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Despite there being numerous examples of f‐element compounds supported by cyclopentadienyl, arene, cycloheptatrienyl, and cyclooctatetraenyl ligands (C5–8), cyclobutadienyl (C4) complexes remain exceedingly rare. Here, we report that reaction of [Li2{C4(SiMe3)4}(THF)2] (1) with [U(BH4)3(THF)2] (2) gives the pianostool complex [U{C4(SiMe3)4}(BH4)3][Li(THF)4] (3), where use of a borohydride and preformed C4‐unit circumvents difficulties in product isolation and closing a C4‐ring at uranium. Complex 3 is an unprecedented example of an f‐element half‐sandwich cyclobutadienyl complex, and it is only the second example of an actinide‐cyclobutadienyl complex, the other being an inverse‐sandwich. The U−C distances are short (av. 2.513 Å), reflecting the formal 2− charge of the C4‐unit, and the SiMe3 groups are displaced from the C4‐plane, which we propose maximises U−C4 orbital overlap. DFT calculations identify two quasi‐degenerate U−C4 π‐bonds utilising the ψ2 and ψ3 molecular orbitals of the C4‐unit, but the potential δ‐bond using the ψ4 orbital is vacant. [ABSTRACT FROM AUTHOR]

Ruthenocene-based PCPtBu pincer ligands were used to synthesize novel pincer palladium chloride RcF[PCPtBu]PdCl (2a) and two novel palladium tetrahydroborates RcF[PCPtBu]Pd(BH4) (3a) and Rc*[PCPtBu]Pd(BH4) (3b), where RcF[PCPtBu] = κ3-{2,5-(tBu2PCH2)2-C5H2}Ru(CpF) (CpF = C5Me4CF3), and Rc*[PCPtBu] = κ3-{2,5-(tBu2PCH2)2C5H2}Ru(Cp*) (Cp* = C5Me5). These coordination compounds were characterized by X-ray, NMR and FTIR techniques. Analysis of the X-ray data shows that an increase of the steric bulk of non-metalated cyclopentadienyl ring in 3a and 3b relative to non-substituted Rc[PCPtBu]Pd(BH4) analogue (3c; where Rc[PCPtBu] = κ3-{2,5-(tBu2PCH2)2C5H2}Ru(Cp), Cp = C5H5) pushes palladium atom from the middle plane of the metalated Cp ring in the direction opposite to the ruthenium atom. This displacement increases in the order 3c < 3b < 3a following the order of the Cp-ring steric volume increase. The analysis of both X-ray and IR data suggests that BH4 ligand in both palladium tetrahydroborates 3a and 3b has the mixed coordination mode η1,2. The strength of the BH4 bond with palladium atom increases in the order Rc[PCPtBu]Pd(BH4) < Rc*[PCPtBu]Pd(BH4) < RcF[PCPtBu]Pd(BH4) that appears to be affected by both steric and electronic properties of the ruthenocene moiety.

The hydride donating ability (HDA), determined as Gibbs free energy (ΔG° H − ) for the reaction of H − dissociation, was assessed via the DFT/M06/6-311++G (d,p) calculations for 90 tetracoordinated borohydrides Li [L 3 B-H] taking into account the solvent effects via the optimization in MeCN and CH 2 Cl 2 under SMD model. Obtained this way, the HDA MeCN values vary from 118.2 to 13.4 kcal/mol and correlate well with the Lewis acidity parameters (AN, HA and FA) of parent trigonal boranes (L 3 B). These data show numerically how the variation of the substituents at the boron atom allows the fine-tuning the B–H bond reactivity (reduction power) in the reactions involving hydride transfer as well as the selectivity of the reduction processes. The analysis of the data obtained shows that by varying the number of substituents and their nature, it is possible not only to change the properties of neutral trisubstituted boranes from highly electrophilic (represented by halogenide- and pseudohalogenide-boranes) to highly nucleophilic (exemplified by alkoxy-an amidoboranes), but also to repolarize the boron-bound hydrogen and make the proton transfer process more favourable than the hydride transfer. [ABSTRACT FROM AUTHOR]

Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. The rare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. [ABSTRACT FROM AUTHOR]

The reaction mechanism for the step-wise alcoholysis of BH 4 − , THF·BH 3 , Me 2 NH·BH 3 and BH 3 by ROH [ROH = CH 3 OH, CF 3 CH 2 OH (TFE) and (CF 3 ) 2 CHOH (HFIP)] was studied computationally. The calculations were performed in gas phase at the DFT/M06/6-311++G(d,p) theory level taking into account non-specific solvent effects by SMD approach. The dihydrogen bonded complexes BH⋯HOR are the intermediates of this cascade borohydride alcoholysis, which set the proper orientation of the reactants molecules and direct their further activation. The consecutive introduction of RO groups instead of hydride ligands in [(RO) n BH (4−n) ] − (n = 0–3) decreases the dihydrogen bond strength due to the stabilization of borohydride HOMO orbital and the decrease of molecular electrostatic potential. Nevertheless the B H bond polarization and thermodynamic hydricity (hydride donor ability) increase with substitution, leading to the decrease of the reaction barrier. The H H bond formation can be considered as a result of concerted proton and hydride transfer in transition state. For BH 4 − alcoholysis the highest activation barrier was computed for the first reaction step: BH 4 − + HOR → H 2 + [(RO)BH 3 ] − and the reaction is self-accelerating. The proton accepting and hydride donor abilities of neutral 4-coordinate borohydrides X·BH 3 (X = THF, NHMe 2 ) are lower than those of BH 4 − . Accordingly the activation barriers change in the order BH 4 − < THF·BH 3 < Me 2 NH·BH 3 and at any reaction stage they remain higher than the barrier for the reaction of [(RO)BH 3 ] − with the same alcohol. Together with low activation barrier for B X bond dissociation (X = O, N) this suggests the ligand exchange and the switch to the kinetically more favorable [(RO)BH 3 ] − alcoholysis. [ABSTRACT FROM AUTHOR]

Nowadays, among all known borohydrides magnesium borohydride, Mg(BH 4 ) 2 , is the only one that demonstrates a partial reversible hydrogen sorption in moderate conditions. This is a clear reason why composites based on Mg(BH 4 ) 2 are extensively studied fundamentally and are applicable as hydrogen storage materials. The review summarizes the main challenges still present for Mg(BH 4 ) 2 that are decomposition and formation providing for the practical use of hydrogen mobility. Some technological approaches to the development of nanocomposites based on Mg(BH 4 ) 2 are considered and discussed. Profound conclusions and future application of nanocomposites in fuel cells and secondary batteries is the final item of the proposed work. [ABSTRACT FROM AUTHOR]

Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. The rare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2.

Hydrazine and its derivatives are used as fuels in rocket propellant systems; however, due to high vapor pressure, toxicity, and carcinogenicity, handling of such compounds is extremely hazardous. Hypergolic ionic liquids have shown great promise to become viable replacements for hydrazines as fuels. Borohydride-containing ionic liquids have now been synthesized using a more efficient synthetic pathway that does not require liquid ammonia and halide precursors. Among the eight new compounds, 1-allyl-3-n-butyl-imidazolium borohydride ( 1) and 1, 3-diallylimidazolium borohydride ( 5) exhibit very short ignition-delay times (ID) of 8 and 3 ms, respectively. The hydrolytic stability of borohydride compounds has been greatly improved by attaching long-chain alkyl substituents to the imidazole ring. 1,3-Di-( n-octyl)-imidazolium borohydride ( 3) is a water stable borohydride-containing ionic liquid. 1,3-Di-( n-butyl)-imidazolium borohydride ( 2) is a unique example of a borohydride liquid crystal. These ionic liquids have some unusual advantages, including negligible vapor pressures, good ignition delay (ID) times, and reduced synthetic and storage costs, thereby showing good application potential as environmentally friendly fuels in bipropellant formulations. In addition, they also have potential applications in the form of reducing agents and hydrogen storage materials. [ABSTRACT FROM AUTHOR]

