Mechanism of B-H Redistribution during Reduction of Polyborazylene by Hydrazine

Density functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia-borane (H₃B−NH₃, AB ) from polyborazylene (B_xN_xH_x, PBz ) in the presence of hydrazine (H₂N−NH₂, Hz ). Herein, borazine (B₃N₃H₆, Bz ) is used as the simplest relevant model of PBz for the regeneration process. Digestion of Bz using Hz was found to occur by a string of Lewis acid base adduct (between B atoms of Bz and Hz molecule) formation and Hz assisted proton transfer processes. Later, B−H bonds of HB(NHNH₂)₂, the Bz digested product, are redistributed to form hydrazine-borane (H₃B−NH₂NH₂, HzB ) and B(NHNH₂)₃. Redistribution of B−H bonds occurs through hydroboration and concerted proton-hydride transfer. Another B−H redistributed product, B(NHNH₂)₃, produces HzB as a result of proton and hydride transfer from cis-diazene ( Dz ), the oxidized product of Hz in presence of O₂.     

Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.     

Bifunctional Behavior of Unsaturated Intramolecular Phosphane–Borane Frustrated Lewis Pairs Derived from Uncatalyzed 1,4‐Hydrophosphination of a Dienylborane

Three unsaturated C₄‐bridged phospane/borane frustrated Lewis pairs (P/B FLPs) are prepared by uncatalyzed hydrophosphination of a dienylborane. The systems are bifunctional. Consequently, two examples undergo clean hydroboration reactions with HB(C₆F₅)₂ to yield B/B/P systems. The 1,4‐P/B system (C₆F₅)₂B?CH₂CH?CMeCH₂PMes₂ reacts with benzaldehyde initially by allylborane addition, followed by internal P/B FLP addition to the pendant C?C double bond, to yield a bicyclic product. The corresponding reaction of (C₆F₅)₂B?CH₂CH?CMeCH₂PtBu₂ stops at the allylborane/benzaldehyde addition product. The related system (C₆F₅)₂B?CH₂CH?CMeCH₂PPh₂ shows a similar bifunctional reaction pattern, whereby allylborane addition to benzaldehyde is combined with P/B addition to a second aldehyde equivalent to form the eight‐membered heterocyclic 1:2 addition product.     

Hydroboration of the Amino(imino)borane [Me3C(Me3Si)N]B[N(CMe3)]

The formation of four products of the type Me₃C(Me₃Si)N=BH–N(CMe₃)=BR'₂ [BR'₂ = B(CHMeiPr)₂ ( 1 ), B(c‐C₆H₁₁)₂ ( 2 ), B(C₈H₁₄) ( 3 ), B(O₂C₆H₄) ( 4 )] from the iminoborane Me₃C(Me₃Si)N–···B=···N(CMe₃) and the hydroboranes (R'₂BH)₂ is described. Crystal structure analysis reveals the molecule 1 to have an N=B–N=B backbone with two orthogonal N=B bond planes and, hence, no conjugation between the two B–N double bonds.     

Infrared Photodisssociation Spectroscopy of Boron Carbonyl Cation Complexes

The boron carbonyl cation complexes B(CO)₃⁺, B(CO)₄⁺ and B₂(CO)₄⁺ are studied by infrared photodissociation spectroscopy and theoretical calculations. The B(CO)₄⁺ ions are characterized to be very weakly bound complexes involving a B(CO)₃⁺ core ion, which is predicted to have a planar DD_3h structure with the central boron retaining the most favorable 8-electron configuration. The B₂(CO)₄⁺ cation is determined to have a planar D_2h structure involving a B-B one and half bond. The analysis of the B-CO interactions with the EDA-NOCV method indicates that the OC→B σ donation is stronger than the B→CO π back donation in both ions.     

