Borane System Research Articles

Unary Au Nanocrystal with Prestored Electrons and Intrinsic Low Hole-Injected Potential for Low-Triggering Potential Electrochemiluminescence.

Screening a novel electrochemiluminescence (ECL) system and lowering the ECL triggering potential are essential to ECL evolution. Herein, the near-infrared (NIR) ECL system with low-triggering potential ECL was constructed with weakly reductive tert-butylamine borane as coreactant and mercaptosuccinic acid/citrate (MSA/Cit)-capped Au (MSA/Cit@AuNCs) as luminophores. Toxic-element-free and dual-ligand MSA/Cit@AuNCs were prepared via ligand exchange and utilized as a model for developing unary metal NCs-based luminophores with more enhanced ECL performance than monoligand Au nanocrystals (AuNCs), which exhibited a two hole-injected process at around 0.48 and 0.80 V, respectively. Beneficial to the intrinsic low hole-injected potential of AuNCs, MSA/Cit@AuNCs exhibited similar low-triggering ECL potential at around 0.57 V with the participation of series coreactants or not, originating from the recombination of an internal prestored electron within the conduction band (CB) and electroinjected holes at around 0.25 V. Furthermore, the enhanced low-triggering potential around 0.57 V and NIR ECL around 835 nm of MSA/Cit@AuNCs was eventually obtained with the reductive tert-butylamine borane or N2H4·H2O containing a -C-N single-bond structure merely as coreactant. The low-triggering potential ECL of MSA/Cit@AuNCs/tert-butylamine borane system at 0.57 V can be harnessed to selectively determine a carcinoembryonic antigen (CEA) with one linear range spanning from 2 to 20000 fg/mL and a limit of detection of 0.33 fg/mL (S/N = 3). This study will contribute to a more comprehensive understanding of the ECL mechanism in terms of both regulating NCs and selecting coreactants.

The Possible Aromatic Conjugation via the Different Edges of (Car)Borane Clusters: Can the Relationship Between 3D and 2D Aromatic Systems Be Reconciled?

The possible aromatic conjugation between 3D and 2D aromatic units is in the focus since the synthesis of benzocarborane. It has been showed that in the 3D aromatic icosahedral 1,2-dicarba-closo-dodecaborane systems fused with 2D aromatic rings a global 3D/2D aromaticity does not exist. Despite this fact during the last years several studies proposed interactions between 2D and 3D moieties. Herein, while tuning the size and the effective charge of the (car)borane systems, we demonstrate that global aromatic character can be excluded in any investigated cases, and the detectable conjugative properties can be explained the effect of the well-known negative hyperconjugation.

Deoxygenative cross-coupling of aryl ketones with (Hetero)arenes mediated by a TiCl4/Ammonia borane system

A simple and mild protocol for the direct deoxygenative coupling of aryl ketones with electron-rich (hetero)arenes to construct the C(sp2)−C(sp3) bond was achieved, which was mediated by TiCl4 and by using ammonia borane (AB) as the reductant. This strategy provides a novel protocol for the synthesis of unsymmetrical diaryl- and triarylmethanes.

Theoretical Understanding on the Facilitated Photoisomerization of a Carbonyl Supported Borane System.

Boron compound BOMes2 containing an internal B-O bond undergoes highly efficient photoisomerization, followed by sequential structural transformations, resulting in a rare eight-membered B, O-heterocycle (S. Wang, et al. Org. Lett.2019, 21, 5285-5289). In this work, the detailed reaction mechanisms of such a unique carbonyl-supported tetracoordinate boron system in the first excited singlet (S1) state and the ground (S0) state were investigated by using the complete active space self-consistent field and its second-order perturbation (MS-CASPT2//CASSCF) method combined with time-dependent density functional theory (TD-DFT). Moreover, an imine-substituted tetracoordinated organic boron system (BNMes2) was selected for comparative study to explore the intrinsic reasons for the difference in reactivity between the two types of compounds.Steric factorwasfound to influence the photoisomerization activity of BNMes2 and BOMes2. These results rationalize the experimental observations and can provide helpful insights into understanding the excited-state dynamics of heteroatom-doped tetracoordinate organoboron compounds, which facilitates the rational design of boron-based materials with superior photoresponsive performances.

Small molecule activation and dehydrogenation of an amine–borane system using frustrated Lewis pairs

Small molecule activation and dehydrogenation of an amine–borane system using frustrated Lewis pairs

Carbon Monoxide Coupling Reactions via a Frustrated Lewis Pair-Derived η2-Formyl Borane.

