Systematics in the Chemistry of the Boron Hydrides

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-HMXn_x], which was detected by NMR spectroscopy. The structures of [Ph₃P·B₃H₇] and [PhNH₂·B₃H₇] were determined by X-ray diffraction.

Li(NH3)B3H8: a new ionic liquid octahydrotriborate

We report a strategy of using small cations to construct ionic liquid octahydrotriborate. The novel liquid Li(NH3)B3H8, prepared by a facile reaction of NH4B3H8 with LiH, froze below -33.4 °C and crystallized into a monoclinic unit cell with lattice parameters of a = 8.813(1) Å, b = 8.8626(1) Å, c = 8.2076(1) Å, and β = 110.1046(5)°, providing a promising functional liquid octahydrotriborate with the highest B3H8- content and lowest freezing temperature.

Design of a catalyst through Fe doping of the boron cage B10H14 for CO2 hydrogenation and investigation of the catalytic character of iron hydride (Fe-H)

The innovative catalyst Fe@B₁₀H₁₄ is designed through Fe doping of the boron cage B₁₀H₁₄ and is employed to catalyze CO₂ hydrogenation using a quantum mechanical method. First, the structure of the Fe@B₁₀H₁₄ complex is characterized through calculated ¹¹B NMR chemical shifts and Raman spectra, and the interactions between Fe and the four H atoms of the opening in the cage are analyzed, which show that various iron hydride (Fe-H) characteristics exist. Subsequently, the potential of Fe@B₁₀H₁₄ as a catalyst for the hydrogenative reduction of CO₂ in the gas phase is computationally evaluated. We find that an equivalent of Fe@B₁₀H₁₄ can consecutively reduce double CO₂ to obtain the double product HCOOH through a two-step reduction, and Fe@B₁₀H₁₂ and Fe@B₁₀H₁₀ are successively obtained. The Fe presents single-atom character in the reduction of CO₂, which is different from the common iron(ii) catalyzed CO₂ reduction. The calculated total free energy barrier of the first CO₂ reduction is only 8.79 kcal mol^-1, and that of the second CO₂ reduction is 25.71 kcal mol^-1. Every reduction reaction undergoes two key transition states TSC-H and TSO-H. Moreover, the transition state of the C-H bond formation TSC-H is the rate-determining step, where the interaction between π_{C[double bond, length as m-dash]O}* and the weak σ_Fe-H bond plays an important role. Furthermore, the hydrogenations of Fe@B₁₀H₁₂ and Fe@B₁₀H₁₀ are investigated, which aim at determining the ability of Fe-H circulation in the Fe doped decaborane complex. We find that the hydrogenation of Fe@B₁₀H₁₀ undergoes a one-step H₂-adsorbed transition state TSH-adsorb with an energy barrier of 6.42 kcal mol^-1 from Fe@B₁₀H₁₂. Comparing with the hydrogenation of Fe@B₁₀H₁₀, it is slightly more difficult for the hydrogenation of Fe@B₁₀H₁₂, where the rate-determining step is the H₂-cleaved transition state TS2H-H with an energy barrier of 17.38 kcal mol^-1.

Facile preparation and dehydrogenation of unsolvated KB3H8

A convenient route was developed to produce unsolvated KB₃H₈. This compound can release hydrogen and minor boranes by subsequent cleavage of its B–H and B–H–B bonds in the 150–250 °C temperature range. And pure K₂B₁₂H₁₂ can be prepared through KB₃H₈ pyrolysis, which is an optional approach to produce dodecaborate compounds.

