Octahydrotriborate Anion Research Articles

New approaches to the synthesis of substituted derivatives of the [B<sub>3</sub>H<sub>8</sub>]<sup>−</sup> anion

Objectives. To develop methods for the synthesis of substituted derivatives of the octahydrotriborate anion. Such compounds can be considered as hydrogen storage, components of ionic liquids, precursors for the production of boride coatings using the traditional chemical vapor deposition method, and also as a building material for the production of higher boron hydrogen clusters.Methods. Since substitution reactions are sensitive to moisture and atmospheric oxygen, the syntheses were carried out in a direct flow of argon or in a dry, sealed SPEKS GB02M glove box with a double gas purification unit and two airlocks. The reaction was initiated by cooling to 0°C, in order to avoid the formation of by-products. All the results were characterized using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies.Results. The study presents a detailed study of the known methods for preparing substituted derivatives of the octahydrotriborate(1−) anion using dry hydrogen chloride as an electrophilic inductor and makes recommendations for improvement. In this method it is advisable to use cesium octahydrotriborate which facilitates the yield of the target product. New methods were proposed to initiate the substitution reaction in the [B3H8]−-anion using N-chlorosuccinimide and bromine. Using these inductors, new substituted derivatives of the octahydrotriborate anion with N-nucleophiles were obtained and defined by means of IR and NMR spectroscopies: [B3H7NCR], (R = Et, i-Pr, Ph) and [B3H7NH2R], (R = C9H19 (INA), Bn), [B3H7NHEt2], as well as Bu4N[B3H7Hal], Bu4N[B3H6Hal2], where Hal = Сl, Br. It was also established that hydrogen bromide is released during the reaction with bromine and amines. This immediately protonates the amine which requires additional heating of the reaction mixture. The study also established that the reaction mechanism with N-chlorosuccinimide is not radical.Conclusions. The main factors influencing the course of the substitution reaction are the possible occurrence of side interactions between the nucleophile and the inducer, steric possibilities, and subsequent isolation of the reactive reaction products.

Ion-Selective Membrane Electrode for Determination of the Octahydrotriborate Anion

An ion-selective electrode (ISE) based on a plasticized polyvinyl chloride membrane chemically doped with tetradecylammonium octahydrotriborate ([(С10H21)4N+]) has been developed. It is shown that the electrode has a reversible potentiometric response with respect to the octahydrotriborate anion in the presence of a number of other inorganic anions. The influence of the concentration of the electrode-active material and the nature of the plasticizer in the membrane phase on the electrochemical characteristics of the fabricated sensor have been studied. The optimal composition of the ion-sensitive membrane has been found. It has been found that the developed sensor provides a wide range of detectable concentrations of(1 × 10–7…1 × 10–2) and a low detection limit (10–7.3 M). The new ISE can be recommended for direct potentiometric detection of free octahydrotriborate anions in technological aqueous solutions.

Ion-Selective Membrane Electrode for Determination of the Octahydrotriborate Anion

Ion-Selective Membrane Electrode for Determination of the Octahydrotriborate Anion

Nucleophilic Substitution Reactions in the [B3H8]- Anion in the Presence of Lewis Acids.

As a result of our study on the interaction between the octahydrotriborate anion with nucleophiles (Nu = THF, Ph3P, Ph2P-(CH2)2-PPh2 (dppe), Ph3As, Et3N, PhNH2, C5H5N, CH3CN, Ph2CHCN)) in the presence of a wide range of Lewis acids (Ti(IV), Hf(IV), Zr(IV), Al, Cu(I), Zn, Mn(II), Co(II) halides and iodine), a number of substituted derivatives of the octahydrotriborate anion [B3H7Nu] are obtained. It is found that the use of TiCl4, AlCl3, ZrCl4, HfCl4, CuCl and iodine leads to the highest product yields. In this case, it is most likely that the reaction proceeds through the formation of an intermediate [B3H7-HMXnx], which was detected by NMR spectroscopy. The structures of [Ph3P·B3H7] and [PhNH2·B3H7] were determined by X-ray diffraction.

Three-center two-electron bonds in the boranes B2H6 and B3H8− from the quantum interference perspective

In this work the nature of the three-center two-electron (3c2e) chemical bonds in the diborane (6) molecule and the octahydrotriborate anion (B3H8−) is investigated by the Generalized Product Function Energy Partitioning (GPF-EP) method using modern valence bond wave functions. The Interference Energy Analysis shows that 3c2e bonds have the same features of a 2c2e bond: interference dominates the energetic balance for the formation of the bond and the kinetic energy drop is responsible for its stabilization. Also, 3c2e are generally way more energetic than a 2c2e analogous one, because interference can occur in three different ways (multiple interference effect), rather than just in one as for the two-center bonds. Furthermore, with the GPF-EP method one could establish a more rigorous way for discussing the idea of a “supported” bond in the diborane (6) molecule.

