Hydride Complexes Research Articles

Synthesis and catalysis of diruthenium hydride complexes with bidentate dimethylsulfoxide ligand

A new, simple and controllable synthetic route is established to one-step synthesize diruthenium complexes with μ -H, μ -Cl halogen and μ -S,O-dmso bridges, namely (Bu4N)[Ru2(μ -H)(μ -X)(μ -S,O-dmso)(S-dmso)3(Cl)3] (Bu4N·1, where dmso = dimethyl sulfoxide) in one step. This complex is obtained by treating [Ru(dmso)4Cl2] with Bu4NCl in presence of excess Et3N in refluxing methanol. Advantages over prior routes to these analogous complexes lie in one-step controllable synthesis, and the short reaction times under experimentally convenient conditions. The properties of Bu4N·1 in solution and in solid-state are investigated. In addition, the catalytic performance of Bu4N·1 for CO2 + H2 / HCOO– interconversion in aqueous solution is also described.

Reductive C-O Cleavage of Ethereal Solvents and 18-Crown-6 in Ln(NR2)3/KC8 Reactions (R = SiMe3).

The high reactivity accessible from the reduction of the tris(amide) complexes Ln(NR2)3 (R = SiMe3) with potassium graphite in the presence of a variety of ethers is demonstrated by crystal structures of six different types of products of C-O bond cleavage reactions with Ln = Y, Ho, Er, and Lu. Specifically, 1,2-dimethoxyethane (DME) can be cleaved in Ln(NR2)3/KC8 reactions as shown by three different types of crystals: [K (crypt)][(R2N)3Y(OCH2CH2OCH3)], 1-Y, [(R2N)2Y(μ-OCH2CH2OCH3-κO,κO')]2, 2-Y, and [K2(18-c-6)3]{[(R2N)3Lu]2[(μ-OCH2CH2O)]}, 3-Lu (18-c-6 = 18-crown-6; crypt = 2.2.2-cryptand). THF can be ring opened by the Y(NR2)3/KC8 reaction system, as shown by crystals of the butoxide, [K(crypt)][(R2N)3Y(OCH2CH2CH2CH3)], 4-Y. The cyclic ether, oxetane, OC3H6, ring opens in Ln(NR2)3/KC8 reactions to form crystals of the propoxide, [K(18-c-6)(OC3H6)][(R2N)3Ln(OCH2CH2CH3)], 5-Ln, for Ln = Ho and Er. In Et2O, the Y(NR2)3/KC8 reactions do not attack the solvent, but C-O cleavage of 18-c-6 is observed to form {[(R2N)2]Y[μ-η1:η1-O2(C10H20O4)K]}2, 6-Y. These Ln(NR2)3/KC8 C-O cleavage reactions are typically accompanied by C-H bond activation reactions, which form cyclometalates such as [K(crypt)]{(R2N)2Ln[N(SiMe3)(SiMe2CH2)-κC,κN]}, 7-Ln (Ln = Y, Ho, Er), and [K(18-c-6)]{(R2N)2Y[N(SiMe3)(SiMe2CH2)-κC,κN]}, 8-Y, which are common decomposition products of Ln(NR2)3 reactions. In addition, in this study, the hydride complex, [K(18-c-6)][(R2N)3YH], 9-Y, was isolated. NMR analysis indicates that the yttrium reactions form mixtures that consistently contain the yttrium cyclometalates 7-Y and 8-Y as major components. These results show the diversity of available reaction pathways for the Ln(NR2)3/KC8 system and highlight the inherent difficulties in isolating Ln(II) complexes containing the [Ln(NR2)3]1- anion.