The η2-formyl borane system 3 is readily available by carbonylation of the vicinal P/BH frustrated Lewis pair (FLP) 1. It serves as a frustrated C/B Lewis pair toward carbon dioxide or phenylisocyanate. In the presence of B(C6F5)3, it forms the coupling product between two CO-derived units. The resulting compound 13 rearranged to a doubly O-borylated endiolate, with both of the central carbon atoms originating from carbon monoxide. The subsequent treatment with a silane gave a rare macrocyclic silicon endiolate.

An Amine-Borane System Featuring Room-Temperature Dehydrogenation and Regeneration.

Amine-borane complexes have been extensively studied as hydrogen storage materials. Herein, we report a new amine-borane system featuring a reversible dehydrogenation and regeneration at room temperature. In addition to high purity H2 , the reaction between ethylenediamine bisborane (EDAB) and ethylenediamine (ED) leads to unique boron-carbon-nitrogen 5-membered rings in the dehydrogenation product where one boron is tricoordinated by three nitrogen atoms. Owing to the unique cyclic structure, the dehydrogenation product can be efficiently converted back to EDAB by NaBH4 and H2 O at room temperature. This finding could lead to the discovery of new amine boranes with potential usage as hydrogen storage materials.

An Amine–Borane System Featuring Room‐Temperature Dehydrogenation and Regeneration

AbstractAmine–borane complexes have been extensively studied as hydrogen storage materials. Herein, we report a new amine–borane system featuring a reversible dehydrogenation and regeneration at room temperature. In addition to high purity H2, the reaction between ethylenediamine bisborane (EDAB) and ethylenediamine (ED) leads to unique boron–carbon–nitrogen 5‐membered rings in the dehydrogenation product where one boron is tricoordinated by three nitrogen atoms. Owing to the unique cyclic structure, the dehydrogenation product can be efficiently converted back to EDAB by NaBH4 and H2O at room temperature. This finding could lead to the discovery of new amine boranes with potential usage as hydrogen storage materials.

Tripodal P3XFe-N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion.

Terminal dinitrogen complexes of iron ligated by tripodal, tetradentate P3X ligands (X = B, C, Si) have previously been shown to mediate catalytic N2-to-NH3 conversion (N2RR) with external proton and electron sources. From this set of compounds, the tris(phosphino)borane (P3B) system is most active under all conditions canvassed thus far. To further probe the effects of the apical Lewis acidic atom on structure, bonding, and N2RR activity, Fe-N2 complexes supported by analogous group 13 tris(phosphino)alane (P3Al) and tris(phosphino)gallane (P3Ga) ligands are synthesized. The series of P3XFe-N2[0/1-] compounds (X = B, Al, Ga) possess similar electronic structures, degrees of N2 activation, and geometric flexibility as determined from spectroscopic, structural, electrochemical, and computational (DFT) studies. However, treatment of [Na(12-crown-4)2][P3XFe-N2] (X = Al, Ga) with excess acid/reductant in the form of HBArF4/KC8 generates only 2.5 ± 0.1 and 2.7 ± 0.2 equiv of NH3 per Fe, respectively. Similarly, the use of [H2NPh2][OTf]/Cp*2Co leads to the production of 4.1 ± 0.9 (X = Al) and 3.6 ± 0.3 (X = Ga) equiv of NH3. Preliminary reactivity studies confirming P3XFe framework stability under pseudocatalytic conditions suggest that a greater selectivity for hydrogen evolution versus N2RR may be responsible for the attenuated yields of NH3 observed for P3AlFe and P3GaFe relative to P3BFe.

The structural phase transition of ammonia borane under high pressure

We have systematically studied the high-pressure (up to 100 GPa) behavior of ammonia borane at 0 K using particle optimization algorithm combined with the first principles calculation. The long-unsolved high-pressure structures and a complete phase transition sequence were obtained: P63mc→Pmn21→P21(Z = 2)→P21(Z = 4)→C2/m→P21/m, and the phase transition pressures are 1.23, 2.77, 11.9, 13.8, 22.34 GPa, respectively. The lack of imaginary phonon frequency effectively proves the rationality and dynamic stability of the above structures. The Raman modes calculated by density functional theory (DFT) reveals the evolution of the vibration mode under pressure, which is in good agreement with the experiment results. The analysis of dihydrogen bonds in ammonia borane shows the bonding mechanism of different high-pressure phase structures. Our research not only enriches the high-pressure phase structure of the ammonia borane system but also provides essential information for hydrogen storage materials.

Direct Experimental Observation of in situ Dehydrogenation of an Amine-Borane System Using Gas Electron Diffraction.