Elucidation of the Formation Mechanisms of the Octahydrotriborate Anion (B3H8-) through the Nucleophilicity of the B-H Bond.

Boron compounds are well-known electrophiles. Much less known are their nucleophilic properties. By recognition of the nucleophilicity of the B-H bond, the formation mechanism of octahydrotriborate (B3H8-) was elucidated on the bases of both experimental and computational investigations. Two possible routes from the reaction of BH4- and THF·BH3 to B3H8- were proposed, both involving the B2H6 and BH4- intermediates. The two pathways consist of a set of complicated intermediates, which can convert to each other reversibly at room temperature and can be represented by a reaction circle. Only under reflux can the B2H6 and BH4- intermediates be converted to B2H5- and BH3(H2) via a high energy barrier, from which H2 elimination occurs to yield the B3H8- final product. The formation of B2H6 from THF·BH3 by nucleophilic substitution of the B-H bond was captured and identified, and the reaction of B2H6 with BH4- to produce B3H8- was confirmed experimentally. On the bases of the formation mechanisms of B3H8-, we have developed a facile synthetic method for MB3H8 (M = Li and Na) in high yields by directly reacting the corresponding MBH4 salts with THF·BH3. In the new synthetic method for MB3H8, no electron carriers are needed, allowing convenient preparation of MB3H8 in large scales and paving the way for their wide applications.

Nickel(II) and Iron(II) coordination compounds with octahydrotriborate(1–) anion [ML3]{B3H8}2 (M = Fe2+, Ni2+; L = bipy, phen)

Methods of synthesis have been developed for new types of promising precursors of metal borides, coordination compounds [ML3]B{3H8{2 (M = Fe2+, Ni2+; L = bipy, phen), using modified procedures of synthesis of octahydrotriborate anion. Compounds [Ni(bipy)3]B{3H8}2, [Ni (phen)3]B{3H8}2 and [Fe(phen)3]B{3H8}2 were prepared and characterized by single-crystal X-ray diffraction.

ChemInform Abstract: The Chemistry of the Octahydrotriborate Anion [B3H8

AbstractReview: 97 refs.

Guanidinium octahydrotriborate: an ionic liquid with high hydrogen storage capacity

Guanidinium octahydrotriborate, with a melting point of <−10 °C, releases >10 wt% high purity hydrogen below 100 °C.

The chemistry of the octahydrotriborate anion [B3H8

The review integrates data on the structure, methods of synthesis, reactivity, and coordination properties of the octahydrotriborate anion.

Synthesis and Characterization of the Homoleptic Octahydrotriborate Complex Cr(B3H8)2and Its Lewis Base Adducts

Solvate-free sodium octahydrotriborate, NaB3H8, is prepared on a 20 gram scale from sodium amalgam and diborane in diethyl ether. This substance, which is chemically related to borohydride-based compounds being investigated as hydrogen storage materials, is also useful for the preparation of transition-metal complexes bearing B3H8 ligands. Treatment of CrCl3 with NaB3H8 affords a thermally unstable purple liquid thought to be a chromium(III) hydride of stoichiometry CrH(B3H8)2. This hydride converts rapidly at room temperature to the chromium(II) complex Cr(B3H8)2, which adopts a square-planar structure in which four hydrogen atoms form the coordination sphere of the chromium atom. This chromium(II) species forms six-coordinate Lewis base adducts Cr(B3H8)2L2, where L is Et2O, THF, or PMe3; the first two of these adopt trans geometries, whereas the latter is cis. Volatile Cr(B3H8)2 is the first homoleptic transition-metal complex of the octahydrotriborate anion, and it is an excellent single-source precursor for the chemical vapor deposition of thin films of CrB2 at temperatures as low as 200 degrees C. Crystal structures of the new complexes are reported.

A New Class of CVD Precursors to Metal Borides: Cr(B3H8)2 and Related Octahydrotriborate Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A New Class of CVD Precursors to Metal Borides: Cr(B3H8)2 and Related Octahydrotriborate Complexes

Treatment of CrCl3 with sodium octahydrotriborate, NaB3H8, affords a thermally unstable purple liquid thought to be a chromium(III) hydride of stoichiometry CrH(B3H8)2. This hydride converts rapidly at room temperature to the chromium(II) complex Cr(B3H8)2, which adopts a square-planar structure in which four hydrogen atoms form the coordination sphere of the chromium atom. This chromium(II) species forms six-coordinate Lewis base adducts Cr(B3H8)2L2, where L is Et2O, thf, or PMe3; the first two of these adopt trans geometries, whereas the latter is cis. Volatile Cr(B3H8)2 is the first homoleptic transition metal complex of the octahydrotriborate anion, and it readily forms CrB2 thin films by CVD at 250 degrees C.