Catalytic, Z-Selective, Semi-Hydrogenation of Alkynes with a Zinc–Anilide Complex

The reversible activation of dihydrogen with a molecular zinc anilide complex is reported. The mechanism of this reaction has been probed through stoichiometric experiments and density functional theory (DFT) calculations. The combined evidence suggests that H2 activation occurs by addition across the Zn-N bond via a four-membered transition state in which the Zn and N atoms play a dual role of Lewis acid and Lewis base. The zinc hydride complex that results from H2 addition has been shown to be remarkably effective for the hydrozincation of C═C bonds at modest temperatures. The scope of hydrozincation includes alkynes, alkenes, and a 1,3-butadiyne. For alkynes, the hydrozincation step is stereospecific leading exclusively to the syn-isomer. Competition experiments show that the hydrozincation of alkynes is faster than the equivalent alkene substrates. These new discoveries have been used to develop a catalytic system for the semi-hydrogenation of alkynes. The catalytic scope includes both aryl- and alkyl-substituted internal alkynes and proceeds with high alkene: alkane, Z:E ratios, and modest functional group tolerance. This work offers a first example of selective hydrogenation catalysis using zinc complexes.

Catalytic transformation of 4-nitrophenol into 4-aminophenol over ZnO nanowire array-decorated Cu nanoparticles

To realize economical and effective removal of hazardous 4-nitrophenol from the environment, we developed an easily recyclable ZnO nanowire array decorated with Cu nanoparticles. Its salix argyracea-shaped structure not only provides a platform to achieve stable and good dispersion of Cu nanoparticles, but also offers a great deal of catalytically active sites. The density functional theory calculations reveal that ZnO and Cu have a very beneficial synergistic effect on their catalytic capability. This synergy is ascribed to the electronic localization occurring at ZnO/Cu interface, which helps improve Cu nanoparticle's ability to adsorb electro-negatively 4-nitrophenolate ions and to capture hydrogen radicals, thereby accelerating the hydrogen transfer from metal hydride complex to 4-nitrophenol. Benefiting from these characteristics, it exhibits high efficiency and reusability towards the catalytic reduction of waste 4-nitrophenol to valuable 4-aminophenol with a rate constant of 43.02 × 10−3 s−1 and an average conversion of 96.5% in 90 s during 10 cycles. This activity is superior to that of most reported noble- or non-noble-metal powder, bulk, coating, and array catalysts, indicating its competitive advantages in cost and efficiency, as well as enticing application prospects.

Hirshfeld Atom Refinement of Metal-Organic Complexes: Treatment of Hydrogen Atoms Bonded to Transition Metals.

Hydrogen positions in hydrides play a key role in hydrogen storage materials and high-temperature superconductors. Our recently published study of five crystal structures of transition-metal-bound hydride complexes showed that using aspherical atomic scattering factors for Hirshfeld atom refinement (HAR) resulted in a systematic elongation of metal-hydrogen bonds compared to using spherical scattering factors with the Independent Atom Model (IAM). Even though only standard-resolution X-ray data was used, for the highest-quality data, we obtained excellent agreement between the X-ray and the neutron-derived bond lengths. We present an extended version of this study including 10 crystal structures of metal-organic complexes containing hydrogen atoms bonded to transition-metal atoms for which both X-ray and neutron data are available. The neutron structures were used as a benchmark, and the X-ray structures were refined by applying Hirshfeld atom refinement using various basis sets and DFT functionals in order to investigate the influence of the technical aspects on the length of metal-hydrogen bonds. The result of including relativistic effects in the Hamiltonian and using a cluster of multipoles simulating interactions with a crystal environment during wave function calculations was examined. The effect of the data quality on the final result was also evaluated. The study confirms that a high quality of experimental data is the key factor allowing us to obtain significant improvement in transition metal (TM)-hydrogen bond lengths from HAR in comparison with the IAM. Individual adjustments and better choices of the basis set can improve hydrogen positions. Average differences between TM-H bond lengths obtained with various DFT functionals upon including relativistic effects or between double-ζ and triple-ζ basis sets were not statistically significant. However, if all bonds formed by H atoms were considered, significant differences caused by different refinement strategies were observed. Finally, we examined the refinement of atomic thermal motions. Anisotropic refinement of hydrogen thermal motions with HAR was feasible only in some cases, and isotropically refined hydrogen thermal motions were in similar agreement with neutron values whether obtained with HAR or with the IAM.