Effects of tris(pentafluorophenyl)borane on the activation of a metal alkyl‐free Ni‐based catalyst in the polymerization of 1,3‐butadiene

The activation of a metal alkyl‐free Ni‐based catalyst with B(C₆F₅)₃ was investigated in the polymerization of 1,3‐butadiene. A catalyst of bis(1,5‐cyclooctadiene)nickel (Ni(COD)₂)/B(C₆F₅)₃ was found to have high catalytic activity and 1,4‐cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight (M_w) of up to 117,000, even in the absence of AlR₃ and MAO. Variations in the mol ratio of B(C₆F₅)₃ to Ni affected catalytic activity, 1,4‐cis stereoregularity, and the M_w of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C₆F₅)₃ to Ni. The use of other borane compounds such as B(C₆H₅)₃, BEt₃, and BF₃ etherate in place of B(C₆F₅)₃ clearly showed the two main functions of B(C₆F₅)₃ in the present catalyst. The high Lewis acidity of B(C₆F₅)₃ enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C₆F₅)₃ suppressed chain transfer reactions, contributing to the production of polybutadiene with a high M_w. Kinetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD)₂. A plot of ?ln (1?X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first‐order kinetics with respect to monomer concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1164–1173, 2004     

Phase stability and mechanical properties of rhenium borides by first‐principles calculations

The phase stability and elastic properties of Re? B system were systematically investigated by use of the density functional theory. The formation enthalpies are negative for Re₃B, Re₇B₃, Re₂B, ReB, Re₂B₃, and ReB₂, indicating that they are thermodynamically stable. Re₇B₃, Re₂B, ReB, Re₂B₃, and ReB₂ are mechanically stable. Combining the study of enthalpy and pressure relationship with the convex hull, it was found that the ground state phases are Re₃B, Re₇B₃, and ReB₂ at zero pressure, in agreement with the experimental observations. At the pressure of 90 GPa, Re₃B, and ReB₂ are the most stable phases. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Theoretical Study on Photoisomerization Mechanisms of Diphenyl-Substituted N,C-Chelate Organoboron Compounds

N,C-chelate organoboron compounds are widely employed as photoresponsive and optoelectronic materials due to their efficient photochromic reactivity. It was found in experiments that two diphenyl-substituted organoboron compounds, namely B(ppy)Ph₂ (ppy=2-phenylpyridyl) and B(iba)Ph₂ (iba=N-isopropylbenzylideneamine), show distinct photochemical reactivity. B(ppy)Ph₂ is inert on irradiation, whereas B(iba)Ph₂ undergoes photoinduced transformations, yielding BN-cyclohepta-1,3,5-triene via a borirane intermediate. In this work, the complete active space self-consistent field and its second-order perturbation (CASPT2//CASSCF) methods were used to investigate the photoinduced reaction mechanisms of B(ppy)Ph₂ and B(iba)Ph₂. The calculations showed that the two compounds isomerize to borirane in the same way by passing a transition state in the S₁ state and a conical intersection between the S₁ and S₀ states. The energy barriers in the S₁ state of 0.54 and 0.26 eV for B(ppy)Ph₂ and B(iba)Ph₂, respectively, were explained by analyzing the charge distributions of minima in S₀ and S₁ states. The results provide helpful insights into the excited-state dynamics of organoboron compounds, which could assist in rational design of boron-based photoresponsive materials.     

Deprotonation of a Hydridoborate Anion

The first deprotonation of a borohydride anion was achieved by treatment of [BH(CN)₃]⁻ with strong non‐nucleophilic bases, which resulted in the formation of alkali‐metal salts of the tricyanoborate dianion B(CN)₃²⁻ in up to 97 % yield and 99.5 % purity. [BH(CN)₃]⁻ is less acidic than (Me₃Si)₂NH but a stronger acid than i Pr₂NH. Less sterically hindered, more nucleophilic bases such as PhLi and MeLi mostly attack a CN group under formation of imine dianions [RC(N)B(CN)₃]²⁻, which can be hydrolyzed to ketones of the [RC(O)B(CN)₃]⁻ type. The boron‐centered nucleophile B(CN)₃²⁻ reacts with CO₂ and CN⁺ reagents to give salts of the [B(CN)₃CO₂]²⁻ dianion and the tetracyanoborate anion [B(CN)₄]⁻, respectively, in excellent yields.     