Designing nonlinear optical molecule by incorporating the planar tetracoordinate unit NAl4- or CAl42- into decaborane B10H14

Molecular Incorporation is an important approach of providing novel compounds with fascinating structures. In this paper, we theoretically described the incorporation of the central planar tetracoordinate molecules NAl 4- or CAl 42- into borane cluster B 10 H 14. By molecular orbital analysis, a novel four-fold Al – H bonding interaction was found, and it contributes to the molecular incorporation. In addition, we found that the counterion Li + is critical for the neutral incorporation species, due to its small atomic radii and little positive charge. To measure the nonlinear optical (NLO) response, the static first hyperpolarizabilities (β0) were evaluated at the second-order Møller–Plesset (MP2) level. The β0 values are 1708 a.u and 8682 a.u for [ B 10 H 14⋯ NAl 4]- and [ B 10 H 14⋯ CAl 4]2-, respectively, which indicates that the charge plays a significant role on deciding the value of β0. Moreover, it is different for the change of β0 value brought by counterion Li +. Li + decreases the β0 value of [ B 10 H 14⋯ CAl 4]2-, while it increases the β0 value of [ B 10 H 14⋯ NAl 4]-, therein, the sandwich-like B 10 H 14– Li – NAl 4( I ) exhibits considerable β0 value (31,253 a.u.). This reveals that it is possible to explore high-performance NLO materials based on suitable molecular incorporation. Besides, the present study is also expected to enrich the knowledge of the planar tetracoordinate carbon chemistry and boron chemistry.

Hydrolysis of ammonia borane as a hydrogen source: fundamental issues and potential solutions towards implementation

In today's era of energy crisis and global warming, hydrogen has been projected as a sustainable alternative to depleting CO(2)-emitting fossil fuels. However, its deployment as an energy source is impeded by many issues, one of the most important being storage. Chemical hydrogen storage materials, in particular B-N compounds such as ammonia borane, with a potential storage capacity of 19.6 wt % H(2) and 0.145 kg(H2)L(-1), have been intensively studied from the standpoint of addressing the storage issues. Ammonia borane undergoes dehydrogenation through hydrolysis at room temperature in the presence of a catalyst, but its practical implementation is hindered by several problems affecting all of the chemical compounds in the reaction scheme, including ammonia borane, water, borate byproducts, and hydrogen. In this Minireview, we exhaustively survey the state of the art, discuss the fundamental problems, and, where applicable, propose solutions with the prospect of technological applications.

Ammonium octahydrotriborate (NH4B3H8): new synthesis, structure, and hydrolytic hydrogen release

A metathesis reaction between unsolvated NaB(3)H(8) and NH(4)Cl provides a simple and high-yield synthesis of NH(4)B(3)H(8). Structure determination through X-ray single crystal diffraction analysis reveals weak N-H(δ+)---H(δ-)-B interaction in NH(4)B(3)H(8) and strong N-H(δ+)---H(δ-)-B interaction in NH(4)B(3)H(8)·18-crown-6·THF adduct. Pyrolysis of NH(4)B(3)H(8) leads to the formation of hydrogen gas with appreciable amounts of other volatile boranes below 160 °C. Hydrolysis experiments show that upon addition of catalysts, NH(4)B(3)H(8) releases up to 7.5 materials wt % hydrogen.

Quantum mechanical design and structure of the Li@B10H14 basket with a remarkably enhanced electro-optical response

An innovative type of lithium decahydroborate (Li@B(10)H(14)) complex with a basketlike complexant of decaborane (B(10)H(14)) has been designed using quantum mechanical methods. As Li atom binds in a handle fashion to terminal electrophilic boron atoms of the decaborane basket, its NBO charge q (Li) is found to be 0.876, close to +1. This shows that the Li atom has been ionized to form a cation and an anion at the open end of B(10)H(14). The most fascinating feature of this Li doping is its loosely bound valence electron, which has been pulled into the cavity of the B(10)H(14) basket and become diffuse by the electron-deficient morphological features of the open end of the B(10)H(14) basket. Strikingly, the first hyperpolarizability (beta(0)) of Li@B(10)H(14) is about 340 times larger than that of B(10)H(14), computed to be 23,075 au (199 x 10(-30) esu) and 68 au, respectively. Besides this, the intercalation of the Li atom to the B(10)H(14) basket brings some distinctive changes in its Raman, (11)B NMR, and UV-vis spectra along with its other electronic properties that might be used by the experimentalists to identify this novel kind of Li@B(10)H(14) complex with a large electro-optical response. This study may evoke the possibility to explore a new thriving area, i.e., alkali metal-boranes for NLO application.