Manganese Hydride Research Articles

Manganese-Based Molecular Electrocatalysts for Oxidation of Hydrogen

Oxidation of H2 (1 atm) is catalyzed by the manganese electrocatalysts [(P2N2)MnI(CO)(bppm)]+ and [(PNP)MnI(CO)(bppm)]+ (P2N2 = 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; PNP = (Ph2PCH2)2NMe); bppm = (PArF2)2CH2; ArF = 3,5-(CF3)2C6H3). In fluorobenzene solvent using 2,6-lutidine as the exogeneous base, the turnover frequency for [(P2N2)MnI(CO)(bppm)]+ is 3.5 s–1, with an estimated overpotential of 700 mV. For [(PNP)MnI(CO)(bppm)]+ in fluorobenzene solvent using N-methylpyrrolidine as the exogeneous base, the turnover frequency is 1.4 s–1, with an estimated overpotential of 880 mV. Density functional theory calculations suggest that the slow step in the catalytic cycle is proton transfer from the oxidized 17-electron manganese hydride [(P2N2)MnIIH(CO)(bppm)]+ to the pendant amine. The computed activation barrier for intramolecular proton transfer from the metal to the pendant amine is 20.4 kcal/mol for [(P2N2)MnIIH(CO)(bppm)]+ and 21.3 kcal/mol for [(PNP)MnIIH(CO)(bppm)]+. The high barrier appears to result from both the unfavorability of the metal to nitrogen proton transfer (thermodynamically uphill by 9 kcal/mol for [(P2N2)MnIIH(CO)(bppm)]+ due to a mismatch of 6.6 pKa units) and the relatively long manganese–nitrogen separation in the MnIIH complexes.

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of NH Imines and Alkynes by CH/NH Activation

AbstractDescribed herein is a manganese‐catalyzed dehydrogenative [4+2] annulation of NH imines and alkynes, a reaction providing highly atom‐economical access to diverse isoquinolines. This transformation represents the first example of manganese‐catalyzed CH activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H2 as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition‐metal‐catalyzed CH activation. Mechanistic studies revealed the five‐membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of NH Imines and Alkynes by CH/NH Activation

Described herein is a manganese-catalyzed dehydrogenative [4+2] annulation of NH imines and alkynes, a reaction providing highly atom-economical access to diverse isoquinolines. This transformation represents the first example of manganese-catalyzed CH activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H2 as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition-metal-catalyzed CH activation. Mechanistic studies revealed the five-membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.

An Efficient Catalyst Based on Manganese Salen for Hydrosilylation of Carbonyl Compounds

A manganese salen complex is shown to be an effective (pre)catalyst in the hydrosilylation of aldehydes and ketones. The present system features an earth-abundant and inexpensive base metal, low catalyst loading, and functional group tolerance. Mechanistic studies suggest that the reaction likely proceeds through a reduced manganese(III) hydride species that undergoes electrophilic attack by the carbonyl substrates.

Rapid, Reversible Heterolytic Cleavage of Bound H2

Heterolytic cleavage of dihydrogen into a proton and a hydride ion is a fundamentally important step in many reactions, including the oxidation of hydrogen by hydrogenase enzymes and ionic hydrogenation of organic compounds. We report the facile, reversible heterolytic cleavage of H2 in a manganese complex bearing a pendant amine, leading to the formation of a manganese hydride and a protonated amine that undergo H(+)/H(-) exchange at an estimated rate of >10(7) s(-1) at 25 °C.

Facile Metalation of Silicon and Germanium Analogues of Thiocarboxylic Acids with a Manganese(II) Hydride Precursor

Synthesis and characterization of the first manganese(II)-containing heavier thiocarboxylate analogues, [L(Dip)Si(=S)OMnL(Dep)] (4; L(Dip)=CH[C(Me)N(2,6-iPr(2)C(6)H(3))](2), L(Dep)=CH[C(Me)N(2,6-Et(2)C(6)H(3))](2)) and [L(Dip)Ge(=S)OMnL(Dep)] (5) are described. They are accessible through reaction of the silicon and germanium analogues of the respective thiocarboxylic acids [L(Dip)E(=S)OH] (E=Si, Ge) with the β-diketiminato (nacnac) manganese(II) hydride precursor [(L(Dep)Mn)(2)(μ-H)(2)] (3) in high yield. The first Mn nacnac hydride 3 has been prepared by the reaction of manganese bromide [(L(Dep)Mn)(2)(μ-Br)(2)] (2) with KBEt(3)H. Compounds 4 and 5 represent the first transition-metal heavier thiocarboxylates with the Si=S and Ge=S functionalities. All new compounds are paramagnetic and were characterized by elemental analysis, IR spectroscopy, MS (EI), and single-crystal X-ray diffraction analyses. Due to the N→E (E=Si, Ge) and E=S→Mn donor-acceptor interaction as well as the carboxylate-like π-electron delocalization within the E(S)O moieties, the E=S double bonds in these compounds are resonance stabilized.

