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Herein, we describe the catalytic enantioselective cross-coupling of 1,2-bisboronic esters. Prior work on group specific cross coupling is limited to the use of geminal bis-boronates. This desymmetrization provides a novel approach to prepare enantioenriched cyclopropyl boronates with three contiguous stereocenters, that could be further derivatized through selective functionalization of the carbon-boron bond. Our results suggest that transmetallation, which is the enantiodetermining step, takes place with retention of stereochemistry at carbon

The NHC copper boryl complexes [(IDipp)Cu–Bneop] (2) and [(IDipp*)Cu–Bneop] (3) (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, IDipp* = 1,3-bis(2,6-(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene, neop = (OCH2)2CMe2) were synthesised and fully characterised including single crystal X-ray structure determinations. The comparably rapid decomposition of 2, as reported previously by Sadighi and co-workers, was corroborated and can be attributed to the properties of the Bneop ligand in combination with the steric properties of the IDipp ligand. The decomposition of 2 leads predominantly to the free NHC, the diborane(4) B2neop2 (1) and, presumably, elemental copper. Minor products of this reductive decomposition are the unprecedented low-valent copper clusters [(IDipp)6Cu55] and [(IDipp)12Cu179] that were characterised by single crystal X-ray structure determinations. It is concluded that an insight in the decomposition pathways and products of copper boryl complexes is essential for the understanding of copper boryl complexes and therefor for the further development of the flourishing field of copper mediated borylation reactions.

A di(o-tolyl)borylgold complex was synthesized via the metathesis reaction of a gold alkoxide with tetra(o-tolyl)diborane(4). The resulting diarylborylgold complex exhibited a Lewis acidic boron center and a characteristic visible absorption that arises from its HOMO–LUMO excitation, which is narrower than that of a previously reported dioxyborylgold complex. The diarylborylgold complex reacted with isocyanide in a stepwise fashion to afford single- and double-insertion products and a C–C coupled product. Reactions of this diarylborylgold complex with C Created by potrace 1.16, written by Peter Selinger 2001-2019 O/N double bond species furnished addition products under concomitant formation of Au–C and B–O/N bonds, which suggests nucleophilic reactivity of the gold metal center. DFT calculations provided details of the underlying reaction mechanism, which involves an initial coordination of the CO/N bond to the boron vacant p-orbital of the diarylboryl ligand followed by a migration of the gold atom from the tetracoordinate sp3-hybridized boron center, which is analogous to the reactivity of the conventional sp3-hybridized borate species. The DFT calculations also suggested a stepwise mechanism for the reaction of this diarylborylgold complex with isocyanide, which afforded three different reaction products depending on the applied reaction conditions., A di(o-tolyl)borylgold complex added to CO/N double bond to form Au–C and B–O/N bonds. DFT calculations revealed a two-step mechanism consisting of the coordination of O/N atom to B atom followed by nucleophilic migration of Au atom.

The N–H deprotonation of the diaminodialkoxido diborane(4) pinB–Bdab (1) (pin: (OCMe2)2, dab: 1,2-(NH)2C6H4), is crucial for the electrophilic N-functionalisation towards unsymmetrical diborane(4) reagents. An N–H deprotonated diborane(4) comprises Lewis basic nitrogen atoms and at the same time Lewis acidic boron atoms. This bifunctionality governs its reactivity and structural chemistry. Whilst bases such as Na(hmds), tBuLi or Li(tmp) readily effect a single deprotonation of 1, the second deprotonation is less straightforward and cleanly only achieved with Li(tmp) as a strong but little nucleophilic base. The N–H deprotonated diborane(4) derivatives readily dimerise to give B(sp2)2B(sp3)2N2 six-membered ring Lewis base adducts. The structural chemistry of this class of compounds was studied in detail in the solid state by single crystal X-ray diffraction as well as in solution by NMR spectroscopy.

A novel and air-stable organo(hydro)diborane featuring a five-membered aryl ring supported bridging B-C-B three-centre-two-electron (3c-2e) bond has been reported. Pyrido[1,2-a]isoindole was found to undergo a stepwise BH3 addition reaction, during which a mono-BH3 adduct was formed from a electrophilic addition at the Cγ in pyrido[1,2-a]isoindole. A molecule of hydrogen was eliminated throughout the second step of addition reaction. DFT calculations indicate that the H2 evolution is concerted to the second BH3 addition rather than forming BC before the second BH3 attack.

Transition metal-free direct and base-catalyzed 1,2-diborations of arylacetylenes using pinB-BMes2 provided a syn/anti-isomeric mixture of diborylalkenes. The kinetic analysis showed that the reaction rate and isomer ratio were affected by reaction conditions and substituents on the aryl ring. DFT calculations indicated that direct addition proceeded via the interaction of acetylene-π with the BMes2 fragment. In contrast, for the base-catalyzed diboration, the previously isolated sp2–sp3 diborane and borataallene were confirmed as stable intermediates by calculations. The whole reaction pathways can be divided into the Bpin-migration and deprotonation steps, where the borataallene should be considered as a common intermediate. It should be noted that the deprotonation step is reversible and affords the kinetically less favoured isomer under the thermodynamic conditions. As a result, the composition of isomeric products, in the base-catalyzed diboration, is attributed to the small difference of activation barriers between direct and base-catalyzed systems.

An efficient synthetic method for MB3H8 (M = Li and Na) has been developed with improved yields on the basis of the investigation of the interconversion between THFB3H7 and corresponding MB3H8. The mechanism was tentatively proposed based on the understanding of the nucleophilicity of the B-H bonding pair electrons.