We overview the literature available in the past 10 years relevant to chemical-vapor generation (CVG) of transition metals in analytical atomic spectrometry. We focus attention on chemical and physical parameters facilitating reaction efficiency, and other experimental conditions affecting efficient separation and transportation of the volatile species generated. We discuss the overall efficiency of the process and the susceptibility to interferences in the liquid and gaseous phases with respect to the two-step mechanism of the generation of volatile species and the chemical nature of analyte vapors. We highlight the role of reaction enhancers, such as complexing reagents, surfactants, dispersed metals and ionic liquids. Finally, we give examples of analytical figures of merit and analytical applications of CVG with different methods of atomic spectrometry. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gas chromatography is suitable for speciation of Hg, Pb, Sn, Se, As, etc. [•] In GC methods, tetraalkylborates are employed for derivatization of analytes. [•] Alkylation reactions are fast, convenient and can be performed in aqueous media. [•] Recent applications to environmental, biological and food matrices are reviewed. [ABSTRACT FROM AUTHOR]

Abstract: Borohydride complexes of the rare earths have attracted increasing interest during the last decade. This review aims to cover recent results over this period with respect to the preparation, characterization, structure, and applications in organic chemistry of this family of compounds, including inorganic and organometallic complexes. Special emphasis is made on their use for polymerization catalysis. [ABSTRACT FROM AUTHOR]

Abstract: Addition of tertiary phosphines to Th(BH4)4(Et2O)2 yields the new Lewis base adducts, Th(BH4)4(PMe3)2, Th(BH4)4(PEt3)2, and Th(BH4)4(dmpe)2, where dmpe=1,2-bis(dimethylphosphino)ethane. If one considers the groups to occupy one coordination site, then Th(BH4)4(PEt3)2 adopts a trans-octahedral geometry, and Th(BH4)4(dmpe)2 adopts a trigonal dodecahedral geometry with the dmpe ligands bridging between the “inner” sites. In the PMe3 and PEt3 complexes, all four groups are κ3, whereas in the dmpe complex two of the groups are κ2 and two are κ3. In the dmpe complex, the Th⋯B distances to the κ2 and κ3 groups are 2.91 and 2.69Å, respectively. All of the Lewis base adducts of Th(BH4)4 are volatile and may be sublimed in vacuum. They have been characterized by infrared and 1H, 11B, and 31P NMR spectroscopy. The results show that thorium complexes of unidentate phosphines can be made and are stable enough to isolate and characterize. 31P NMR coordination chemical shifts of thorium phosphine complexes are on the order of 30–45ppm. The compound Th(BH4)4(dmpe)2 is the first thorium complex to contain κ2 groups. [ABSTRACT FROM AUTHOR]

Abstract: The state of knowledge of the mechanisms involved in the chemical generation of volatile species (CHG) arising from aqueous phase reaction of classical hydride forming elements, transition and noble metals with borane complexes (mainly NaBH4), has been critically reviewed in the light of evidences and literature data published in the last fifty years. The mechanisms, which are necessary to describe the reactivity of CHG system, are essentially: (i) the mechanism of hydrolysis of borane complexes, (ii) the mechanism of formation of volatile species, (iii) the mechanism of liquid phase interference and (iv) the mechanism of action of additives. Only the mechanisms (i) and (ii) have reached a good degree of rationalization, whereas more experimental evidences are necessary for the mechanisms (iii) and (iv). A more general reaction model for analytical CHG can be drawn according to the present state of knowledge, which is valid for both classical hydride forming elements and transition and noble metals. It is based on the formation of analyte–borane complex (ABC) intermediates through which takes place the direct, stepwise transfer of hydrogen atoms from boron to analyte substrate ML n , (M is a metal or semi-metal, L is a ligand). By this way the original analyte substrate is stepwise converted to hydrido metal complexes MH x L y , then to the final products (hydride, metal atoms, etc). The clarification of several controversial aspects and the ruling out of wrong concepts, among them the “nascent” hydrogen theory, can been achieved in the light of the present state of knowledge. [Copyright &y& Elsevier]

