Presence Of Diborane Research Articles

Predicting Dinitrogen Coupling with a Series of Small Molecules Catalyzed by a Pincer Complex.

Due to consumption of more than 2% of the world's annual energy supply by Haber-Bosch process and the strongest triple bond (N≡N) in nature, directly coupling N2 with small molecules is particularly important and challenging, let alone in a catalytic fashion. Here we first demonstrate that a NNN-type pincer phosphorus complex could act as a catalyst to couple dinitrogen with a series of small molecules including carbon dioxide, formaldehyde, N-ethylidenemethylamine, and acetonitrile in the presence of diborane(4) under a mild condition by theoretical calculations. N2 fixation proceeds via a stepwise mechanism involving initial N2 activation by diborane(4), followed by intramolecular isomerization to a key intermediate (zwitterion). Such a zwitterion can be used to couple a series of small molecules with activation barriers of 23.5-25.2 kcal mol-1 . All these findings could be particularly useful for main group chemistry aimed at N2 activation.

Borane–Aluminum Surface Interactions: Enhanced Fracturing and Generation of Boron–Aluminum Core–Shell Nanoparticles

We present an experimental and theoretical study of borane–aluminum surface interactions that lead to rapid production of aluminum nanoparticles when Al balls are milled in the presence of diborane or pentaborane. Mass spectrometry was used to probe reactions of the boranes with aluminum fracture surfaces produced by milling collisions, which also generate local, transient high temperatures. Density functional theory was used to examine the interactions between a model aluminum surface and diborane and pentaborane, providing insight into the energetics of the first steps in the process that ultimately enables nanoparticle production. Further insight into the surface chemistry was obtained by analyzing the nanoparticles with X-ray photoelectron spectroscopy, scanning transmission electron microscopy with both electron-energy-loss and energy-dispersive X-ray spectroscopies, and dynamic light scattering. Particles were found to have fcc aluminum cores, capped by a ∼2-nm-thick shell, rich in both boron and hy...

High density and taper-free boron doped Si1−xGex nanowire via two-step growth process

The authors study Au catalyzed chemical vapor growth of Si1−xGex alloyed nanowires in the presence of diborane, serving as a dopant precursor. Our experiments reveal that introduction of diborane has a significant effect on doping and morphology. Boron exposure poisons the Au catalyst surface, suppresses catalyst activity, and causes significantly tapered wires, as a result of conformal growth. The authors develop here a two-step method to obtain high density and taper-free boron doped Si1−xGex alloy nanowires. The two-step process consists of: (1) growth of a small undoped Si1−xGex section and (2) introduction of diborane to form a boron doped Si1−xGex section. The catalyst preparation step remarkably influences wire yield, quality and morphology. The authors show that dopant-ratio influences wire resistivity and morphology. Resistivity for high boron doped Si1−xGex nanowire is 6 mΩ-cm. Four probe measurements show that it is possible to dope Si1−xGex alloy nanowires with diborane.

Formation and hydrogen release of hydrazine bisborane: transfer vs. attachment of a borane

The reactivity of hydrazine in the presence of diborane has been investigated using ab initio quantum chemical computations (MP2 and CCSD(T) methods with the aug-cc-pVTZ basis set). Portions of the relevant potential energy surface were constructed to probe the formation mechanism of the hydrazine diborane (BH(3)BH(3)NH(2)NH(2)) and hydrazine bisborane (BH(3)NH(2)NH(2)BH(3)). The differences between both adducts are established. The release of hydrogen molecules from hydrazine bisborane adducts has also been characterized. Our results suggest that the BH(3)NH(2)NH(2)BH(3) adduct, which has been prepared experimentally, is formed from the starting reactants hydrazine + diborane. The observed adduct is produced by a transfer of a BH(3) group from BH(3)BH(3)NH(2)NH(2) rather than by the direct attachment of a separate BH(3) group, generated by predissociation of diborane, to BH(3)NH(2)NH(2).