Crystal structure and DFT calculations of Cp2NbH(SiIMe2)(SiFMe2): an asymmetric bis(silyl) niobocene hydride complex.

An asymmetric bis(silyl) niobocene hydride complex, namely, bis(η5-cyclopentadienyl)(fluorodimethylsilyl)hydrido(iododimethylsilyl)niobium, [Nb(C5H5)2(C2H6FSi)(C2H6ISi)H] or Cp2NbH(SiIMe2)(SiFMe2), has been studied to determine the effect of the silyl ligand on the position of the hydride attached to the Nb atom. It has been shown that when a Group 17 atom is substituted onto one of the silyl ligands, there is a greater interaction between the hydride and this ligand, as demonstrated by a shorter Si...H distance. In the present work, we have investigated the effect when the silyl ligands are substituted by different Group 17 atoms. We present here the structure and DFT calculations of Cp2NbH(SiIMe2)(SiFMe2), showing that the position of the hydride is located between the two silyl ligands. The results from our investigation show that the hydride is closer to the silyl ligand that is substituted by fluorine.

Evaluating the Catalytic Activities of PNCNP Pincer Group 10 Metal Hydride Complexes: Pd-Catalyzed Reduction of CO2 to the Formic Acid Level with NH3·BH3 and NaBH4 under Ambient Conditions.

In order to develop efficient protocols for CO2 reduction with less expensive and more convenient hydrogen sources, the catalytic reactivities of group 10 metal hydride complexes supported by a PNCNP pincer ligand, [2,6-(tBu2PNH)2C6H3]MH (M = Ni, 1a; Pd, 1b; Pt, 1c), against the hydroboration of CO2 with NH3·BH3 and NaBH4 have been explored. Both 1a and 1b readily react with CO2 at room temperature to form the corresponding formato complexes, [2,6-(tBu2PNH)2C6H3]MOC(O)H (M = Ni, 2a; Pd, 2b), in nearly quantitative yields. Treatment of NH3·BH3 with CO2 (1 atm) in 1,4-dioxane or THF at room temperature in the presence of 0.05-1.0 mol % of 1b followed by hydrolysis of the resulting mixtures produces formic acid in 105-186% yields, and initial turnover frequencies of up to 2000 h-1 are observed. In the presence of 1.0 mol % of 1b, NaBH4 reacts with CO2 (1 atm) in THF at room temperature to form NaB[OC(O)H]4 (3) in 87% isolated yield. In situ NMR spectroscopy indicates that the reactions proceed through the insertion of the C═O bond in CO2 into the Pd-H bond in 1b to form 2b, which sequentially reacts with the hydrides in NH3·BH3 or NaBH4 to produce boron formato species and regenerate 1b. This work represents one of the rare examples of catalytic transfer hydrogenation of CO2 with NH3·BH3 to the formic acid level under very mild conditions without any additives and also the first example of 4 equiv of CO2 uptake by NaBH4 in a reaction.

Ruthenium Complexes of a Triphosphorus-Coordinating Pincer Ligand: Ru–P Ligand-Substituent Exchange Reactions Driven by Large Variations of Bond Energies