In situ dehydrogenation of azetidine-BH3, which is a candidate for hydrogen storage, was observed with the parent and dehydrogenated analogue subjected to rigorous structural and thermochemical investigations. The structural analyses utilized gas electron diffraction supported by high-level quantum calculations, while the pathway for the unimolecular hydrogen release reaction in the absence and presence of BH3 as a bifunctional catalyst was predicted at the CBS-QB3 level. The catalyzed dehydrogenation pathway has a barrier lower than the predicted B-N bond dissociation energy, hence favoring the dehydrogenation process over the dissociation of the complex. The predicted enthalpy of dehydrogenation at the CCSD(T)/CBS level indicates that mild reaction conditions would be required for hydrogen release and that the compound is closer to thermoneutral than linear amine boranes. The entropy and free energy change for the dehydrogenation process show that the reaction is exergonic, energetically feasible, and will proceed spontaneously toward hydrogen release, all of which are important factors for hydrogen storage.

Designing metal-free frustrated Lewis pairs for dihydrogen activation based on a carbene–borane system

Activation of small molecules by metal-free frustrated Lewis pairs (FLPs) is gaining much attention. In this regard, quantum chemical calculations have been carried out in benzene medium to design some intramolecular FLPs based on a carbene–borane system for activation of dihydrogen. Different carbenes, such as normal, abnormal and remote, has been considered in designing these FLPs. The designed FLPs are found to have lower activation barriers compared to the previously reported analogous systems. A FLP having a remote carbene is found to have the lowest activation barrier. However, the reversibility is most pronounced in case of normal carbene based FLPs, having a lower aromatization effect. The electronic feature associated with the activation process has been thoroughly studied and it is found that the synergism between donation and back-donation is responsible for activation of the HH bond.

Reorientational Motions and Ionic Conductivity in (NH4)2B10H10 and (NH4)2B12H12

We investigated molecular dynamics in two ammonium borane systems from the group of promising ion conductors. The investigation was performed by means of 1H and 11B NMR spectroscopy and spin–lattice relaxation techniques. We identified two reorientational processes, the rotations of NH4 units that are present already at low temperatures and rotations of large boron cages, B10H10 or B12H12, which are thermally activated and become prominent above 250 K. Activation energies for these processes were determined. In addition, solid-state ion conductivity measurements were conducted to determine poor NH4+ conductivity of both systems.

Hydrogen liberation from the hydrolytic dehydrogenation of hydrazine borane in acidic media

Addressed herein, the hydrolytic dehydrogenation of hydrazine borane (NH4BH3, HB) was reported in acidic media using nitric acid (HNO3) as a catalyst at room conditions. The aqueous hydrazine borane was treated with HNO3 solution in different concentrations to liberate H2. Besides, kinetic data were collected to idetificate the activation parameters, the effect of temperature, acid and hydrazine borane concentrations on the hydrogen production for the hydrolytic dehydrogenation of hydrazine borane in acidic media. It can be said that the acid catalyzed hydrazine borane system can be regarded as a simple system for hydrogen production.

General H2 Activation Modes for Lewis Acid–Transition Metal Bifunctional Catalysts

A general mechanism for H2 activation by Lewis acid–transition metal (LA-TM) bifunctional catalysts has been presented via density functional theory (DFT) studies on a representative nickel borane system, (PhDPBPh)Ni. There are four typical H2 activation modes for LA-TM bifunctional catalysts: (1) the cis homolytic mode, (2) the trans homolytic mode, (3) the synergetic heterolytic mode, and (4) the dissociative heterolytic mode. The feature of each activation mode has been characterized by key transition state structures and natural bond orbital analysis. Among these four typical modes, (PhDPBPh)Ni catalyst most prefers the synergetic heterolytic mode (ΔG‡ = 29.7 kcal/mol); however the cis homolytic mode cannot be totally disregarded (ΔG‡ = 33.7 kcal/mol). In contrast, the trans homolytic mode and dissociative heterolytic mode are less feasible (ΔG‡ = ∼42 kcal/mol). The general mechanistic picture presented here is fundamentally important for the development and rational design of LA-TM catalysts in the f...

Cobalt-bis(imino)pyridine complexes as catalysts for hydroalumination-isomerisation of internal olefins.