Lithium Borohydride (LiBH4), from the family of complex hydrides has received much attention as a potential hydrogen storage material due to its high hydrogen energy densities in terms of weight (18.5 wt%) and volume (121 kg H2 per mol). However, utilization of LiBH4 as a hydrogen carrier in off- or on-board applications is hindered by its unfavorable thermodynamics and low stability in air. In this study, we have synthesized an air stable SWCNT@LiBH4 composite using a facile ultrasonication assisted impregnation method followed by oxidation at 300 °C under ambient conditions (SWLiB-A). Further, part of the oxidized sample is treated at 500 °C under nitrogen atmosphere (SWLiB-N). Upon oxidation in air, the in situ formation of lithium borate hydroxide (LiB(OH)4) and lithium carbonate (Li2CO3) on the surface of the composite (SWLiB@LiBH4) is observed. But in the case of SWLiB-N, the surface hydroxyl groups [OH4]− completely vanished leaving porous LiBH4 with SWCNT, LiBO2 and Li2CO3 phases. Hydrogen adsorption/desorption experiments carried out at 100 °C under 5 bar H2 pressure showed the highest hydrogen adsorption capacity of 4.0 wt% for SWLiB-A and 4.3 wt% for SWLiB-N composites in the desorption temperature range of 153–368 °C and 108–433 °C respectively. The observed storage capacity of SWLiB-A is due to the H+ and H− coupling between in situ formed Li+[B(OH)4]−, Li2+[CO3]− and Li+[BH4]−. Whereas in SWLiB-N, the presence of positively charged Li and B atoms and LiBO2 acts as a catalyst which resulted in reduced de-hydrogenation temperature (108 °C) as compared to bulk LiBH4. Moreover, it is inferred that the formation of intermediate phases such as Li+[B(OH)4]−, Li2+[CO3]− (SWLiB-A) and Li+[BO2]− (SWLiB-N) on the surface of the composites not only stabilizes the composite under ambient conditions but also resulted in enhanced de- and re-hydrogenation kinetics through catalytic effects. Further, these intermediates also act as a barrier for the loss of boron and lithium through diborane release from the composites upon dehydrogenation. Furthermore, the role of in situ formed intermediates such as LiB(OH)4, Li2CO3 and LiBO2 on the stability of the composite under ambient conditions and the hydrogen storage properties of the SWCNT@LiBH4 composite are reported for the first time.

3-Dimensional porous scaffold materials can be fabricated by ice templating sheets of graphene oxide (GO) or partially reduced graphene oxide (rGO). Aqueous suspensions of GO (or rGO) can be cast into monoliths or formed as beads on cooling and the solid matrices then fashioned with either laminar or radial porosity as a result. Further, ammonia borane (AB) can be integrated into the hierarchical structures in situ in a one-step process without the requirement of melt infiltration or solution impregnation techniques. Compared to AB itself, the ensuing self-assembled beads release hydrogen at a reduced onset temperature and without volume expansion on heating, suppressing the release of diborane, borazine and ammonia. Pre-reduction of the GO matrix material (to rGO) eliminates CO/CO2 release from the composites.

Different mechanisms for [NH3BH2NH3]+[BH4]− → NH3BH3 + [NH2BH2]n and [NH4]+[BH3NH2BH3]− → NH3BH2NH2BH3 have been elucidated, which leads to the proposal of a general mechanism as below.

Due to their combined Lewis acidity and electron-donor capability, BII cations exhibit an interesting reactivity, which is almost unexplored so far. In this work, we compare the reduction in a dicationic diborane of a series of vicinal diones with different redox potentials, namely 3,5-di-tert-butylbenzoquinone, 3,4,5,6-tetrachlorobenzoquinone, 1,2-naphthalene-dione, 9,10-phenanthrene-dione, 2,2′-dichlorobenzil, benzil and 1,2-acenaphthylene-dione. The experimental work is complemented by quantum-chemical calculations, illuminating the electron-transfer step in the reactions.

Reaction of a magnesium diboranate complex with triphenylphosphine oxide provides a terminal magnesium boryl, which is itself a potent reagent for the deoxygenative reduction of Ph3PO. Computational analysis with density functional theory (DFT) indicates that B–B bond activation results from initial coordination of the PO bond of the phosphine oxide to magnesium.

Borane phosphonate (bp) is a new class of unnatural internucleotide linkages where one of the oxygens in the phosphodiester linkage is replaced by an electron deficient borane (BH3) group. These unnatural internucleotide linkages are resistant to nuclease, RNase H active and hydrophobic, which significantly enhance the cellular uptake. The bp-linked oligo can be synthesized both enzymatically and chemically. Like borane (BH3) and diborane (B2H6) reagents, the borane group (BH3) in borane phosphonate oligo retains its reactivity towards a specific substrate. BpDNA reduces metal ions, such as Au(III), Ag(I), and Pt(II), and produces the corresponding metal nanoparticles; this enables the DNA-mediated morphology control and spatial positioning of nanoparticles and DNA nanostructures. Moreover, the bp-diesters undergo oxidative substitution with various nucleophiles, such as amines, alcohols, thiols, etc., upon activation by iodine; this leads to a route for post-synthetic modification of DNA including DNA functionalization. This article discusses some of the recent studies reported on bp-oligo synthesis and its applications.

Reactions of the β-diketiminato magnesium diboranate derivative, [(BDI)Mg{pinB(n-Bu)Bpin}] (BDI = HC{(Me)CNDipp}2; Dipp = 2,6-i-Pr2C6H3), with N,N′-dialkyl and N,N′-diaryl carbodiimides provided the corresponding C-borylated magnesium borylamidinates. This reactivity occurs with the displacement of n-BuBpin and with the apparent addition of a nucleophilic {Bpin} anion to the electrophilic unsaturated carbodiimide carbon centres. In contrast, while analogous reactions of [(BDI)Mg{pinB(n-Bu)Bpin}] with N-alkyl or N-aryl aldimines and ketimines also resulted in facile displacement of n-BuBpin, they provided the organomagnesium products of {Bpin} addition to the imine nitrogen atom rather than the more electrophilic trigonal imine carbon. Computational assessment by density functional theory (DFT) indicated that, although the energetic differences are marginal, the organomagnesium products may be considered as the kinetic outcome of these reactions with respect to the generation of alternative amidomagnesium regioisomers. This latter deduction was borne out by the thermally-induced conversion of two such organomagnesium species to their C-borylated amidomagnesium isomers, both of which occur with negligible entropies of activation indicative of purely intramolecular processes. Detailed analysis by DFT of the reaction of [(BDI)Mg{pinB(n-Bu)Bpin}] with PhNCHPh indicated that B–N bond formation is initiated by attack of the imine nitrogen at the three-coordinate boron atom of the diboranate anion rather than the more crowded magnesium centre. Consistent with an effectively spontaneous reaction, the resultant cleavage of the B–B bond of the diboranate unit is accomplished via the traversal of two very modest barriers of only 8.3 and 6.7 kcal mol−1. This analysis was also supportive of a subsequent intramolecular B–N to B–C isomerisation process. Of greater general significance, however, the addition of the {Bpin}− anion to the reducible aldimine is best rationalised as a consequence of the electrophilic character of this three-coordinate boron centre rather than any intrinsic nucleophilicity associated with the B–B bond of the [pinBB(n-Bu)pin]− anion.