The reaction of [(p-cymene)RuCl2]2 with the triphosphine ligand bis(2-di-tert-butylphosphinophenyl)phosphine (tBuPHPP) results in an unusual exchange reaction in which a chloride ligand and a phosphorus-bound H atom are exchanged ("H-P/Ru-Cl exchange") to give the (chlorophosphine)ruthenium hydride complex (tBuPClPP)RuHCl [1Cl-HCl; tBuPClPP = bis(2-di-tert-butylphosphinophenyl)chlorophosphine]. Density functional theory calculations indicate that the presumed initial product of metalation, (tBuPHPP)RuCl2 (1H-Cl2), undergoes an H-P/Ru-Cl exchange via sequential P-to-Ru α-H migration to give the intermediate (tBuPPP)RuHCl2, followed by Ru-to-P α-Cl migration to give the observed product 1Cl-HCl (crystallographically characterized). Dehydrochlorination of 1Cl-HCl under a H2 atmosphere gives (tBuPClPP)RuH4 (1Cl-H4), which then can undergo a second dehydrochlorination and addition of H2 to give (tBuPHPP)RuH4 (1H-H4). This reaction may proceed via the reverse of the intramolecular exchange by 1H-Cl2, i.e., loss of H2 from 1Cl-H4 to give 1Cl-H2, which could undergo Cl-P/Ru-H exchange to give (tBuPHPP)RuHCl (1H-HCl). Accordingly, the thermodynamics of Cl-P/Ru-H exchange are found to be highly dependent on the nature of the ancillary anionic ligand (H or Cl), which is not directly involved in the exchange. The origin of this thermodynamic dependence can be explained in terms of the high stability of complexes (RPXPP)RuHCl (X = H, Cl; R = Me, tBu), in which the hydride is approximately trans to a vacant coordination site and the central phosphine group is approximately trans to the weak-trans-influence chloride ligand. This conclusion has general implications for five-coordinate d6 complexes, both pincer- and nonpincer-ligated.

Catalytic Properties of Zirconocene-Based Systems in 1-Hexene Oligomerization and Structure of Metal Hydride Reaction Centers

Despite large-scale investigations of homogeneous single-site metallocene catalysts and systems based on them, there are still unsolved problems related to the control of their activity and chemo- and stereoselectivity. A solution to these problems is required to develop efficient methods for the synthesis of practically useful products of alkene transformations, such as dimers, oligomers, and polymers. Here we studied the catalytic activity of structurally diverse zirconocenes (L2ZrCl2, L = Cp, C5Me5, Ind, L2 = Me2CCp2, Me2SiCp2, Me2C2Cp2, rac-Me2CInd2, rac-H4C2Ind2, BIPh(Ind)2, H4C2[THInd]2), and co-catalysts activating the system, namely HAlBui2, MMAO-12, and (Ph3C)[B(C6F5)4], at low activator/Zr ratios in a 1-hexene oligomerization reaction. The influence of catalyst structure and system composition on the alkene conversion, the type of products, and the reaction stereoselectivity were investigated. The composition of hydride intermediates formed in the L2ZrCl2-HAlBui2-activator system (L2 = ansa-Me2CCp2, Ind) was studied by NMR spectroscopy. Participation of the bis-zirconium hydride complex as the precursor of catalytically active sites of the alkene dimerization reaction was shown.

Dual Routes toward Observation of a trans-H2/Hydride Complex in an Iridium Pincer System and Hydrogenation Catalytic Activity

ion of chloride from a six-coordinate complex, trans-[Ir(H)(Cl)(iPr)4(POCOP)(PPh3)] (1) [(iPr)4(POCOP) = 2,6-bis(di-iso-propylphosphinito)benzene, κ3-C6H3-1,3-[OP(iPr)2]2], using NaBAr4f leads to the generation of a dinitrogen complex, trans-[Ir(H)(N2)(iPr)4(POCOP)(PPh3)][BAr4f] (6). Addition of H2 to [Ir(H)(N2)(iPr)4(POCOP)(PPh3)]+ (6) under extremely mild conditions (1 bar, 298 K) resulted in the reversible coordination of H2 to generate the cis-[Ir(H)(η2-H2)(iPr)4(POCOP)(PPh3)]+ (cis-11) complex. The cis-[Ir(H)(η2-H2)(iPr)4(POCOP)(PPh3)]+ complex (cis-11) isomerized to a trans isomer, trans-[Ir(H)(η2-H2)(iPr)4(POCOP)(PPh3)]+ (trans-11), at 253 K. The isomerization process has been studied and supported by computations. Employing an alternative route, protonation of the trans-[Ir(H)2(iPr)4(POCOP)(PPh3)] complex (2) at 183 K resulted in the formation of an identical, trans-[Ir(H)(η2-H2)(iPr)4(POCOP)(PPh3)]+ complex (trans-11); upon warming the sample, the trans-H2/hydride complex isomerized to the cis isomer above 253 K. Two independent routes to obtain trans-[Ir(H)(η2-H2)(iPr)4(POCOP)(PPh3)]+ (trans-11) species have been established. Reaction of trans-[Ir(H)(N2)(iPr)4(POCOP)(PPh3)][BAr4f] (6) with C2H4 gave the cis-[Ir(H)(η2-C2H4)(iPr)4(POCOP)(PPh3)]+ complex (cis-15), which also undergoes isomerization to yield an equilibrium mixture of cis/trans-[Ir(H)(η2-C2H4)(iPr)4(POCOP)(PPh3)]+ complexes (cis-15 and trans-15) at 253 K. The trans-[Ir(H)(N2)(iPr)4(POCOP)(PPh3)]+ complex (6) is an excellent catalyst for hydrogenation of ethylene to ethane under very mild conditions.