Simple Method of Preparing Graphene Flakes by an Arc-Discharge Method

Arc discharge between graphite electrodes under a relatively high pressure of hydrogen yields graphene flakes generally containing 2−4 layers in the inner wall region of the arc chamber. The graphene flakes so obtained have been characterized by X-ray diffraction, atomic force microscopy, transmission electron microscopy, and Raman spectroscopy. The method is eminently suited to dope graphene with boron and nitrogen by carrying out arc discharge in the presence of diborane and pyridine respectively.

The effect of the NH2 substituent on NH3: hydrazine as an alternative for ammonia in hydrogen release in the presence of boranes and alanes

Potential energy surfaces for H(2) release from hydrazine interacting with borane, alane, diborane, dialane and borane-alane were constructed from MP2/aVTZ geometries and zero point energies with single point energies at the CCSD(T)/aug-cc-pVTZ level. With one borane or alane molecule, the energy barrier for H(2)-loss of approximately 38 or 30 kcal mol(-1) does not compete with the B-N or Al-N bond cleavage ( approximately 30 or approximately 28 kcal mol(-1)). The second borane or alane molecule can play the role of a bifunctional catalyst. The barrier energy for H(2)-elimination is reduced from 38 to 23 kcal mol(-1), or 30 to 20 kcal mol(-1) in the presence of diborane or dialane, respectively. The mixed borane-alane dimer reduces the barrier energy for H(2) release from hydrazine to approximately 17 kcal mol(-1). A systematic comparison with the reaction pathways from ammonia borane shows that hydrazine could be an alternative for ammonia in producing borane amine derivatives. The results show a significant effect of the NH(2) substituent on the relevant thermodynamics. The B-N dative bond energy of 31 kcal mol(-1) in NH(2)NH(2)BH(3) is approximately 5 kcal mol(-1) larger than that of the parent BH(3)NH(3). The higher thermodynamic stability could allow hydrazine-borane to be used as a material for certain energetic H(2) storage applications.

Morphology of germanium nanowires grown in presence of B2H6

We study the Au-catalyzed chemical vapor growth of germanium (Ge) nanowires in the presence of di-borane (B2H6), serving as doping precursor. Our experiments reveal that, while undoped Ge nanowires can be grown epitaxially on Si(111) substrates with very long wire lengths, the B2H6 exposure renders the Ge nanowires significantly tapered. As we describe here, this peculiar morphology stems from the combination of the acicular, one-dimensional nanowire growth and a dramatically enhanced, B-induced conformal Ge deposition. The combination of acicular and conformal Ge growth mechanisms results in cone-shaped Ge nanostructures.

Chemical and phase transformations in the systems hydrogen-sorbing intermetallic compound-diborane

The reactions of the intermetallic compounds CeFe2, CeCo2, and λ3-ScFe2 with B2H6 at 4.8×103 Pa, 293-573 K, and various contact times were studied. CeFe2 decomposes in the presence of diborane to give CeH1.9-2.2, Ce2Fe17H8-10, α-Fe, CeCo2 decomposes into the cerium trihydride CeH2.7-2.8 and α-Co, whereas λ3-ScFe2 forms an ScFe2H0.4-0.5 hydride phase. Therewith, with CeFe2 and CeCo2, diborane decomposes into solid nonvolatile X-ray amorphous various-composition compounds (BH mn , as well as H2 and B5H9, while with λ3-ScFe2, into H2, B4H10, B5H9, B5H11, and (BH m) n .

Selective reduction of less reactive carbonyl groups in the presence of diborane and sodium bisulfite on silica gel

The less reactive carbonyl group of a mixture of reducible groups of carbonyl compounds was preferentially reduced with diborane on silica gel by first forming an adduct of the more reactive carbonyl group with sodium bisulfite. For example, 4-acetylbenzaldehyde could be converted to 4-(1-hydroxylethyl)benzaldehyde in 93% selectivity; in a mixture of 4-phenyl-acetophenone and 4-phenylbenzaldehyde, biphenylethanol was preferentially formed in 95% yield with 16% yield of 4-phenylbenzyl alcohol. Silica gel and sodium bisulfite were essential for this selective reaction. Aliphatic and aromatic aldehydes and unhindered cyclohexanones could be selectively protected by this method. Keywords: sodium bisulfite, silica gel, carbonyl compound, selective reduction, diborane.