A novel, versatile and modular route to unsymmetrical diborane(4) derivatives bearing either two different diol moieties or one diol and one diamine moiety is presented. Utilising the very basic approach of reacting a boron nucleophile with a boron electrophile to establish the B-B bond allows a simple variation of the two individual boron moieties. The copper(i) boryl complexes used as nucleophilic boron sources are readily accessible from commercially available symmetrical diborane(4) derivatives, whilst equally readily available boron halide derivatives are used as electrophiles. Seven previously inaccessible diborane(4) derivatives were obtained and fully characterised, including single crystal X-ray structure determinations, illustrating the broad scope of the method.

Diborane(4) compounds are versatile reagents in synthetic chemistry. Generally, diboranes(4) with sp2-hybridized boron atoms react as electrophiles. By contrast, the chemistry of nucleophilic diborane(4) compounds with two sp3-hybridized boron atoms is very much underdeveloped. In this work, we systematically vary the substituents of electron-rich diborane(4) compounds with bridging guanidinate substituents. In this way, five new diboranes are synthesized and fully characterized. Using quantum chemical computations, we show that the electronic properties and reactivity of these compounds can be rationally varied by the choice of substituents. The HOMO energies, adiabatic ionization energies and proton affinities are considered as parameters to compare the chemical properties of these unusual compounds.

The thermolytic decomposition of ammonia borane (AB) is known to proceed through the polymeric coupling reaction between -BH3 and -NH3 sites of multiple ammonia borane molecules, which results in the release of hydrogen and other by-products, e.g., ammonia, diborane and borazine. The formation of these by-products concomitantly pollutes the hydrogen stream, and therefore, it is necessary to remove these gases from the product stream. In the current work, a cost effective and easy to synthesize support material, aluminium phosphate (AP), is introduced in AB thermolytic decomposition. An in situ MS study reveals that the AB and AP (w/w) loading ratio of (1 × 4) is the most promising as it is able to minimise the dehydrogenation peak temperature by 18.89 °C compared to that of pure AB. Additionally, in the presence of support material, the by-product formation of ammonia is reduced by 70.3%, with a complete suppression in borazine and diborane release. The mechanism behind the by-product suppression of supported AB has been studied through 11B MAS NMR analysis which suggests that the release of hydrogen occurs through an intermolecular homopolar B-B bonding. The thermogravimetric and kinetic study also reveals that in the case of supported AB decomposition, hydrogen release through B-B interaction is much more efficient than a B-N interaction, thus limiting the possibility of autocatalysis during the supported decomposition reaction.

Zr(BH4)4·8NH3 is considered to be a promising solid-state hydrogen-storage material, due to its high hydrogen density and low dehydrogenation temperature. However, the release of ammonia hinders its practical applications. To further reduce the dehydrogenation temperature and suppress ammonia release, here we investigated its hydrolysis process to evaluate its hydrogen generation performance. The results showed that the hydrolysis of Zr(BH4)4·8NH3 in water can generate about 1067 mL g−1 pure hydrogen in 240 min at 298 K without the release of diborane or ammonia impurity gases. With heat-assistance, the hydrogen generation rate can be significantly enhanced, and its activation energy was calculated to be 29.38 kJ mol−1. The hydrolysis mechanism was clarified. The results demonstrate that Zr(BH4)4·8NH3 may work as one promising hydrogen generation material.

Ammonia borane is a promising hydrogen storage candidate due to its high hydrogen capacity and good stability at room temperature, but there are still some barriers to be overcome before it can be used for practical applications. We present the hydrogen release from ammonia borane confined in templated microporous carbon with extremely narrow pore size distribution. Compared with neat ammonia borane, the hydrogen release temperature of ammonia borane confined in microporous carbon with a pore size of 1.05 nm is significantly reduced, starting at 50 °C and with the peak dehydrogenation temperature centred at 86 °C. The dehydrogenation kinetics of ammonia borane confined in templated microporous carbon is significantly improved and by-products including ammonia and diborane are also completely prohibited without any catalysts involved. The remarkably fast hydrogen release rate and high hydrogen storage capacity from ammonia borane confined in microporous carbon are due to the dramatic decrease in the activation energy of ammonia borane. This has been so far the best performance among porous carbon materials used as the confinement scaffolds for ammonia borane in hydrogen storage, making AB confined in microporous carbon a very promising candidate for hydrogen storage.

Fluoride substitution in LiBH4 is studied by investigation of LiBH4-LiBF4 mixtures (9:1 and 3:1). Decomposition was followed by in situ synchrotron radiation X-ray diffraction (in situ SR-PXD), thermogravimetric analysis and differential scanning calorimetry with gas analysis (TGA/DSC-MS) and in situ infrared spectroscopy (in situ FTIR). Upon heating, fluoride substituted LiBH4 forms (LiBH4-xFx) and decomposition occurs, releasing diborane and solid decomposition products. The decomposition temperature is reduced more than fourfold relative to the individual constituents, with decomposition commencing at T = 80 °C. The degree of fluoride substitution is quantified by sequential Rietveld refinement and shows a selective manner of substitution. In situ FTIR experiments reveal formation of bands originating from LiBH4-xFx. Formation of LiF and observation of diborane release implies that the decomposing materials have a composition that facilitates formation of diborane and LiF, i.e. LiBH4-xFx (LiBH3F). An alternative approach for fluoride substitution was performed, by addition of Et3N·3HF to LiBH4, yielding extremely unstable products. Spontaneous decomposition indicates fluoride substitution to have occurred. From our point of view, this is the most significant destabilization effect seen for borohydride materials so far.