Dehydrogenation and low-pressure hydrogenation properties of NaAlH4 confined in mesoporous carbon black for hydrogen storage

For hydrogen to be successfully used as an energy carrier in a new renewable energy driven economy, more efficient hydrogen storage technologies have to be found. Solid-state hydrogen storage in complex metal hydrides, such as sodium alanate (NaAlH4), is a well-researched candidate for this application. A series of NaAlH4/mesoporous carbon black composites, with high NaAlH4 content (50–90 wt%), prepared via ball milling have demonstrated significantly lower dehydrogenation temperatures with intense dehydrogenation starting at ∼373 K compared to bulk alanate's ≥ 456 K. Dehydrogenation/hydrogenation cycling experiments have demonstrated partial hydrogenation at 6 MPa H2 and 423 K. The cycling experiments combined with temperature-programmed dehydrogenation and powder X-ray diffraction have given insight into the fundamental processes driving the H2 release and uptake in the NaAlH4/carbon composites. It is established that most of the hydrogenation behavior can be attributed to the Na3AlH6 ↔ NaH transition.

Reactions of PNCNP and POCOP Pincer Platinum Hydride Complexes with Phenylacetylene and Carbon Disulfide: The Influence of the Pincer Backbone on the Structures of Unsaturated Auxiliary Ligands

In order to get information about the influence of the pincer backbone on the structure and reactivity of a pincer complex, bisphosphiamine PNCNP and bisphosphinite POCOP pincer platinum hydride complexes, [2,6-(tBu2PY)2C6H3]PtH (Y = NH, 1a; O, 2a), were reacted with phenylacetylene and carbon disulfide. The reactions with phenylacetylene in the presence of CuI/Et2NH produced the corresponding σ-alkynyl complexes [2,6-(tBu2PY)2C6H3]PtC≡CPh (Y = NH, 1b; O, 2b). The reactions with carbon disulfide produced the corresponding dithioformato complexes [2,6-(tBu2PY)2C6H3]PtSC(S)H (Y = NH, 1c; O, 2c). The PNCNP complex 1a is easier to react with carbon disulfide than the POCOP complex 2a. X-ray crystal structure analysis indicated that the PNCNP pincer backbone influences the phenylacetylido and dithioformato auxiliary ligands in the resulting complexes more significantly than the POCOP pincer backbone. The dithioformato auxiliary ligand adopts different coordination modes in complexes 1c and 2c. The results provide useful information about how PNCNP and POCOP pincer backbones influence the reactivity of the metal center and the coordination of unsaturated auxiliary ligands.

