H/N-H activation occurs in the presence of 1, after a preliminary AB coordination to the metal center. In 2, no substrate coordination takes place, and the process is better defined as a sequential BH3/NH3 insertion process on the initially formed [Co]-NH2BH3 amidoborane complex. Finally, the reaction of 1 and 2 with NH-acids [AB and Me2NHBH3 (DMAB)] has been followed via VT-FTIR spectroscopy (in the -80 to +50 °C temperature range), with the aim of gaining a deeper experimental understanding of the dihydrogen bonding interactions that are at the origin of the observed H2 evolution.

Non-Noble-Metal Nanoparticle Supported on Metal-Organic Framework as an Efficient and Durable Catalyst for Promoting H2 Production from Ammonia Borane under Visible Light Irradiation.

In this work, we propose a straightforward method to enhance the catalytic activity of AB dehydrogenation by using non-noble-metal nanoparticle supported on chromium-based metal-organic framework (MIL-101). It was demonstrated to be effective for hydrogen generation from ammonia borane under assistance of visible light irradiation as a noble-metal-free catalyst. The catalytic activity of metal nanoparticles supported on MIL-101 under visible light irradiation is remarkably higher than that without light irradiation. The TOFs of Cu/MIL-101, Co/MIL-101, and Ni/MIL-101 are 1693, 1571, and 3238 h(-1), respectively. The enhanced activity of catalysts can be primarily attributed to the cooperative promoting effects from both non-noble-metal nanoparticles and photoactive metal-organic framework in activating the ammonia borane molecule and strong ability in the photocatalytic production of hydroxyl radicals, superoxide anions, and electron-rich non-noble-metal nanoparticle. This work sheds light on the exploration of active non-noble metals supported on photoactive porous materials for achieving high catalytic activity of various redox reactions under visible light irradiation.

A novel dehydrogenation style of NH3BH3 by catalyst of transition metal clusters

The dehydrogenation of ammonia-borane (NH3BH3, AB) by transition metal (TM) catalyst has been under intense scrutiny in experiments but a sound molecular level understanding has remained elusive. Herein, using the density functional theory (DFT) method, AB dehydrogenation mechanistic routes underscores the importance of formations of metal-dihydrogen intermediate in the presence of Cu2, Fe2, FeCu dimers and Fe12 Cu cluster. Its formation involves the stepwise or concerted transfer of H(B) and H(N) hydrogen atoms from AB to metal atom, which is different from the previously proposed dehydrogenation mechanism that one H(N) hydrogen atom is firstly transferred to B atom and then the polymerized H2 molecule is released from B atom. The metal-dihydride Cu2 H2 rather than the dissociated H2 is ultimately derived for the catalytic reaction between Cu2 and AB. Nevertheless, with respect to the dehydrogenation of pristine AB, the release of one equiv of H2 molecule per AB can be significantly promoted in a kinetically fast and thermodynamically favorable way by the catalysts of Fe2, FeCu, and Fe12 Cu.

Dehydrogenation of ammonia-borane by cationic Pd(II) and Ni(II) complexes in a nitromethane medium: hydrogen release and spent fuel characterization.

A highly electrophilic cationic Pd(II) complex, [Pd(MeCN)4][BF4]2 (1), brings about the preferential activation of the B-H bond in ammonia-borane (NH3·BH3, AB). At room temperature, the reaction between 1 in CH3NO2 and AB in tetraglyme leads to Pd nanoparticles and formation of spent fuels of the general formula MeNHxBOy as reaction byproducts, while 2 equiv. of H2 is efficiently released per AB equiv. at room temperature within 60 seconds. For a mechanistic understanding of dehydrogenation by 1, the chemical structures of spent fuels were intensely characterized by a series of analyses such as elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), solid state magic-angle-spinning (MAS) NMR spectra ((2)H, (13)C, (15)N, and (11)B), and cross polarization (CP) MAS methods. During AB dehydrogenation, the involvement of MeNO2 in the spent fuels showed that the mechanism of dehydrogenation catalyzed by 1 is different from that found in the previously reported results. This AB dehydrogenation derived from MeNO2 is supported by a subsequent digestion experiment of the AB spent fuel: B(OMe)3 and N-methylhydroxylamine ([Me(OH)N]2CH2), which are formed by the methanolysis of the AB spent fuel (MeNHxBOy), were identified by means of (11)B NMR and single crystal structural analysis, respectively. A similar catalytic behavior was also observed in the AB dehydrogenation catalyzed by a nickel catalyst, [Ni(MeCN)6][BF4]2 (2).

CoPd alloy nanoparticles catalyzed tandem ammonia borane dehydrogenation and reduction of aromatic nitro, nitrile and carbonyl compounds

Addressed herein is a general and facile route for the reduction of aromatic nitro, nitrile, and carbonyl compounds to the corresponding primary amines and alcohols, respectively, under ambient conditions. Our reduction approach comprises the tandem AB dehydrogenation and hydrogenation of unsaturated organic groups catalyzed by reduced graphene oxide supported Co30Pd70 alloy nanoparticles (rGO-Co30Pd70) in water/methanol mixture (v/v=7/3) at room temperature. Monodisperse Co30Pd70 alloy NPs were synthesized by using an organic solution phase protocol involving the co-reduction of cobalt(II) acetylacetonate and palladium(II) acetylacetonate in oleylamine and borane-tert-butylamine mixture at 100°C. The colloidal Co30Pd70 NPs were assembled on reduced graphene oxide (rGO-Co30Pd70) before their use as catalysts in the tandem reactions. A variety of aromatic nitro, nitriles, and carbonyl compounds were tested by the rGO-Co30Pd70 catalyzed tandem reaction and all the corresponding primary amines or alcohols were obtained by the yields reaching up to 99% within reaction times of 5–15min.

Chemical Hydrogen Storage: Ammonia Borane Dehydrogenation Catalyzed by NP3Ruthenium Hydrides (NP3=N(CH2CH2PPh2)3)

Two novel RuII hydrides containing the tripodal polyphosphine ligand NP3 (N(CH2CH2PPh2)3) have been prepared and characterized: (κ4-NP3)Ru(H)2 (1) and [(κ4-NP3)Ru(H)(η2-H2)]BArCl4 (2; ArCl=3,5-dichlorophenyl, C6H3Cl2). The classical and nonclassical nature of the hydride ligand in 1 and 2, respectively, has been confirmed by solution NMR studies and single-crystal X-ray diffraction. The reaction of 1 and 2 with excess ammonia borane (NH3⋅BH3, AB) has been analyzed experimentally through variable-temperature multinuclear (11B, 31P, 1H) NMR spectroscopy, kinetic rate measurements, and kinetic isotope effect determination with deuterated AB isotopologues. Both complexes are active in AB dehydrogenation, with release of two H2 equivalents per AB equivalent, with concomitant polyborazylene and cyclic polyaminoborane formation as the final “spent fuel”. A DFT modeling of the AB first dehydrogenation step has been finally performed, at the M06//6-31G* level of theory. The combination of the kinetic and computational data reveals that the initial AB activation step is different for the two catalysts: a simultaneous BH/NH activation occurs in the presence of 1, whereas the NH activation only is the rate-determining step if 2 is employed as a catalyst.