A strategy for the reduction of CO2 to CO by or catalyzed by metal-free silylboranes has been proposed with the aid of density functional theory (DFT) computations. We showed that one oxygen atom of CO2 can be abstracted by silylboranes without catalysts or by diboranes in the presence of silylborane catalysts with surprisingly low free-energy barriers so that the reaction can be realized under mild experimental conditions. To achieve this, the reduction mechanism of CO2 by a hierarchy of silylboranes (R1)2BSi(R2)3 was systematically investigated. Several rules of thumb were obtained to guide the design of silylboranes with high activity toward CO2 reduction. After considering many factors, such as side reactions, the stability of the silylboranes, and the solvent effect, two silylboranes, (PFP)2BSi(CH2F)3 and Me2BSi(CH2F)3, suitable for the reduction of CO2 under mild experimental conditions were designed. The overall free-energy barriers for the reduction of CO2 by the two silylboranes are just 26.1–27.0 kcal mol−1 and 28.1–28.9 kcal mol−1, respectively, at 298.15 K in solution. We further showed that CO2 can be reduced to CO by diborane Me2BBMe2 using Me2BSi(CH2F)3 as the catalyst. The overall free-energy barrier for this catalytic reaction is just 30.6–30.7 kcal mol−1 at 298.15 K in solution.

A dinuclear copper(i) complex bearing a mesoionic carbene ligand has been prepared from the corresponding silver analogue and its structure determined spectroscopically. The results revealed that two Cu(i) halide salt molecules were bound to the carbon atoms of the pyridine-bridged bis(triazolylidene) moieties rather than the pyridine. Cyclic voltammogram measurements revealed that the two Cu(i) centres underwent a stepwise oxidation, suggesting that both the triazolylidene rings of the ligand could be on the same expanded π-conjugated system. The catalytic hydroboration of styrene derivatives with bis(pinacolato)diborane in the presence of this complex allowed for the β-selective formation of the corresponding alkylboronate esters.

The unsymmetrical diborane(4) pinB–B((MeN)2(C6H4)) reacts with [(Me3P)4Rh–X] (X = Me, OtBu) giving predominantly either [(Me3P)4Rh–Bpin] or [(Me3P)3Rh–B((MeN)2(C6H4))] depending on X. At low temperatures in the presence of excess PMe3 the unprecedented equatorial boryl complex [(Me3P)4Rh–B((MeN)2(C6H4))] is formed.

Doped ZnO films are an important class of transparent conductive oxides, with many applications demanding increased growth control and low deposition temperatures. Therefore, the preparation of B-doped ZnO films by atomic layer deposition (ALD) at 150 °C was studied. The B source was triisopropyl borate, B(OiPr)3 (TIB), which has a significantly lower vapour pressure and is a safer alternative precursor to highly toxic diborane(6), B2H6. The doping fraction (DF) of the films was varied by the ratio of ZnO and dopant ALD cycles. The electrical, structural and optical properties of the ZnO:B films were studied as a function of the dopant concentration and deposition temperature, and were compared with ZnO:Al films, where dimethylaluminium isopropoxide, [Al(CH3)2(OiPr)]2 (DMAI) and trimethylaluminium, Al2(CH3)6 (TMA) were the Al sources. A low resistivity of 3.5 mO cm was achieved for 45 nm-thick ZnO:B deposited at 150 °C with a doping fraction (DF) of 0.016, which was similar to the results obtained for ZnO:Al films prepared with DMAI and lower compared to the 8 mO cm achieved for ZnO:Al prepared with TMA at an optimized DF of 0.040. Hence TIB, as well as DMAI, outperformed the conventionally employed TMA in terms of doping efficiency at 150 °C. It was found that the optical band gap could be easily tuned over the range of [similar]3.2–3.7 eV by modifying the doping fraction.

A composite material containing ammonia borane (AB) and MOF-5 has been synthesized by the infusion method. The decomposition temperature of this composite was much less than that of pristine AB. Temperature-programmed desorption mass spectrometry onset and peak temperatures of AB dehydrogenation were 60 °C and 84 °C, respectively. The hydrogen release rate of AB inside MOF-5 was markedly increased at a safe temperature of 85 °C. The activation energy of AB/MOF-5 was shown to be 68.45 kJ mol−1. The formation of the main undesirable volatile byproducts borazine and diborane was prevented. However, ammonia was still released during dehydrogenation because of the lack of a coordinately unsaturated metal in MOF-5. We suggest that the coordinately unsaturated metal sites play the key role in preventing the escape of ammonia.

Co-electrospinning ammonia borane (AB) and polyethylene oxide (PEO) has created a unique crystal phase that promotes faster hydrogen release from AB below its melting temperature with no incubation time. Integral fibres have been produced containing 75%, 50% and 25% AB by weight. As the PEO content was increased, the onset temperature of dehydrogenation was reduced from 110 °C for pristine AB to 85 °C for the 25% AB fibres. The new phase is characterised by hydrogen bonding between the hydridic hydrogen atoms bonded to the nitrogen atom in AB and the oxygen atom in the PEO backbone. Additionally, the usual foaming of AB during hydrogen release was effectively controlled by the addition of PEO. Some impurities which accompany the hydrogen release – ammonia and diborane – are reduced, however, borazine levels in the gas stream were observed to increase during the loss of the 2nd hydrogen equivalent. Nevertheless, co-electrospun composites of AB and PEO show great promise as a safe, portable and versatile hydrogen storage material.

Borane–amine adducts (H3N·BH3, AB) in tetrahydrofuran solution were infiltrated into polypyrrole (PPy) nanotubes by a capillary effect, forming an ammonia borane (AB)@PPy combined system. This composite system combines the synergetic catalysis of nitrogen atoms with nanoconfinement in nanotubes, resulting in a significant improvement in the dehydrogenation properties. Dehydrogenation results showed that the AB loaded on PPy can release 15.3% hydrogen below 150 °C with an onset decomposition temperature as low as 48 °C. More importantly, the evolution of harmful ammonia, diborane, and borazine was entirely suppressed.