Oxo‐Bridged Zr Dimers as Well‐defined Models of Oxygen Vacancies on ZrO2

AbstractWhile ZrO2 is known to have a large effect on the activity and selectivity of the Cu/ZrO2 catalyst for methanol synthesis, its role in this process is poorly understood. Surface defects such as oxygen vacancies could play a role in the strong metal‐support interaction (SMSI) between Cu and ZrO2. However, due to the complexity of the surfaces, the exact molecular nature of this interaction is not at present known. Here, we make well‐defined models of both reduced and coordinatively unsaturated surface oxygen vacancies on ZrO2 using the molecular precursor [Cp2ZrCl]2(μ2‐O) (1). Complex 1 can be reduced to form a complex (2) containing one Zr(III) center and a bridging hydride ligand (according to EPR and IR spectroscopy) derived from C−H activation of either thf or the Cp ring. Complex 2 reacts with CO2 to largely produce CO, suggesting that surface defects with similar structures probably do not play a role in the industrial catalyst. Halide abstraction from complex 1 results in the Lewis acidic species 3, which has similar Lewis acid properties to acidic defects on the ZrO2 surface. Similarities of both of these model species to real surface oxygen vacancies and their role in the catalytic reaction are discussed.

Exploring Rhenium Arene Piano-Stool Chemistry with [Re(η6-C6H6)(NCCH3)3]+: A Powerful Semi-Solvated Precursor.

Thermal treatment of the ReIII hydride complex [ReH(η5-C6H7)(η6-C6H6)]+ in CH3CN results in the formation of [Re(η6-C6H6)(NCCH3)3]+. This semi-solvated complex is remarkably stable under an ambient atmosphere and exhibits a fast CH3CN self-exchange, which facilitates substitution reactions. The CH3CN ligands are replaced by σ-donating phosphines such as trimethyl phosphine (PMe3), triphenyl phosphine (PPh3), or the bidentate 1,2-bis(diphenylphosphino)ethane (dppe) to afford [Re(η6-C6H6)(NCCH3)3-x(PR3)x]+ (if R = Me, then x = 2; if R = Ph, then x = 1 or 2) or [Re(η6-C6H6)(dppe)(NCCH3)]+, respectively. [Re(η6-C6H6)(NCCH3)3]+ also reacts with π-acceptors such as 2,2'-bipyridine (bipy), 1,10-phenanthroline (phen), or CO (1 atm) to give [Re(η6-C6H6)(L)(NCCH3)]+ (L = bipy or phen) and [Re(η6-C6H6)(CO)(NCCH3)2]+, respectively. The latter does not show any signs of decomposition after being exposed to an ambient atmosphere for multiple days. Additionally, [Re(η6-C6H6)(NCCH3)3]+ reacts with π-donors such as the dienes 2,3-dimethyl-1,3-butadiene (DMBD), norbornadiene (NBD), or 1,5-cyclooctadiene (COD) to give [Re(η6-C6H6)(η4-diene)(NCCH3)]+ (diene = DMBD, NBD, and COD). All three complexes are extremely stable and do not decompose during purification by preparative high-performance liquid chromatography (aqueous acidic gradient). In the presence of 18-crown-6, [Re(η6-C6H6)(NCCH3)3]+ reacts with lithium cyclopentadienyl to give the sandwich complex [Re(η5-C5H5)(η6-C6H6)]. Loss of the coordinated benzene was observed when treating [Re(η6-C6H6)(NCCH3)3]+ with diphenylacetylene (PhC≡CPh), yielding the tetra-coordinated [Re(NCCH3)(η2-PhC≡CPh)3]+.

Undirected C-H Bond Activation in Aluminium Hydrido Enaminonates.

Two new aluminium hydrido complexes were synthesized by reacting AlH3 with the enaminone ligand N-(4,4,4-trifluorobut-1-en-3-on)-6,6,6-trifluoroethylamine (HTFB-TFEA) in different molar ratios to obtain mono- and di-hydrido-aluminium enaminonates. Both air and moisture sensitive compounds could be purified via sublimation under reduced pressure. The spectroscopic analysis and structural motif of the monohydrido compound [H-Al(TFB-TBA)2] (3) showed a monomeric 5-coordinated Al(III) centre bearing two chelating enaminone units and a terminal hydride ligand. However, the dihydrido compound exhibited a rapid C-H bond activation and C-C bond formation in the resulting compound [(Al-TFB-TBA)-HCH2] (4a), which was confirmed by single crystal structural data. The intramolecular hydride shift involving the migration of a hydride ligand from aluminium centre to the alkenyl carbon of the enaminone ligand was probed and verified by multi-nuclear spectral studies (1H,1H NOESY, 13C, 19F, and 27Al NMR).