Quadratic nonlinear optical properties of ruthenium (II)-bipyridine complexes in crystalline powders

Quadratic nonlinear optical properties for the crystalline powders of two types of ruthenium-bipyridine [Ru(bipy)₃] complexes were investigated. The nonlinear optical processes markedly depended on the molecular structures of the ruthenium complexes. Second harmonic generation (SHG) and very weak two-photon emission were observed for the alkylated ruthenium-bipyridine compexes with two long alkyl chains attached via amide bonds (RuC_nB), whereas only two-photon emission was observed for Ru(bipy)₃. The existence of two amide bonds in one bipyridine ligand for RuC_nB complexes most probably enhanced the molecular hyperpolarizability as compared with Ru(bipy)₃. The SHG intensity from RuC_nB complexes increased in the order RuC₁₈B < RuC₁₂B < RuC₁₆B. The order of SHG intensity from RuC_nB was ascribed to the difference in size of each crystalline powder estimated by X-ray diffraction methods.     

Geometry,Vibrational and NMR Spectra of Icosahedral 1-Methylazacloso-dodecaborane

Geometry, vibrational and NMR spectra of the icosahedral aza-closo-dodecaborane MeNB₁₁H₁₁ are calculated by ab initio methods. The results are compared with experimental data. They are in accord with local C_5v symmetry of the cluster unit and local C_3v symmetry of the methyl group. The boron atoms B7–B11 are coupled to B12 by the small constant ¹J (¹¹B, ¹¹B) = 12 Hz.     

Syntheses and Structures of New Rare‐Earth Metal Tetracyanidoborates

Six new rare‐earth metal tetracyanidoborates were prepared and characterized by single‐crystal X‐ray diffraction. Crystals of these salts contain co‐crystallized solvent molecules, such as water, acetone, ethanol, or diethyl ether. In [La(EtOH)₃(H₂O)₂{B(CN)₄}₃] ( 1 ), [La(EtOH)(H₂O)₄{B(CN)₄}₃] · Et₂O ( 2 ), and [Y(EtOH)(H₂O)₄{B(CN)₄}₃] · EtOH ( 6 ) the tetracyanidoborate anions are all or in part bonded to the RE³⁺ ions, whereas in [Pr(H₂O)₉][B(CN)₄]₃ · (CH₃)₂CO ( 3 ), [Er(H₂O)₈][B(CN)₄]₃ · (CH₃)₂CO ( 4 ), and [Lu(EtOH)(H₂O)₇][B(CN)₄]₃ · EtOH · 0.5H₂O ( 5 ) the [B(CN)₄]^– anions are not coordinated to the central metal atoms. Only in 1 , one of the three crystallographically independent [B(CN)₄]^– anions acts as a bridging ligand.     

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory

The C? NO₂ bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C? NO₂ bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO₂ groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol^?1 from experimental ones for CH₂(NO₂)₂ and CH(NO₂)₃, when the diffusion functions are not augmented. For the C(NO₂)₄ molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Coordination Polymer Nanobamboos of {FexIn1−x}‐MIL‐88B: Induced Formation of a Virtual In‐MIL‐88B

A precise fabrication of nanobamboo structures made from hybrid coordination polymers of the type {Fe_xIn_1?x}‐MIL‐88B is demonstrated. The compositions of the hybrid coordination polymer nanobamboos of {Fe_xIn_1?x}‐MIL‐88B (x=0.06, 0.19, or 0.75) are regulated by altering the amount of metal ions used in the reactions. Interestingly, the formation of a virtual In‐MIL‐88B (precise structure, {Fe_0.06In_0.94}‐MIL‐88B), which cannot be created in a typical reaction, is induced by the assistance of a Fe‐MIL‐88B structure. The a and c cell parameters of {Fe_0.06In_0.94}‐MIL‐88B are calculated at 10.95 and 19.86 Å, respectively. These values of {Fe_0.06In_0.94}‐MIL‐88B are larger than those of pure Fe‐MIL‐88B owing to the large ionic size of In³⁺ within the framework.     