One of the major issues associated with the use of borohydride complexes for hydrogen storage is the thermodynamic stability of these materials, with the Group I and II complexes also requiring the most demanding temperatures to facilitate dehydrogenation. In recent years, the idea of modulating thermodynamic properties by combining metals with different stabilities (as monocation borohydrides) has come to light. By incorporating a cation with ionic bonding characteristics, it has been proposed that the volatile Sc borohydrides can be stabilized to an extent that diborane release is prevented. We show, using in situ IR and TG analysis, that these complexes do indeed release significant quantities of diborane, which is an irrevocable barrier to reversibility. Our findings suggest that the Group I/Sc bimetallic borohydrides are not suitable for hydrogen storage.

A twisted mono-cationic bis-benzimidazolium salt was serendipitously isolated from the dehydrative condensation of 5,6-dihydroxyl-1,3-dimesityl-benzimidazolium and 1,4-benzenediboronic acid. Subsequent deprotonation of the benzimidazolium salt led to the formation of a spiroborate-linked free bis-NHC, which was further transformed into the corresponding diborane adduct and the di-Rh complex.

Using the ab initio evolutionary algorithm for crystal structure prediction, we successfully obtained the high pressure crystal structure of BI3 with P21/c space group, which was characterized as the B2I6 dimer analogous to the diborane molecule. This structure has been supported by excellent agreement between the theoretical and experimental equations of state, X-ray diffraction data, and the positive pressure dependence of Tc. Moreover, the P21/c structure is both dynamically and mechanically stable through phonon and elastic constants calculations. Further analysis reveals a superconducting mechanism in which the vibrations of iodine atoms dominate the superconductivity of BI3. In addition, the positive pressure dependence Tc is mainly attributed to the increase of the EPC parameter λ, the logarithmic average phonon frequency ωlog, and the electronic density of states at the Fermi level N(ef).

The reduction of 2-bromo-1,3,2-diazaborole tBuNCH=CH(tBu)BBr (4c) with a potassium mirror in 1,2-dimethoxyethane afforded a non-separable 1 : 2 : 1 mixture of the compounds tBuNCH=CHN(tBu)BH (5), tBuNCH=CHN(tBu)BOCH3 (6) and {tBuNCH=CHN(tBu)B}(2)O (7). Reaction of 4c with a potassium-sodium alloy in N,N,N',N'-tetramethylethylenediamine led to 5 as the major product. 1,3,2-Diazaboroles tBuNCH=CHN(tBu)BN-Me-2 (8) and {tBuNCH=CHN(tBu)B}(2) (9) were spectroscopically identified as minor products. The treatment of 4c with potassium-sodium alloy in toluene solution in the presence of [15]crown-5 yielded a 1 : 1 mixture of 5 and the benzyl derivative tBuNCH=CHN( tBu)BCH2Ph (12). The same reaction in toluene-d(8) produced the deuterated species 5-d(1) and 12-d(7). tBuNCH=CHN(tBu)BCH3 (17) and 1,4-diazabutadiene (tBuN=CH)(2) (18) resulted from the treatment of tBuNCH=CHN(tBu)BSCH3 (15) with potassium-sodium alloy in n-hexane. In contrast to this, compound 9 was obtained as the main product of the reduction of tBuNCH=CHN(tBu)BStBu (16) under similar conditions. The reduction of the 1-bromo-2-tert-butyl-1,2-dihydro[1,3,2]diazaborolo[1,5-a]pyridine (19) smoothly produced the respective diborane(4) derivative (20) which was subjected to X-ray diffraction analysis.

The reaction between the platinum(II) bis(boryl) complex cis-[Pt(PPh3)2(Bcat)2] (cat = 1,2-O2C6H4) and the tertiary phosphines PMe3, PEt3, PMe2Ph, PMePh2 and dcpe [1,2-bis(dicyclohexylphosphino)ethane] and the phosphite P(OEt)3 afforded the new complexes cis-[Pt(PR3)2(Bcat)2] (PR3 = PMe3, PEt3, PMe2Ph or PMePh2), cis-[Pt(dcpe)(Bcat)2] and cis-[Pt{P(OEt)3}2(Bcat)2]. With PCy3 the mixed phosphine species cis-[Pt(PCy3)(PPh3)(Bcat)2] is the major product and was characterised by X-ray crystallography. With P(OMe)3 reductive elimination of B2(cat)2 and the formation of platinum(>0>) products occurs exclusively whereas with dmpe [1,2-bis(dimethylphosphino)ethane] the only identifiable product is the platinum(II) species [Pt(dmpe)2]Cl2. With dppm [bis(diphenylphosphino)methane] a reaction occurs to give a product assigned the structure cis-[Pt(dppm)(Bcat)2] or [Pt2(dppm)2(Bcat)4] but two binuclear products were isolated as minor products, namely [Pt2(PPh3)(µ-dppm)2(Bcat)(µ-Bcat)] and [Pt2(κ1-dppm)(µ-dppm)2(Bcat)(µ-Bcat)]. Both compounds were characterised by X-ray crystallography and shown to contain unusual semi-bridging Bcat groups. The reaction between [Pt(PPh3)2(η-C2H4)] and the diborane(4) compound 1,2-B2Cl2(NMe2)2 is also described which results in B–B bond oxidative addition yielding cis-[Pt(PPh3)2{BCl(NMe2)}2] and a complex to which this bis(boryl) subsequently rearranges, namely trans-[PtCl(PPh3)2{BCl(NMe2)}]. Both of these complexes were characterised by X-ray crystallography and have geometries typical of cis-bis(boryl) and trans-boryl chloride complexes respectively.

Crystal structures of 1∶1 adducts of diborane(4) compounds and the electron acceptors TCNQ and TCNE, namely B2(1,2-E2C6H4)2·TCNQ (E = O or S) and B2(1,2-E2C6H4)2·TCNE (E = O or S), have been found to show predominantly two-dimensional heteromolecular packing motifs with a variety of interlayer packings.