Trans Ligand Determines the Stability of Paramagnetic Manganese(II) Hydrides of the Type trans-[MnH(L)(dmpe)2]+ Where L is PMe3, C2H4, or CO.

Paramagnetic metal hydride (PMH) complexes play important roles in catalytic applications and bioinorganic chemistry. 3d PMH chemistry has largely focused on Ti, Mn, Fe, and Co. Various MnII PMHs have been proposed as intermediates in catalysis, but isolated MnII PMHs are limited to dimeric high-spin MnII structures with bridging hydrides. In this paper, a series of the first low-spin monomeric MnII PMH complexes are generated by chemical oxidation of their MnI analogues. This series is of the type trans-[MnH(L)(dmpe)2]+/0 where the trans ligand L is PMe3, C2H4, or CO [dmpe is 1,2-bis(dimethylphosphino)ethane], and the thermal stability of the MnII hydride complexes was found to be strongly dependent on the identity of the trans ligand. When L is PMe3, the complex is the first example of an isolated monomeric MnII hydride complex. In contrast, when L is C2H4 or CO, the complexes are only stable at low temperatures; upon warming to room temperature, the former decomposed to afford [Mn(dmpe)3]+, accompanied by ethane and ethylene, whereas the latter eliminated H2, generating [Mn(MeCN)(CO)(dmpe)2]+ or a mixture of products including [Mn(κ1-PF6)(CO)(dmpe)2], depending on the reaction conditions. All PMHs were characterized by low-temperature electron paramagnetic resonance (EPR) spectroscopy, and stable [MnH(PMe3)(dmpe)2]+ was further characterized by UV-vis and IR spectroscopy, Superconducting Quantum Interference Device magnetometry, and single-crystal X-ray diffraction. Noteworthy spectral properties are the significant EPR superhyperfine coupling to the hydride (∼85 MHz) and an increase (+33 cm-1) in the Mn-H IR stretch upon oxidation. Density functional theory calculations were also employed to gain insights into the acidity and bond strengths of the complexes. MnII-H bond dissociation free energies are estimated to decrease in the series of complexes from 60 (L = PMe3) to 47 kcal/mol (L = CO).

Improving the Cycle Life of Solid-State Batteries by Addition of Oxide Nanoparticles to a Complex Hydride Solid Electrolyte

We report that the addition of silica nanoparticles to the iodide-substituted LiBH4 (h-Li(BH4)0.8(I)0.2) improves the ion conductivity and, remarkably, the cycle life of the all-solid state batteries. The h-Li(BH4)0.8(I)0.2-SiO2 was synthesized by mechanochemical treatment and possesses a Li+ conductivity of 9.3 × 10–5 S cm–1 at RT. It has an electrochemical stability window of about 2.5 V vs Li+/Li and an improved stability against Li-metal, compared to h-Li(BH4)0.8(I)0.2, owing to the addition of oxide nanoparticles, which we ascribed to a greater mechanical stability of the solid-state electrolyte. The all-solid state battery Li|h-Li(BH4)0.8(I)0.2-SiO2|TiS2 demonstrated a good long-term cyclability, i.e., over 200 cycles at C/20 and even including a C-rate of C/5, demonstrating that the addition of oxide nanoparticles improves the cycling stability of the electrolyte.