Abstract: The synthesis and characterization of (Tp t Bu,Me)Yb(BH4)(THF) n (n =0, 3; n =1, 4) complexes are reported. The compounds represent rare examples of lanthanide (II) tetrahydroborate complexes. The X-ray crystal structure of complex 4 has been determined and it shows a monomeric, formally seven coordinate ytterbium center, bearing one κ3 bonded Tp t Bu,Me ligand, a tetrahydroborate ligand and a coordinated THF molecule. The tetrahydroborate ligand binds in a κ3 fashion, via three bridging hydrogen atoms. IR spectroscopy data are consistent with the solid-state structure and the corresponding BD4 analog of 4 shows the expected IR isotope shifts. The 1H NMR spectra of 3 and 4 shows one set of resonances each for the BH4 and the pyrazolylborate ligands indicating dynamic solution behavior. For complex 3, although X-ray quality crystals could not be obtained, the IR and NMR data are consistent with its formulation as the solvent-free analog of complex 4 with κ3-bonded BH4 ligand. [Copyright &y& Elsevier]

A set of standard compounds for x-ray photoelectron spectroscopy (XPS): KBH4, NaBPh4, and KBF4 has been identified. Literature data on XPS for salts of the anions $\rm{BH_4^-}$, $\rm{BF_4^-}$, and $\rm{BPh_4^-}$, the donor-acceptor complexes LBF3, and also their related compounds was analyzed with a view toward the validity of the data. [ABSTRACT FROM AUTHOR]

Abstract: The direct synthesis of Li[BH4] and Li[B11D4] from the corresponding elements at T =700°C and p(H2) (or p(D2))=150bar is demonstrated. The chemical inertness of boron is thought to prevent its reaction with lithium and hydrogen to LiBH4 at lower temperatures. We show, however, that the reaction kinetics can be enforced by a LiB3-like alloy and a Li7B6 intermetallic compound, which are formed in inert argon atmosphere at 330 and 450°C, respectively. The synthesis is performed by exposing the Li–B mixtures to a defined hydrogen pressure in a high pressure stainless steel vessel and the hydrogen adsorption is monitored by the pressure decrease. The product is identified by X-ray powder diffraction. [Copyright &y& Elsevier]

Abstract: We report on the application of a commercially available mercury analyzer, which is based on vapour generation of Hg0 by NaBH4 reduction and atomic absorption detection, to the quantification and characterization of –SH groups and its application to wine samples. The behaviour of Hg(II) and thiol–Hg(II) (RS–Hg) complexes at nanomolar level (RS= l-cysteine, dl-penicillamine, N-acetyl penicillamine, glutathione, cysteinylglycine, homocysteine) has been studied following their reduction with alkaline NaBH4 to give Hg0. In the absence of thiol–Hg(II) is quantitatively converted to Hg0 by stoichiometric amount of NaBH4 (reaction ratio 1/4mole NaBH4/mole Hg), while the complete reduction of Hg(II)–thiol complexes to Hg0 requires molar excess of NaBH4 up to six orders of magnitude, depending on the type of complex and on the pK a of the thiolic group. Under an appropriate excess of reductant, Hg(II) and its thiol complexes are not distinguishable giving the same response. These properties allow the discrimination of Hg(II) from Hg(II)–thiol complexes without any preliminary separation and the quantification of thiol groups. Instrumental detection limits are as low as 2.5pg, permitting sample dilution, therefore, minimizing the risk of possible interferences occurring with complex real matrices. The method has been applied to quantification of thiol groups in wine samples. Comparison with results obtained by HPLC coupled to atomic fluorescence detection confirmed the promising potentialities of the method. [Copyright &y& Elsevier]