Improved β-SiC heteroepitaxial films using off-axis Si substrates

All β-SiC films grown using on-axis (001) Si substrates that have been examined with transmission electron microscopy exhibit a high density of interfacial twins, stacking faults, and antiphase disorder. The antiphase boundaries can be decorated by chemical etching, sputter etching, wet oxidation, and β-SiC growth in the presence of diborane. All traces of antiphase disorder are eliminated when the heteroepitaxial growth is carried out on vicinal (001) Si substrates that are tilted 2° about a 〈110〉 axis. In addition, growth on the off-axis Si produces β-SiC films that are significantly smoother than on-axis films. The density of stacking faults is apparently unaffected by growth on the off-axis substrates.

Reduction of N-acyl,N′-tosylhydrazines with diborane : A simple, convenient procedure for the conversion of the carboxylic to the methyl group

Aliphatic tosylhydrazides upon treatment with diborane followed by alkaline hydrolysis yield aliphatic hydrocarbons. Aromatic hydrocarbons are produced when aromatic tosylhydrazides undergo heating in presence of diborane and are subsequently oxidated by KIO 4. A discussion on the structures of intermediate products is reported.

Growth and Characterization of Polycrystalline Silicon

Polycrystalline silicon is deposited by pyrolysis of silane in an rf heated epitaxial reactor. The grains exhibit a fibrous microstructure having an 〈110〉 preferred orientation in the growth direction. Growth is inhibited in the presence of excess arsine and accelerated in the presence of diborane. The results are explained in terms of catalysis and poisoning of surface adsorption sites responsible for reaction. A simple model for current conduction in polycrystalline silicon is described based on grain size, grain doping, and effective barrier height due to the grain boundary. This model satisfactorily explains the observed temperature dependence of the resistivity of undoped films and also the large values of resistivity which are observed for dopant concentrations .

The Gas Phase Photolysis of Hexafluoroacetone in the Presence of Diborane

AbstractThe photolysis of hexafluoroacetone with 3130 Å light in the presence of diborane has been investigated. Major products are CO, H2, CF3H, and C2F6, but all of the fluoroform is produced by secondary H‐atom abstraction from products of the photolysis, possibly an addition product formed at the walls between CF3 and BH2. A reaction mechanism is presented involving deactivation of the excited singlet and triplet states of the hexafluoroacetone molecule with simultaneous photosensitized diborane dissociation as the primary source of molecular hydrogen.

Organoboron compounds—XVIII Alkylbromoboranes and relative disproportionation tendencies of alkylhaloboranes

The disproportionation tendencies of alkylbromoboranes are significantly different from those of the corresponding alkylchloro and alkylfluoro compounds. Alkyldibromoboranes undergo slow thermal disproportionation to boron bromide and trialkylboranes on fractional distillation while alkyldichloro- and difluoroboranes are completely resistant to disproportionation under the same conditions. Dialkylbromoboranes are completely resistant to thermal disproportionation of dialkylfluoroboranes. That these differences in disproportionation tendencies are the result of thermodynamic rather than kinetic factors has been shown by equilibration experiments. Primary aklyldibromoboranes, dialkylbromoboranes or mixtures thereof are conveniently prepared in high yields by the reaction of appropriate stoichiometric amounts of boron bromide with primary trialkylboranes at 140° or above. Tri isopropylborane, even in the presence of diborane, does not react with boron bromide until extensive isomerization of isopropyl to n-propyl groups has occurred. Tri- s-butylborane reacts with only partial isomerization to give appreciable yields of pure di- s-butylbormoborane.