Structural phase stability and thermodynamical properties of transition metal complex hydrides Na2MgTMH7 (TM=Sc−Cu) for hydrogen storage applications

In order to predict ground state structure as well as thermodynamical properties of transition metal-based complex hydrides (TMCHs) and identify potential hydrogen storage materials for energy storage applications, we have performed first-principles density functional spin polarized total energy calculations for Na2MgTMH7 where TM ​= ​Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. To investigate the thermodynamical properties of transition metal-based complex hydrides (TMCHs) and to find potential hydrogen storage materials for energy storage applications. Our spin-polarized calculations show that all these materials are having a finite magnetic moment at the transition metal site with ferromagnetic or anti−ferromagnetic ordering as ground state configuration except the cases where TM ​= ​Sc, Co, Ni, and Cu. Our calculated enthalpy of formation and hydrogen site energy of TMCHs suggest that these systems are stable and the hydrogen is expected to release at a relatively low temperature compared to that of pure binary hydrides. We have performed the chemical bonding analyses between the constituents of TMCHs through density of states, charge density, electron localization function, Born effective charge, Bader effective charge, Mulliken charge, and COHP and these analyses suggest that there is an ionic bonding between hydrogen with Na, Mg, and transition metal with noticeable covalent bonding between hydrogen and Mg/TM.

A Terminal Hydride of Hafnium Supported by a Triamidoamine Ligand

A mononuclear hafnium hydride supported by an aryl-substituted triamidoamine ligand [HfH(thf)(Xy-N3N)] (Xy-N3N = {(3,5-Me2C6H3)NCH2CH2}3N3–) was synthesized by either hydrogenolysis of the hydrocarbyl complex [Hf(R)(thf)(Xy-N3N)] (R = Me, CH2SiMe3, η3-C3H5, CH2Ph) in tetrahydrofuran (THF) or, more conveniently, by salt metathesis of the chloro precursor [HfCl(thf)(Xy-N3N)] with NaBEt3H in methylcyclohexane. The structure of a terminal hydride with a distorted capped trigonal bipyramidal geometry was characterized by single crystal X-ray diffraction (d(Hf–H): 1.83(3) Å) and by 1H NMR spectroscopy. The unusually low field shifted 1H chemical shift for the hydride ligand was detected at δ 18.28 ppm. Dehydrogenative thermolysis of the hydride complex at 25 °C in benzene or toluene resulted in deprotonation of the α-hydrogen of one of the three XyNCH2CH2 groups in the ligand by the hydride, followed by the combination of this deprotonated anionic complex with cationic complex [Hf(Xy-N3N)]+ to give an unsymmetric dinuclear complex bridged by μ-H, μ-NXy, and μ,κN,κC-XyNCHCH2 groups. This decomposition product was characterized by single crystal X-ray diffraction and by 1H and 13C NMR spectroscopy and analyzed by density functional theory (DFT) calculations. Hydrogenation in THF at 25 °C reformed the hydride complex over a period of 48 h. The hydride complex reacted with olefins RHC═CH2 (R = H, Et, nHex, cHex, Ph) to give the corresponding anti-Markovnikov insertion products [Hf(CH2CH2R)(thf)n(Xy-N3N)]. Catalytic hydrogenation of olefins was achieved with 5 mol % of the hydride complex at 70 °C in THF or benzene.

Poly-Hydride [AuI 7 (PPh3 )7 H5 ](SbF6 )2 cluster complex: Structure, Transformation, and Electrocatalytic CO2 Reduction Properties.

Hydride AuI bonds are labile due to the mismatch in electric potential of an oxidizing metal and reducing ligand, and therefore the structure and structure-activity relationships of nanoclusters that contain them are seldom studied. Herein, we report the synthesis and characterization of [Au7 (PPh3 )7 H5 ](SbF6 )2 (abbrev. Au7 H5 2+ ), an Au cluster complex containing five hydride ligands, which decomposed to give [Au8 (PPh3 )7 ]2+ (abbrev. Au8 2+ ) upon exposure to light (300 to 450 nm). The valence state of AuI and H- was verified by density functional theory (DFT) calculations, NMR, UV/Vis and XPS. The two nanoclusters behaved differently in the electrocatalytic CO2 reduction reaction (CO2 RR): Au7 H5 2+ exhibited 98.2 % selectivity for H2 , whereas Au8 2+ was selective for CO (73.5 %). Further DFT calculations showed that the H- ligand inhibited the CO2 RR process compared with the electron-donor H.