The chiral diborane(4) compounds B2[R,R-O2CH(CO2Me)CH(CO2Me)]2, B2(S-O2CH2CHPh)2, B2(R,R-O2CHPhCHPh)2 and B2(O2C20H12)2 (O2C20H12 = 1,7′-bi-2-naphtholate) have been synthesized. All four compounds have been characterised by X-ray crystallography, the latter as a racemate. The B–B bond oxidative-addition reactions of the first three compounds with [Pt(PPh3)2(η-C2H4)] resulted in the platinum(II) bis(boryl) complexes cis-[Pt(PPh3)2{B[R,R-O2CH(CO2Me)CH(CO2Me)]}2], cis-[Pt(PPh3)2{B(S-O2CH2CHPh)}2] and cis-[Pt(PPh3)2{B(R,R-O2CHPhCHPh)}2]; the former two were also characterised by X-ray crystallography. The platinum-catalysed diborations of a range of prochiral 1,3-dienes with the compounds B2[R,R-O2CH(CO2Me)CH(CO2Me)]2, B2(S-O2CH2CHPh)2 and B2(R,R-O2CHPhCHPh)2 were studied. Although these reactions were clean and quantitative, observed product d.e.s (measured by 1H NMR spectroscopy) were low or non-existent indicating that chirality transfer from the diborane(4) diolate groups to the diene diboration product is not efficient in these cases.

The reaction between the diborane(4) compound B2(1,2-O2C6H4)2 and either of the rhodium(I) complexes [RhCl(PPh3)3] or [{Rh(µ-Cl)(PPh3)2}2] afforded the colourless rhodium(III) bis(boryl) species [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Similar reactions have been carried out with the diborane(4) compounds B2(1,2-O2-4-ButC6H3)2, B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2, B2(1,2-O2-4-MeC6H3)2, B2(1,2-O2-3-MeOC6H3)2, B2(1,2-S2C6H4)2, B2(1,2-S2-4-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 affording analogous rhodium complexes all of which have been characterised spectroscopically. The complexes derived from the reactions with B2(1,2-O2C6H4)2 and B2(1,2-O2-3-MeC6H3)2 have also been characterised by X-ray crystallography, the structures comprising a five-co-ordinate rhodium centre with a square-based-pyramidal geometry in which the apical site is occupied by a boryl group and the phosphines are mutually trans in basal positions. Reactivity studies have also been carried out for [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Hydrolysis or alcoholysis with catechol afforded [RhH2Cl(PPh3)3] and either B2(1,2-O2C6H4)2(µ-O) or B2(1,2-O2C6H4)3 and addition of the phosphines PMe3, PEt3 and PMe2Ph afforded the new bis(boryl) compounds cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2], [RhCl(PEt3)2{B(1,2-O2C6H4)}2] and cis,mer-[RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2], the PEt3 complex having been characterised by X-ray crystallography and shown to be similar to the PPh3 complex. The iridium analogue [IrCl(PEt3)2{B(1,2-O2C6H4)}2] was also prepared from the reaction between [IrCl(PEt3)3] and B2(1,2-O2C6H4)2 and shown by X-ray crystallography to be isomorphous with the rhodium complex. Reactions between [RhCl(PPh3)2{B(1,2-O2C6H4)}2] and the phosphines PPri3, P(C6H11)3, 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2-bis(dicyclohexylphosphino)ethane (dcpe) are also described although these do not result in new rhodium boryl complexes. The reaction between [{RhCl(dppe)}2] and B2(1,2-O2C6H4)2 afforded a compound tentatively assigned as [Rh(dppe)2{B(1,2-O2C6H4)}] with analogous compounds being formed with the diborane(4) compounds B2(1,2-O2-3-MeC6H3)2 and B2(1,2-O2-4-MeC6H3)2. Finally, the reaction between [Rh(PMe3)4]Cl and the diborane(4) compound B2(1,2-O2C6H4)2 is described which affords cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2]. Analogous reactions with B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 afforded similar products.

The reactivity of the diborane(4) compounds B 2 (1,2-E 2 C 6 H 4 ) 2 (E = O or S) have been studied with respect to their ability to co-ordinate Lewis bases, specifically 4-methylpyridine (mpy) and the phosphines PMe 2 Ph and PEt 3 . Four monoadducts have been characterised by X-ray crystallography, namely B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) and B 2 (1,2-S 2 C 6 H 4 ) 2 (PEt 3 ), together with three bis adducts B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy) 2 , B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy) 2 and B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) 2 . In the former set of compounds the one base is co-ordinated to one boron centre which adopts a tetrahedral geometry, the remaining boron being trigonal planar as in the structure of the parent compound. For the bis adducts each of the two borons is co-ordinated to a mpy or phosphine with both borons tetrahedral. Bond-length changes associated with ligand co-ordination are discussed. Multinuclear solution-state NMR studies have also been performed for solutions containing B 2 (1,2-O 2 C 6 H 4 ) 2 and mpy, B 2 (1,2-S 2 C 6 H 4 ) 2 and mpy and B 2 (1,2-S 2 C 6 H 4 ) 2 and PEt 3 . All of these studies indicate that intermolecular exchange of base between the parent compound, the mono- and the bis-adducts occurs in solution together with intramolecular exchange between the two boron centres in the monoadducts. The various rates of these processes, inasmuch as they have been determined accurately, are discussed and rationalised. The monoadducts B 2 (1,2-O/S 2 C 6 H 4 ) 2 (mpy) are nominally isoelectronic with the phenonium cation.

