Mixed Borohydride Research Articles

Investigation on the Decomposition Enthalpy of Novel Mixed Mg(1–x)Znx(BH4)2 Borohydrides by Means of Periodic DFT Calculations

The combination of Mg(BH4)2 and Zn(BH4)2 compounds has been theoretically investigated as a possible mixed borohydride prone to give an enthalpy of decomposition around 30 kJ/molH2, that is, suitable for a dehydrogenation process close to room temperature and pressure. The total energy of pure compounds and solid solutions has been computed by means of periodic DFT calculations. To generate the Mg(1–x)Znx(BH4)2 solid solutions, the α-phase of Mg(BH4)2 (space group P6122) has been considered in which Mg2+ ions have been progressively replaced with Zn2+, without lowering the symmetry of the crystalline structure. A charge density topological analysis is reported to better understand the chemical bonding in the pure and mixed metal borohydrides. The decomposition enthalpy of the mixed borohydrides according to two different reaction paths that lead to MgH2, Zn, H2, and α-B or B2H6, respectively, as products has been estimated. As regards the former, a value of about 30 kJ/molH2 has been predicted for a Mg(1–x)Znx(BH4)2 solid solution with x = 0.2–0.3.

Nuclear Magnetic Resonance Study of Atomic Motion in the Mixed Borohydride–Amide Na2(BH4)(NH2)

To study the reorientational motion of the anions and the translational diffusion of Na+ cations in the mixed borohydride–amide Na2(BH4)(NH2) showing fast-ion conduction, we have measured the 1H, 11B, and 23Na NMR spectra and spin–lattice relaxation rates in this compound over broad ranges of temperature (6–480 K) and the resonance frequency (14–132.3 MHz). At low temperatures (T < 190 K), the proton spin–lattice relaxation rate is governed by fast reorientations of BH4 groups. This reorientational process can be satisfactorily described in terms of a Gaussian distribution of the activation energies with the average Ea value of 74 ± 7 meV. Above 250 K, the measured proton spin–lattice relaxation rate originates from two other (slower) reorientational jump processes characterized by the average activation energies of 340 ± 9 meV and 559 ± 7 meV. The 23Na spin–lattice relaxation data in the high-temperature region are governed by translational diffusion of Na+ ions, which is consistent with high Na-ion cond...

Breaking the passivation—the road to a solvent free borohydride synthesis

We describe a new method for the solvent-free synthesis of borohydrides at room temperature and demonstrate its feasibility by the synthesis of three of the most discussed borohydrides at present: LiBH(4), Mg(BH(4))(2) and Ca(BH(4))(2). This new gas-solid mechanochemical synthesis method is based on the reaction of metal hydrides with diborane to form the corresponding borohydrides. The synthesis will facilitate the preparation of a wide range of different borohydrides, including mixed borohydride systems, with tuneable sorption properties. We propose that diborane is an intermediate compound for the hydrogen sorption in borohydrides and may be the key for a reversible hydrogen ab- and desorption reaction under moderate conditions.

Preparation and Crystal Structure of the Neodymium Borohydride [Li(thf)4]2[Nd2(μ‐Cl)2(BH4)6(thf)2

AbstractThe neodymium borohydride [Li(thf)4]2[Nd2(μ‐Cl)2(BH4)6(thf)2] was synthesized from neodymium chloride and lithium borohydride. The compound crystallized in the triclinic crystal system, space group $P{\bar 1}$ (No. 2) with the cell constants a = 14.8613(11), b = 17.8715(13), c = 23.5846(18) Å, α = 100.760(6), β = 90.648(6) and γ = 103.294(6)°. Each neodymium atom is coordinated by three borohydride anions and a THF molecule whereas two neodymium cations are bridged through two chloro ligands. The charge of the [Nd2(μ‐Cl)2(BH4)6(thf)2]2− anion, which represents the first structurally characterized binuclear mixed borohydride chlorido complex, is compensated by two [Li(thf)4]+ cations.

Encapsulation of hydride by molecular main group metal clusters: manipulating the source and coordination sphere of the interstitial ion

The sequential treatment of Lewis acids with N,N'-bidentate ligands and thereafter with ButLi has afforded a series of hydride-encapsulating alkali metal polyhedra. While the use of Me3Al in conjunction with Ph(2-C5H4N)NH gives Ph(2-C5H4N)NAlMe2 and this reacts with MeLi in thf to yield the simple 'ate complex Ph(2-C5H4N)NAlMe3Li.thf, the employment of an organolithium substrate capable of beta-hydride elimination redirects the reaction significantly. Whereas the use of ButLi has previously yielded a main group interstitial hydride in which H- exhibits micro6-coordination, it is shown here that variability in the coordination sphere of the encapsulated hydride may be induced by manipulation of the organic ligand. Reaction of (c-C6H11)(2-C5H4N)NH with Me3Al/ButLi yields [{(c-C6H11)(2-C5H4N)N}6HLi8]+[(But2AlMe2)2Li]-, which is best viewed as incorporating only linear di-coordination of the hydride ion. The guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) in conjunction with Me2Zn/ButLi yields the micro8-hydride [(hpp)6HLi8]+[But3Zn]-.0.5PhMe. Formation of the micro8-hydride [(hpp)6HLi8]+[ButBEt3]- is revealed by employment of the system Et3B/ButLi. A new and potentially versatile route to interstitial hydrides of this class is revealed by synthesis of the mixed borohydride-lithium hydride species [(hpp)6HLi8]+[Et3BH]- and [(hpp)6HLi8]+[(Et3B)2H]- through the direct combination of hppLi with Et3BHLi.

NaBH 4 in N-methylpyrrolidone: a safe alternative for hydride displacement reaction

Enhanced reactivity of NaBH 4 was observed as a solution in N-methylpyrrolidone (NMP). Thus, a simple protocol for debromination of alkyl bromide and sulfonate is devised with NMP as a key solvent. Also described is a new mixed borohydride system, NaBH 4–LiOTf–NMP, which works as an alternative to NaBH 3CN for the S N2 type displacement. No reports have ever revealed usefulness of NMP in borohydride reduction.

An efficient conversion of 5-nitroisatin into 5-nitroindole derivative

Our process research on OPC-35564 revealed that a mixed borohydride reducing agent (ZrCl 4/NaBH 4) in DME (Itsuno system) afforded a rapid and direct conversion of N-alkyl-nitroisatin into nitroindole nucleus. Comparison with other reducing agents indicated the superiority of the present system and the key function of ZrCl 4. For the manipulation of base-labile isatin, a useful procedure for its N-alkylation using Cu 2CO 3 is also presented.