Abstract: He I and He II PE spectra of Ti(BH4)3 are reported and assigned by reference to density functional calculations on the molecule and cation. The performance of different functionals in predicting the first vertical ionization energy is assessed. Calculations based on hybrid functionals are found to give ionisation energies closer to the experimental value than those using pure density functionals. The accuracy of the ΔSCF method and time dependent density functional theory in calculating higher vertical ionization energies is also examined. [Copyright &y& Elsevier]

The effect of mM concentrations of K3[Fe(CN)6], Fe(III), Mo(VI), KSCN and KMnO4 on the generation of BiH3 by the reaction of 0.2–10 μg ml−1 Bi(III) with 0.2 M tetrahydroborate(III) at 1 M acidity (HCl or HNO3) was investigated. Chemical vapour generation (CVG) of BiH3 was investigated by atomic absorption spectrometry using a continuous flow reaction system (CF–CVG–AAS) and different mixing sequences and reagent reaction times. Gas chromatography–mass spectrometry (GC–MS) was employed in batch generation experiments with NaBD4. In the absence of additives, the formation of Bi0 at high concentrations of Bi(III) caused rollover of calibration curves and limited the linear range to less than 1 μg ml−1 Bi(III). In the presence of additives, the formation of Bi0 was not observed and the linear range was increased to 5 μg ml−1 of Bi(III) while rollover was completely removed. GC–MS experiments indicated that the presence of additives did not affect the direct transfer of H from boron to bismuth. Experiments with CF–CVG–AAS and different mixing sequences and reagent reaction times suggest that additives act by preventing the formation of Bi0 through the formation of reaction intermediates which evolve towards the formation of BiH3 at elevated Bi(III)/NaBH4 ratios. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ruthenocene-based PCPtBu pincer ligands were used to synthesize novel pincer palladium chloride RcF[PCPtBu]PdCl (2a) and two novel palladium tetrahydroborates RcF[PCPtBu]Pd(BH4) (3a) and Rc*[PCPtBu]Pd(BH4) (3b), where RcF[PCPtBu] = κ3-{2,5-(tBu2PCH2)2-C5H2}Ru(CpF) (CpF = C5Me4CF3), and Rc*[PCPtBu] = κ3-{2,5-(tBu2PCH2)2C5H2}Ru(Cp*) (Cp* = C5Me5). These coordination compounds were characterized by X-ray, NMR and FTIR techniques. Analysis of the X-ray data shows that an increase of the steric bulk of non-metalated cyclopentadienyl ring in 3a and 3b relative to non-substituted Rc[PCPtBu]Pd(BH4) analogue (3c; where Rc[PCPtBu] = κ3-{2,5-(tBu2PCH2)2C5H2}Ru(Cp), Cp = C5H5) pushes palladium atom from the middle plane of the metalated Cp ring in the direction opposite to the ruthenium atom. This displacement increases in the order 3c < 3b < 3a following the order of the Cp-ring steric volume increase. The analysis of both X-ray and IR data suggests that BH4 ligand in both palladium tetrahydroborates 3a and 3b has the mixed coordination mode η1,2. The strength of the BH4 bond with palladium atom increases in the order Rc[PCPtBu]Pd(BH4) < Rc*[PCPtBu]Pd(BH4) < RcF[PCPtBu]Pd(BH4) that appears to be affected by both steric and electronic properties of the ruthenocene moiety. [ABSTRACT FROM AUTHOR]

Interaction of BuNBH with AlCl at 45-50 °C results in the formation of BH and unstable borane BH, which is converted into a mixture of BH, BH, and BH. This reaction can be used for the preparation of tetraborane(10). [ABSTRACT FROM AUTHOR]