The insertion of α- and internal octenes (hydroalumination) and chain walking isomerisation at di-n-octylaluminium hydride [Al(Oct)2H], catalysed by bis(imino)pyridine-Co complexes has been investigated by NMR spectroscopy. The Co-based catalysts promote efficient hydroalumination of 1-octene. Internal olefins are partially hydroaluminated, with isomerisation to the primary alkyls, but the catalyst responsible appears to deactivate rapidly. The reaction between the Co precatalysts and [Al(Oct)2H] generates a Co-hydride species, likely to be a hydride bridged dinuclear Co and Al complex. This species is reactive towards α-olefins but inert towards internal olefins. In contrast to hydroalumination, the catalysts promote efficient hydroboration, where insertion and isomerisation of internal octenes goes to completion. The differences between the systems may be partially ascribed to formation of an active mononuclear Co catalyst in the borane system versus a less active Co/Al dinuclear complex in hydroalumination.

Dehydrogenation of ammonia borane catalyzed by pristine and defective h-BN sheets

The dehydrogenation of pristine and defective h-BN sheets-supported ammonia borane (AB) systems is investigated by the first-principles method. The results show that nitrogen or boron atoms at the edges of vacancies are used as hydrogen acceptors which plays a crucial role in the process of dehydrogenation between the defective h-BN sheets and AB. The energy barriers to the transfer of hydrogen from AB to the defective h-BN sheets are low and the processes are significantly exothermic, indicating that these reactions are thermodynamically favorable. The hydrogenated defective h-BN sheets (protonic and hydridic hydrogens transfer from AB to the defective h-BN sheets) further react with AB to release H2 with low reaction barriers. Our theoretical study demonstrates that the defective h-BN sheets can be the effective metal-free catalysts. Furthermore, the potential advantage of such dehydrogenation process is the fact that no other elements are being introduced into the system.

Elusive Silane–Alane Complex [SiH⋅⋅⋅Al]: Isolation, Characterization, and Multifaceted Frustrated Lewis Pair Type Catalysis

AbstractThe super acidity of the unsolvated Al(C6F5)3 enabled isolation of the elusive silane–alane complex [SiH⋅⋅⋅Al], which was structurally characterized by spectroscopic and X‐ray diffraction methods. The Janus‐like nature of this adduct, coupled with strong silane activation, effects multifaceted frustrated‐Lewis‐pair‐type catalysis. When compared with the silane–borane system, the silane–alane system offers unique features or clear advantages in the four types of catalytic transformations examined in this study, including: ligand redistribution of tertiary silanes into secondary and quaternary silanes, polymerization of conjugated polar alkenes, hydrosilylation of unactivated alkenes, and hydrodefluorination of fluoroalkanes.

Exciplex emission and decay of co-deposited 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane organic light-emitting devices with different electron transporting layer thicknesses

Highly efficient fluorescence organic light-emitting diodes (OLEDs) based on the mixed 4,4′,4″-tris[3-methylphenyl(phenyl)amino]triphenylamine:tris-[3-(3-pyridyl)mesityl]borane (1:1) system are reported. The electroluminescence due to the exciplex emission is red shifted when the thickness of the electron-transporting layer increases. The prepared OLEDs achieve a low turn-on voltage of 2.1 V, a high current efficiency of 36.79 cd/A, and a very high luminescence of 17 100 cd/m2, as well as a low efficiency roll-off. The current efficiency of the optimized OLED is maintained at more than 28.33 cd/A up to 10 000 cd m−2. The detailed recombination mechanism of the prepared OLEDs is investigated by the transient electroluminescence method. It is concluded that there are no contributions from trapped charges and annihilations of triplet-triplet excitons to the detected electroluminescence.

Catalytic role of borane and alane in hydrogen release from cyclic amine adducts CnH2n+1N·XH3 [X = B, Al; n = 2–5]: a theoretical interpretation

The reaction pathways for H2 release from cyclic amine–alane adducts in the presence and absence of alane (AlH3) are investigated and the associated potential energy surfaces are constructed by employing the composite G4MP2 method. The computed Gibbs free energy change values are potential proof of the thermodynamic feasibility of the unimolecular dehydrogenation reactions. Unlike cyclic amine–borane adducts, the unimolecular dehydrogenation barrier in cyclic amine–alane adducts is found to be lower than the Al–N bond dissociation energy in all cases but one. The calculated results clearly demonstrate that alane plays a significant catalytic role in H2 release from cyclic amine–alane adducts. The catalytic effect of molecular borane (BH3) on the dehydrogenation of cyclic amine–borane adducts is also investigated and it is observed that AlH3 exhibits a larger catalytic effect than BH3. A systematic comparison of the unimolecular as well as catalyzed H2 loss from cyclic amine–alane and amine–borane systems reveals that the former is a better candidate for releasing molecular hydrogen than the latter.