The 1,2-dihalogenodiborane(4) compound Br(Me2N)BB(NMe2)Br 1 reacts with Li(mes)(mes = C6H2Me3-2,4,6) or LiPh to form the derivatives Br(Me2N)BB(NMe2)(mes)2, (mes)(Me2N)BB(NMe2)(mes)3, and the previously reported (synthesised by a different route) species Ph(Me2N)BB(NMe2)Ph 4 in moderate yields. Compounds 2–4 are thermally stable, colourless, crystalline solids. All compounds were characterized by X-ray crystallography and NMR spectroscopy. Their structures have B–B bond lengths that vary from 1.682(16)A in 1 to 1.717(15)A in 3. In addition, all compounds display high angles (from 58.9 to 88.7 °) between the planes at the boron atoms and short B–N distances that are near 1.39 A. The structures of 1–4 represent, apparently, the first such acyclic examples for diborane(4) derivatives of the type B2X2(NR2)2 where X = halogen or aryl group. Crystal data: 130 K: 1, Br(Me2N)BB(NMe2)Br, monoclinic, space group P21, a= 6.789(2), b= 7.720(2), c= 10.012(4), β= 103.06(3)°, Z= 2, R= 0.048 for 1109 [I > 2.0σ(I)] data; 2, Br(Me2N)BB(NMe2)(mes), monoclinic, space group C2/c, a= 24.890(14), b= 7.662(4), c= 18.500(12), β= 116.36(4)°, Z= 8, R= 0.063 for 1910 [I > 2.0σ(I)] data; 3(mes)(Me2N)BB(NMe2)(mes), orthorhombic, space group Pbcn, a= 37.983(14), b= 14.167(5), c= 12.282(4)A, Z= 12, R= 0.095 for 1829 [I > 3.0σ(I)] data; 4, Ph(Me2N)BB(NMe2)Ph, orthorhombic, space group P212121, a= 8.579(2), b= 12.920(4), c= 13.925(3)A, Z= 4, R= 0.045 for 1776 [I > 4.0σ(I)] data.

The reaction between 1,2-B2Cl2(NMe2)2 and disodium catecholate Na2[1,2-O2C6H4] affords the cyclic diborane(4) compound 1,2-B2(NMe2)2(cat) (cat=1,2-O2C6H4), whereas a similar reaction using dilithium thiocatecholate Li2[1,2-S2C6H4] affords the 1,1-isomer 1,1-B2(NMe2)2(thiocat) (thiocat=1,2-S2C6H4). Both compounds can be used to prepare unsymmetric diborane(4) species.

The reaction of diborane with the silica gel surface has been studied with Fourier transform infrared photoacoustic spectroscopy (FTIR–PAS). After a dissociative adsorption of diborane on the siloxane bridges, borane reacts with the hydroxyl groups of the silica gel surface, evolving hydrogen gas. Besides this general reaction (a), a new reaction (b) is observed, which is competitive with the direct boranation of the hydroxyl groups. The siloxane bridges act as reactive chemisorption sites, resulting in the formation of silane groups. [graphic omitted]

The platinum catalysed diboration of alkynes using the diborane(4) compound 1,2-B2Cl2(NMe2)2 affords high yields of cyclic 1-azonia-2-borata-5-borole compounds, which arise from redistribution of B–Cl and B–NMe2 bonds.

The effects of nanoconfinement on the dehydrogenation rate and reaction pathways of the eutectic LiBH4–Mg(BH4)2 have been comprehensively investigated. By means of thermal analysis, mass spectroscopy and solid state 11B MAS NMR, it has been revealed that the multistep thermal decomposition pattern of the binary LiBH4–Mg(BH4)2 has been altered in a two-step reaction and the desorption kinetics has also been significantly improved after infiltration. The formation of diborane and stable MnB12H12 intermediates of the bulk LiBH4–Mg(BH4)2 has been found to be inhibited by nanoconfinement.

Boron–nitrogen containing compounds with high hydrogen contents as represented by ammonia borane (NH3BH3) have recently attracted intense interest for potential hydrogen storage applications. One such compound is [(NH3)2BH2]B3H8 with a capacity of 18.2 wt% H. Two safe and efficient synthetic routes to [(NH3)2BH2]B3H8 have been developed for the first time since it was discovered 50 years ago. The new synthetic routes avoid a dangerous starting chemical, tetraborane (B4H10), and afford a high yield. Single crystal X-ray diffraction analysis reveals N–Hδ+⋯Hδ−–B dihydrogen interactions in the [(NH3)2BH2]B3H8·18-crown-6 adduct. Extended strong dihydrogen bonds were observed in pure [(NH3)2BH2]B3H8 through crystal structure solution based upon powder X-ray analysis. Pyrolysis of [(NH3)2BH2]B3H8 leads to the formation of hydrogen gas together with appreciable amounts of volatile boranes below 160 °C.

Metal borohydrides offer high theoretical storage capacity for solid state hydrogen storage. This work is aimed at the mechanochemical synthesis of Yb(BH4)3 from LiBH4 and YbCl3. Different synthesis routes resulted in three new compounds, LiYb(BH4)4−xClx, α-Yb(BH4)3 and β-Yb(BH4)3. Their crystal structures have been determined from lab and synchrotron powder diffraction. LiYb(BH4)4−xClx takes a primitive tetragonal structure with x = 1.0, a = 6.1729(3) A and c = 12.4155(10) A in the space group P2c (no. 112), α-Yb(BH4)3 a primitive cubic structure with a = 10.70715(15) A in the space group Pa (no. 205), and β-Yb(BH4)3 a primitive cubic structure with a = 5.44223(3) A in the space group Pmm (no. 221). Thermal decomposition properties of the materials have been investigated by in situ synchrotron radiation powder X-ray diffraction, thermo gravimetric analysis/differential scanning calorimetry and temperature programmed desorption. The decomposition product, Yb(BH4)2−xClx, adopting a primitive tetragonal structure with space group P (no. 81) was formed after release of diborane gas, and x increases with increasing temperature. A deuterated sample of this compound was synthesized for powder neutron diffraction. Rietveld refinement gave x = 0.76, a = 6.74763(2) A and c = 4.28368(2) A. Another polymorph of Yb(BH4)2−xClx was synthesized, which adopts a primitive orthorhombic structure with space group Pbca (no. 61), where x = 0.3, a = 13.20997(20) A, b = 8.26829(12) A and c = 7.44532(11) A.