Organotransition-Metal-Mediated Borane-Cage Expansion

Attempts were made to synthesize dinuclear Group 6 metal complexes of the arachno -octahydrotriborate anion. Specifically, the dimer [CpW(CO) 3 ] 2 (Cp = m 5 -C 5 H 5 ) was employed as the metal reagent. However, the formation of dinuclear metallaborane complexes did not ensue. Rather, clean, rapid, systematic borane-cage expansion was observed. The [B 3 H 8 ] m cluster was quantitatively converted to B 5 H 9 ,[B 9 H 14 ] m , or [B 11 H 14 ] m , or both, depending on reaction conditions. Refluxing a 1:1 mixture of [B 3 H 8 ] m and [CpW(CO) 3 ] 2 in toluene or dioxane lead to the rapid, quantitative conversion of [B 3 H 8 ] m to B 5 H 9 . However, refluxing a 2:1 mixture of [B 3 H 8 ] m and [CpW(CO) 3 ] 2 in the same solvents yielded [B 9 H 14 ] m and [B 11 H 14 ] m as the primary products; when glyme was the solvent, only [B 9 H 14 ] m was observed, even after prolonged heating.

Synthesis and Reactivity of the Metallaborane Complex [Mo(CO)4B3H8]- and the Formation of Mo(CO)4(dppe)

In this laboratory exercise the octahydrotriborate anion ([B3H8]-) is synthesized from sodium borohydride (NaBH4) and iodine in diglyme under a nitrogen atmosphere, and the sodium salt is converted to the tetrabutylammonium salt by a simple metathesis. Next, the metallaborane complex [(CO)4MoB3H8]- is prepared by refluxing a solution of Mo(CO)6 and (Bu4N)B3H8 in anhydrous 1,2-dimethoxyethane (glyme) under a nitrogen atmosphere. This solution is transferred via cannula to a flask containing the solid 1,2-bis(diphenylphosphino)ethane (dppe). The ensuing formation of [Mo(CO)4(dppe)] is nearly instantaneous. The syntheses of the two metal complexes proceed in very high yield.This exercise features inert-atmosphere syntheses and multinuclear (1H, 11B, and 31P) NMR spectroscopy and is suitable for upper-level undergraduates. The skills and ideas that are taught or reinforced include a general overview of borane clusters and the isolobal analogy, handling air-sensitive solutions, and internuclear coupling in NMR spectra.

Cyano and isocyano derivatives of the octahydrotriborate anion; Molecular and crystal structures of the [(Ph 3P) 2N] + salts of [B 3H 7NCBH 3] −, [(B 3H 7) 2CN] − and [Ag(CNB 3H 7) 2] −

[Ph 3P) 2N][B 3H 7NCBH 3] is triclinic, P 1 , with 2 ion pairs in a cell of dimensions a = 9.832(3), b = 11.490(3), and c = 16.889(2) Å, α = 105.66(2), β = 92.43(2), and γ = 101.59(2)° at 185 K. Using 5255 amplitudes the structures has been refined to R = 0.059. There are 4 ion pair of [(Ph 3P) 2N][B 3H 7) 2CN] in a monoclinic unit cell, a = 17.003(4), b = 11.823(9), and c = 19.519(8) Å, β = 108.78(3)°, space group P2 1/a. R = 0.066 for 4840 reflections, again measured at 185 K. For [(Ph 3P) 2N][Ag(CNB 3H 7 2] the unit cell is a = 17.976(6), b = 11.559(3), and c = 19.20(3) Å β = 94.30(6)°, space group P2 1/c, and Z = 4.3742 reflections measured at 185 K have been used to refine to R = 0.074. The arrangements of hydrogen atoms in four of the five B 3H 7 moietes contained within these three crystal structures is common, there being one bridging-H across the B-B connectivity not involving the substituted atom.

FSGO calculations of octahydrotriborate anion and tetraborane

FSGO calculations of octahydrotriborate anion and tetraborane

FSGO calculations of octahydrotriborate anion and tetraborane

The FSGO quantum mechanical model is used to makeab initio calculations of the geometrical structures and energies of the ground state configurations of the octahydrotriborate anion, B3H8−, and tetraborane, B4H10. Both molecules are assumed to belong to theC2v symmetry point group during these computations. Comparisons with available experimental data show good agreement. B4H10 calculations are also compared with results of SCF calculations.