Theoretical study of manganese hydrides and halides, MnXn with X = H, F, Cl, Br and n = 1–4

Properties of a series of MnXn with X=H, F, Cl, Br and n=1–4 are investigated using DFT, CCSD(T) and CASPT2 computations. The B3P86/6-311++G(3df,2d) method appears to be suitable for predicting their structures whose geometries and IR spectra are dependent on the charge state. While MnX2 are linear, MnX3 and MnX4 are characterized by high symmetry shape. The π-bonding type is observed for MnH30/+ and MnH40/+. In halides, a different type of bonds is formed as p-orbitals of halogens can overlap with empty metal d-orbitals allowing a more effective electron transfer and high spin ground electronic states. Vibrational frequencies and basic energetic quantities are computed and compared with available experiments. Several previous thermochemical quantities are re-evaluated, and the heats of formation of Mn-compounds can be determined with reasonable accuracy using the B3LYP functional. However, while calculated ionization energies are in agreement with experiment, electron affinities are obtained with large deviations.

Nuclear quadrupole interaction studies ofC15RMn2hydrides (R=Y,Gd,Tb,Dy)

The nuclear electric quadrupole interaction (QI) of the probe nucleus $^{111}\text{I}\text{n}/^{111}\text{C}\text{d}$ in the paramagnetic phase of the $C15$ rare earth $(R)$--manganese hydrides (deuterides) $R{\text{Mn}}_{2}\text{H}{(D)}_{x}$, with $R=\text{Y}$, Gd, Tb, and Dy, has been investigated by perturbed angular-correlation spectroscopy. The QI between the $^{111}\text{C}\text{d}$ quadrupole moment and the electric-field gradient (EFG) at the probe nucleus on the Mn site has been measured as a function of temperature in ${\text{TbMn}}_{2}\text{H}{(D)}_{x}$ in the concentration range $0\ensuremath{\le}x\ensuremath{\le}4.3$ and in $R{\text{Mn}}_{2}\text{H}{(D)}_{x}$, $R=\text{Y}$,Gd,Dy at the highest H content of $x\ensuremath{\sim}4.3$. The relative temperature dependence of the EFG in the parent compounds $R{\text{Mn}}_{2}$ is twice as strong as in isostructural $R{\text{Al}}_{2}$ which can be related to differences in the Debye temperatures resulting from different radius ratios ${r}_{R}/{r}_{\text{Mn}}$ and ${r}_{R}/{r}_{\text{Al}}$ [Joseph-Gschneidner postulate, Scr. Metall.2, 631 (1968)]. Hydrogenation of $R{\text{Mn}}_{2}$ increases the magnitude of the EFG by a factor of 2 between $x=0$ and $x=4.3$ but leaves the relative temperature dependence almost unchanged. Only at concentrations $x>3.6$ the temperature coefficient of the QI is significantly larger than in uncharged $R{\text{Mn}}_{2}$. These results are compared with the much stronger concentration dependence and the anomalous temperature dependence of the QI of $^{111}\text{C}\text{d}$ in the $C15$ hydrides ${\text{HfV}}_{2}{\text{H}}_{x}$. Evidence for an exceptionally high H mobility in ${\text{TbMn}}_{2}{\text{H}}_{x}$ is presented. The measurements provide information on structural changes and magnetic ordering temperatures at different H concentrations.