Boron-Made N2: Realization of a B≡B Triple Bond in the B2Al3− Cluster

Until now, all B≡B triple bonds have been achieved by adopting two ligands in the L→B≡B←L manner. Herein, we report an alternative route of designing the B≡B bonds based on the assumption that by acquiring two extra electrons, an element with the atomic number Z can have properties similar to those of the element with the atomic number Z+2. Specifically, we show that due to the electron donation from Al to B, the negatively charged B≡B kernel in the B₂Al₃⁻ cluster mimics a triple N≡N bond. Comprehensive computational searches reveal that the global minimum structure of B₂Al₃⁻ exhibits a direct B–B distance of 1.553 Å, and its calculated electron vertical detachment energies are in excellent agreement with the corresponding values of the experimental photoelectron spectrum. Chemical bonding analysis revealed one σ and two π bonds between the two B atoms, thus confirming a classical textbook B≡B triple bond, similar to that of N₂.     

SrPd4B and BaPd4B: New Type of Crystal Structure and Physical Properties

Two new intermetallic alkaline‐earth palladium borides, SrPd₄B and BaPd₄B were synthesised and their physical properties were investigated. The crystal structure of SrPd₄B was solved from powder X‐ray diffraction data: new structure type, space group Pnma, a = 6.0014(1) Å, b = 5.5041(1) Å, c = 11.8723(2) Å, R_I = 0.065, R_P = 0.093. BaPd₄B is isostructural with a = 6.0883(1) Å, b = 5.6066(1) Å, c = 12.0050(2) Å, R_I = 0.062, R_P = 0.097. The relationship of this structure type with the series of derivatives of the CaCu₅ type is discussed. Calculated electronic band structures for palladium, Pd₃B, SrPd₅, SrPd₄B and SrPd₃B are compared. The role of boron and strontium for the electronic properties is discussed in detail. SrPd₄B shows metallic behaviour with a DOS(E_F) ≈? 1.7 eV^–1 · f.u.^–1 at the Fermi level. Magnetic properties, electrical resistivity and specific heat capacity measurements reveal that the two compounds are diamagnetic metallic conductors with low electronic density of states, in agreement, with the electronic structure calculations.     

1,4-dicyanobutene-bridged binuclear rhodium(I) complexes and their catalytic activities

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with dicyano olefins, cis-NCCHCH-CH₂CH₂CN (c-DC1B), rans-NCCHCHCH₂CH₂CN (t-DC1B), trans-NCCH₂CHCHCH₂CN (t-DC2B), and NCCH₂CH₂CH₂CN (DCB) produce the binuclear dicationic rhodium(I) complexes, [(CO)(PPh₃)₂RhNCACNRh-(PPh₃)₂(CO)](ClO₄)₂ (NCACN = c-DC1B 1), t-DC1B (2), t-DC2B (3), DCB (4). Complexes 1 and 2 are catalytically active for the hydrognation of c-DC1B and t-DC1B, respectively, to give DCB, while complex 3 catalyze the isomerization of t-DC2B to give c-DC1B and t-DC1B, and the hydrogenation of t-DC2B to DCB at 100°C.     

Synthesis of some halogenated tetraarylborates

The reactions of 3,4-dichlorophenylmagnesium bromide and 3,5-dichlorophenylmagnesium bromide with B(OEt)₃ and NaBF₄ were studied The corresponding tetraarylborates [(3,4-Cl₂C₆H₃)₄B]NH₄ and [(3,5-Cl₂C₆H₃)₄B]Na were obtained and characterized. The significant influence of the substituents inductive effect on the reaction course was revealed. NaBF₄ was found to be a valuable boron reagent in the synthesis of tetraarylborates containing highly electronegative substituents. The molecular structure of [(3-CF₃C₆H₄)₄B]NH₄ obtained from the reaction of 3-trifluoromethylbromobenzene with NaBF₄ and Mg was determined using X-ray analysis.