Polyetheral additives were found to be efficient promoters to enhance the rate of H2-release from ammonia borane (AB) at various temperatures. In particular, tetraethylene glycol dimethyl ether (T4EGDE, 29 wt% relative to AB + T4EGDE) exhibited significantly improved activities for AB dehydrogenation, with the material-based hydrogen storage capacity of 10.3 wt% at 125 °C within 40 min. In situ FT-IR spectroscopy indicated the formation of B-(cyclodiborazanyl)amino-borohydride (BCDB), borazine, and μ-aminodiborane as gaseous byproducts. In addition, (11)B nuclear magnetic resonance (NMR) spectroscopy further revealed that diammoniate of diborane (DADB) was initially formed to give polyaminoborane as liquid and/or solid spent-fuel, consistent with previous reports. Density Functional Theory (DFT) calculations suggested that hydrogen bonding interactions between AB and a polyetheral promoter initially played an important role in increasing the reactivity of B-H bonds of AB by transferring electron density from oxygen atoms of the promoter into B-H bonds of AB. These partially activated, hydridic B-H bonds were proposed to help promote the formation of diammoniate of diborane (DADB), which is considered as a reactive intermediate, eventually enhancing the rate of H2-release from AB. In addition, our in situ solid state (11)B magic angle spinning (MAS) NMR measurements further confirmed that the rate of DADB formation from AB with a small quantity of T4EGDE was found to be much faster than that of pristine AB even at 50 °C. This metal-free method for H2-release from AB with an added, small quantity of polyethers would be helpful to develop feasible hydrogen storage systems for long-term fuel cell applications.

A novel strategy of adopting the reversible swelling effect of a promising scaffold—hypercrosslinked porous poly(styrene-co-divinylbenzene) resin (PSDB) to nanoconfine hydrogen storage materials is reported, in which nanoconfined ammonia–borane (AB) is endowed with high loading ratio and significantly improved hydrogen storage capabilities. To verify the importance of swelling behavior displayed by this polymeric scaffold in dehydrogenation, an ammonia-dissolving route (PSDB–AB (NH3)) that does not involve swelling, was performed to enable direct comparison with the methanol-dissolving route (PSDB–AB (CH3OH)). Moreover, solid-state 11B NMR measurements were employed to illustrate the different reaction mechanisms in these two PSDB-confined AB samples, where decomposition involving both the diammoniate of diborane (DADB) and linear dimer are observed for PSDB–AB (NH3) but only the latter route is seen for PSDB–AB (CH3OH), deeply demonstrating the difference of dehydrogenation properties in these two samples. Our findings establish a prospective approach via utilizing this class of polymers for promoting the design and construction of advanced energy materials with high performances.

Boron carbide nanowires, a promising class of high temperature thermoelectric nanomaterials, are synthesized by co-pyrolysis of diborane and methane in a low pressure chemical vapor deposition system via the vapor–liquid–solid growth mechanism. Nickel and iron are effective catalytic materials. The synthesis is realized at relatively lower temperatures, with 879 °C as the lowest one. Electron microscopy analysis shows that the as-synthesized nanowires have diameters between 15 and 90 nm and lengths up to 10 μm. The nanowires have single crystalline boron carbide cores and thin amorphous oxide sheaths. Both transverse faults and axial faults with fault planes as {101}h-type are observed, which could provide additional measures to tune the nanowire transport properties for better thermoelectric performance. Measurement of individual boron carbide nanowires reveals that the thermal conductivity is diameter-dependent, which indicates that boundary scattering still provides an effective approach to reduce the wire thermal conductivity for enhanced thermoelectric performance.

A novel eutectic hydrogen storage system, LiBH4·NH3–nNH3BH3, which exists in a liquid state at room temperature, was synthesized through a simple mixing of LiBH4·NH3 and NH3BH3 (AB). In the temperature range of 90–110 °C, the eutectic system showed significantly improved dehydrogenation properties compared to the neat AB and LiBH4·NH3 alone. For example, in the case of the LiBH4·NH3/AB with a mole ratio of 1 : 3, over 8 wt.% hydrogen could be released at 90 °C within 4 h, while only 5 wt.% hydrogen released from the neat AB at the same conditions. Through a series of experiments it has been demonstrated that the hydrogen release of the new system is resulted from an interaction of AB and the NH3 group in the LiBH4·NH3, in which LiBH4 works as a carrier of ammonia and plays a crucial role in promoting the interaction between the NH3 group and AB. The enhanced dehydrogenation of LiBH4·NH3/AB may result from the polar liquid state reaction environments and the initially promoted formation of the diammoniate of diborane, which will facilitate the B–H⋯H–N interaction between LiBH4·NH3 and AB. Kinetics analysis revealed that the rate-controlling steps of the dehydrogenation process are three-dimensional diffusion of hydrogen at temperatures ranging from 90 to 110 °C.

The dimethyl sulfide adduct 2(DMS) is a crystalline storage form of the unstable hydroboration reagent 9-H-9-borafluorene (2); 2(DMS) is available by the addition of DMS to either in situ generated [2](2) or 1,2-(2,2'-biphenylylene)diborane(6) (7).

An ab initio study of an isomer of diborane(4) [B2H4] has been carried out at MP2/aug-cc-pVTZ to investigate the ground-state properties of this unusual molecule, a derivative of which has been described in the recent literature. The geometric, electronic and orbital characteristics of B2H4(4) have been analyzed using AIM, NBO, and ELF methodologies. A region with a high concentration of electron density is located near and along the B-B bond, on the opposite side of this bond relative to the bridging H atoms. This site serves as an electron-donor site to electrophiles, resulting in hydrogen-bonded complexes of B2H4 with proton donors HF, HNC, HCl, HCN, and HCCH, and a van der Waals complex with H 2. These complexes have C2v symmetry and stabilization energies that vary from 2 to 27 kJ mol-1. The SAPT2 energy decomposition analysis shows that the relative importance of the various terms that contribute to the interaction energy depends on the strength of the interaction. © the Owner Societies 2011.

Molecular complexes of Lewis acid-base pairs can be used to activate molecular hydrogen for applications ranging from hydrogen storage for fuel cells to catalytic hydrogenation reactions. In this paper, we examine the factors that determine the thermodynamics of hydrogen activation of a Lewis acid-base pair using the pedagogical examples of ammonia borane (NH3BH3, AB) and ammonium borohydride ([NH4][BH4], ABH2). At ambient temperatures, ABH2 loses hydrogen to form the Lewis acid-base complex AB, suggesting that free energy drives the reaction to release hydrogen. However, direct measurement of the reaction enthalpy is not straightforward given the complex decomposition pathways leading to the formation of the diammoniate of diborane ([NH3BH2NH3][BH4], DADB). In this work, we compare two approaches for deriving the thermodynamic relationships among AB, DADB, and ABH2.