Analysis of hydrogen adsorption in the bulk and on the surface of magnesium nanoparticles

The stability of magnesium hydride (MgH x ) nanoparticles (x = 0.5, …, 2) is investigated using ab initio calculations. It is shown that for a nanoparticle diameter of D ∼ 5 nm, the internal pressure becomes lower than 3 kbar; for this reason, the structure of hydride nanoparticles coincides with the structure of this hydride in crystalline form. It is found that the phase of partly saturated MgH x hydrides (x < 2) must decompose into the phase of pure hcp magnesium and the α phase of MgH2. The frequencies of jumps of hydrogen atoms within the hcp phase of magnesium and in the α phase of MgH2 are calculated; it is shown that slow diffusion of hydrogen in magnesium is due to the large height of potential barriers for motion of hydrogen within MgH2. To attain high diffusion rates, the structures of Mg53Sc and Mg53Ti crystals and their hydrides are calculated. It is found that the frequency of jumps of H atoms in Mg53ScH108 near the Sc atoms does not noticeably change as compared to the frequency of jumps in the α phase of MgH2, while the frequency of jumps in Mg53TiH108 near Ti atoms is higher by approximately a factor of 2.5 × 106. This means that diffusion in manganese hydride with small admixtures of titanium atoms must be considerably eased. Chemical dissociation of hydrogen molecules on the (0001) surface of hcp magnesium, on the given surface with adjoined individual Ti atoms, and on the surface of a one-layer titanium cluster on the given surface of magnesium is investigated. It is found that dissociation of hydrogen at solitary titanium atoms, as well as on the surface of a Ti cluster, is facilitated to a considerable extent as compared to pure magnesium. This should also sharply increase the hydrogen adsorption rate in magnesium nanoparticles.

Matrix Infrared Spectra and Density Functional Theory Calculations of Manganese and Rhenium Hydrides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Matrix Infrared Spectra and Density Functional Theory Calculations of Manganese and Rhenium Hydrides

Laser-ablated Mn and Re atoms react with H2 upon co-condensation in excess argon and neon and in pure hydrogen to produce metal hydrides. The reaction products are identified through isotopic substitution (D2, HD, and H2 + D2) and density functional theory calculations. The 7Σ+ ground state diatomic MnH is observed at 1493.3 cm-1 in solid neon, 1486.4 cm-1 in hydrogen, and 1477.9 cm-1 in argon. The ReH molecule gives a sharp band at 1985.0 cm-1 in argon, which is suggested to be the 5Σ+ ground state by DFT calculations. The MnH2 molecule provides ν3 modes at 1600.8 cm-1 in solid neon, 1598.0 cm-1 in solid hydrogen, and 1592.3 cm-1 in solid argon, and the analogous ReH2 molecule absorbs at 1646.4 cm-1 in solid argon. In addition MnH2- is observed at 1465.6 cm-1 in solid neon. The bonding properties of the first row transition metal dihydrides are compared, and reaction mechanisms of Mn and Re with H2 are discussed. The novel ReH4 molecule absorbs at 2037.2 and 590.6 cm-1. This work reports the first experimental evidence for neutral rhenium hydride molecules.

Ab Initio Study of Structure and Spectra of MnH2, MnH2-, and MnH3

Molecules of manganese hydrides MnH 2 , MnH 2 -, and MnH 3 were studied using large basis sets up to spdfg quality and the coupled cluster technique for the treatment of electron correlation. Both MnH 2 and MnH 2 - have linear equilibrium structures in their high spin ground electronic state, the MnH 2 - molecule having a rather flat bending potential. The MnH 3 molecule is Y-shaped with valence angle α(H-Mn-H) = 44.6° in the 5 B 2 ground electronic state due to the strong Jahn-Teller distortion of the trigonal planar structure. The harmonic vibrational frequencies, IR intensities, and the relative energies of excited states were calculated. Fundamental vibrational wavenumbers and electron affinity were also found for MnH 2 . The results are compared with available spectroscopic data.

Electronic structure of the new manganese ternary hydride Mg 3MnH 7

We have investigated the electronic structure of the new manganese hydride Mg 3MnH 7 by calculating ab initio the energy bands, density of states and the partial wave analysis of the density of states at each atomic site. We found that this hydride is an insulator with a large indirect energy gap of 2.56 eV. Partial wave analysis of the density of states shows that the electronic properties of this compound are strongly dominated by the bonding features of the MnH 6 and Mg 2H units.

Diborane(4)yl and bridged borylene complexes from 1,2-dipyrrolidino- and 1,2-dipiperidinodiborane(4) derivatives

Abstract The 1,2-diaminodichlorodiboranes(4) B2(NC4H8)2Cl2 (1) and B2(NC5H10)2Cl2 (2) served as starting materials for the syntheses of the iron diborane(4)yl complexes [Cl(R2N)BB(NR2)Fe(C5H5)(CO)2] (3a, NR2NC4H8; 3b, NR2NC5H10). Upon reaction with the anionic manganese hydride complex K[(C5H4Me)MnH(CO)2], the bridged borylene complexes [{(C5H4Me)Mn(CO)2}2BNR2] (4a, NR2NC4H8; 4b, NR2NC5H10) were obtained with cleavage of the boronboron bond, hydrogen migration from manganese to boron, and formation of the corresponding diboranes(6) (H2BNR2)2. All complexes were obtained as crystalline materials and fully characterized in solution by IR and multinuclear NMR spectroscopy.

Neutron diffraction investigation of γ manganese hydride

A profile analysis of the neutron diffraction spectrum of the fcc high pressure hydride λ-MnH0.41 measured under ambient conditions showed that hydrogen is randomly distributed over the octahedral interstices of the fcc metal lattice and that the hydride is an antiferromagnet with the same collinear spin structure as pure λ-Mn, but with a smaller magnetic moment of about 1.9 Bohr magnetons per Mn atom.

Alkali-metal manganese hydrides: synthesis, structure and magnetic properties

The ternary alkali-metal manganese hydrides A 3MnH 5 and A 3MnD 5 (A = K, Rb, Cs) were synthesised by the reaction of the respective alkali-metal hydride (deuteride) with manganese powder at 875 K under a hydrogen pressure of above 3000 bar. X-ray investigations of the powdered samples and elastic neutron diffraction experiments on the deuterated compounds over the temperature range 2–600 K led to the complete determination of their structures. Their atomic arrangements are isotypic with that of Cs 3[CoCl 4]Cl (space group: I4/mcm, Z=4). The structure contains isolated [MnH 4] 2− tetrahedra with the remaining hydrogen ions exclusively coordinated by the alkali-metal cations. The magnetic susceptibilities show a Curie-Weiss behaviour. Antiferromagnetic interactions were observed at low temperatures. Three different spin structures result from neutron diffraction experiments.

Synthesis and NMR T1 relaxation study of rhenium and manganese hydride complexes

Some new and known hydride complexes of manganese (MnH(NO) 2 (PEt) 2 , MnH(CO) 3 (PEt 3 ) 2 z) and rhenium (ReH(CO) n (PMe 3 ) 5-n =1, 2, 3; ReH 2 (CO)(NO)(PR 3 ) 2 ) were prepared. 1 H selective and nonselective relaxation times were determined as a function of temperature for each compound. From the measurements, the contributions of the M-H dipole-dipole interaction to the relaxation times of the H ligands were solated, and the M-H bond lengths were calculated using the model of an isotropic motion

Gas-phase acidities of pentacarbonyl manganese, iron, and cobalt hydrides, (CO)5MnH, (CO)4FeH2, and (CO)4CoH

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGas-phase acidities of pentacarbonyl manganese, iron, and cobalt hydrides, (CO)5MnH, (CO)4FeH2, and (CO)4CoHAmy E. Stevens Miller and J. L. BeauchampCite this: J. Am. Chem. Soc. 1991, 113, 23, 8765–8770Publication Date (Print):November 1, 1991Publication History Published online1 May 2002Published inissue 1 November 1991https://doi.org/10.1021/ja00023a024RIGHTS & PERMISSIONSArticle Views143Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (838 KB) Get e-Alerts Get e-Alerts

Neutron spectroscopy of MnH 0.86, NiH 1.05, PdH 0.99 and harmonic behaviour of their optical phonons

Inelastic neutron scattering spectra from manganese, nickel and palladium hydrides synthesized under a high pressure of gaseous hydrogen have been measured in the energy region of 0–500 meV. The positions and intensities of the peaks in the higher energy parts of the spectra are well described by a contribution from the multiphonon neutron scattering in the harmonic approximation.

Electronic structure and magnetic ordering in manganese hydride

The self-consistent electron energy bands of antiferromagnetic (AFM) and non-magnetic manganese hydride are calculated using the linear muffintin orbital method (LMTO). The calculated values of equilibrium volume and of magnetic moment on the manganese site are in good agreement with experiment. The Fermi surface of paramagnetic MnH contains two nesting parts, and their superposition gives rise to AFM gap.