Tuning the [L2Rh···H3B·NR3]+ interaction using phosphine bite angle. Demonstration by the catalytic formation of polyaminoboranes

Efficient catalysts for the dehydrocoupling or dehydropolymerisation of H(3)B·NMe(x)H((3-x)) (x = 1, 2) have been developed by variation of the P-Rh-P angle in {Rh(Ph(2)P(CH(2))(n)PPh(2))}(+) fragments (n = 2-5).     

Ir(PCy3)2(H)2(H2B-NMe2)]+ as a latent source of aminoborane: probing the role of metal in the dehydrocoupling of H3B⋅NMe2H and retrodimerisation of [H2BNMe2]2

The Ir^III fragment {Ir(PCy₃)₂(H)₂}⁺ has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H₃B?NMe₂H ( A ) to ultimately give dimeric aminoborane [H₂BNMe₂]₂ ( D ). Addition of A to [Ir(PCy₃)₂(H)₂(H₂)₂][BAr^F₄] ( 1 ; Ar^F=(C₆H₃(CF₃)₂), gives the amine‐borane complex [Ir(PCy₃)₂(H)₂(H₃B?NMe₂H)][BAr^F₄] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy₃)₂(H)₂(H₂B? NMe₂)][BAr^F₄] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H₂ loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H₂BNMe₂ ? [H₂BNMe₂]₂. Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy₃)₂(H)₂(NCMe)₂][BAr^F₄] ( 6 ) liberating H₂B? NMe₂ ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H₃B?NMe₂BH₂?NMe₂H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a B? N bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C .     

An investigation of the catalytic performance of Fe–Mn/Al2O3 nanocatalyst for light olefins production using RSM method and kinetic study

The Fe–Mn/Al₂O₃ nanocatalysts were manufactured via the sol-gel procedure and were evaluated for Fischer–Tropsch synthesis. The impact of different operational parameters of T, P, and H₂/CO ratio on the catalytic performance for light olefins production has been studied using response surface methodology (RSM). Furthermore, the optimization and modeling of selected responses were also carried out via RSM and historical data design type of DOE; and the best process conditions were found to be T = 365°C, H₂/CO = 1.50, and P = 1.50 bar. The mechanism of CO hydrogenation reaction over the Fe–Mn/Al₂O₃ nanocatalysts was also investigated using the non-linear regression method. It was found that the mechanism of the CO hydrogenation reaction is based on the Eley–Rideal type and the best-fitted equation for this mechanism was found to be −r_CO = KP_COP_H2/1+αP_CO. The obtained value of activation energy (85.20 kJ mol⁻¹) affirmed the absence of internal mass transfer limitations. The physico-chemical properties of the samples were investigated by various techniques of XRD, BET, TPR, TGA, and DSC.     

The kinetic and thermodynamic study of KNiPO4·H2O from DSC and TG data

The DSC and TG data showed the dehydration process occurring over the range of 160?C300?°C. The XRD patterns of the synthesized KNiPO₄·H₂O and the calcined product at 350?°C with exposing in the air over 8?h are indexed as the KNiPO₄·H₂O structure, whereas at 600?°C is indexed as KNiPO₄ structure. Hence, these data confirmed that the water molecule was eliminated from the structure at 300?°C, after that the spontaneously reversible hydration?Crehydration process was observed. The activation energy and pre-exponential factor were calculated by Kissinger, Ozawa, and KAS equations. According to the DSC curves, the enthalpy change (??H) of dehydration process can be calculated and was found to be 100.12?kJ?mol^?1. Besides, we suggested another new method to determine the isokinetic temperature value using spectroscopic data. The surface area of synthesized hydrate and its calcined product at 350?°C with exposing in the air at over 8?h were found to be 21.48 and 134.3?m²?g^?1, respectively. The reversible hydration?Crehydration process was observed, and the surface area of final product at 350?°C (aging time over 8?h) is higher than that of the synthesized compound. This behavior is important to develop alternative desiccant materials or other process based on the rehydration mechanism with increasing the surface area.     

A B3LYP and QTAIM study of a new proton donor for dihydrogen bonds: the case of the C2H5 +···nBeH2 complexes (n = 1 or 2)

B3LYP/6-311++G(d,p) calculations and molecular integrations from the quantum theory of atoms in molecules (QTAIM) were performed for the purposes of studying a new class of dihydrogen-bonded hyperconjugation complexes formed by C₂H₅ ⁺···n(BeH₂), when n = 1 (bimolecular) or n = 2 (trimolecular). Whether bimolecular or trimolecular, when the hyperconjugation on the ethyl cation (C₂H₅ ⁺) is taken into account, this enables the earth alkaline hydride, BeH₂, to interact efficiently with the nonlocalized hydrogen (H⁺) of the C₂H₅ ⁺ . In addition to computation of QTAIM topological parameters, analysis of the infrared harmonic spectrum at the B3LYP/6-311++G(d,p) level of theory revealed the existence of red-shifts on BeH₂, and this effect is explained by means of the atomic charges derived from the ChelpG approach. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural study of complex [Rh(NH3)5(NO2)](NO3)2·H2O, [Rh(NH3)5(NO2)][Pd(NO2)4], and K2[Rh(NH3)(NO2)5]·H2O salts

Compounds [Rh(NH₃)₅(NO₂)](NO₃)₂·H₂O (I) with a = 7.6230(3) Å, b = 7.6230(3) Å, c = 10.3584(4) Å, space group I-42m, Z = 2, d _calc = 2.026 g/cm³, V = 601.93(4) ų, Rh-NH_{3 eq} = 2.074 Å, Rh-NH_{3 ax} (NO₂) = 2.048 Å; [Rh(NH₃)₅(NO₂)][Pd(NO₂)₄] (II) with a = 8.095(3) Å, b = 22.422(8) Å, c = 7.887(3) Å, β = 98.559(17)°, space group Cc, Z = 4, d _calc = 2.461 g/cm³, V = 1415.6(9) ų, Rh-NH_{3 eq} = 2.069 Å, Rh-NH_{3 ax} = 2.090 Å, Rh-NO₂ = 2.002 Å; K₂[Rh(NH₃)(NO₂)₅]·H₂O (III) with a = 7.5177(5) Å, b = 20.9856(15) Å, c = 7.7017(5) Å, space group Cmc2₁, Z = 4, d _calc = 2.439 g/cm³, V = 1215.05(14) ų, Rh-NH_{3 ax} (NO₂) = 2.094 Å, Rh-NO_{2 eq} = 2.030 Å are synthesized and studied using single crystal X-ray diffraction.     

Theoretical study of the interaction mechanism of single-electron halogen bond complexes H3C⋯Br-Y (Y = H, CN, NC, CCH, C2H3)

The characteristics and structures of single-electron halogen bond complexes [H₃C?Br-Y (Y = H, CCH, CN, NC, C₂H₃)] have been investigated by theoretical calculation methods. The geometries were optimized and frequencies calculated at the B3LYP/6-311++G** level. The interaction energies were corrected for basis set superposition error (BSSE) and the wavefunctions obtained by the natural bond orbital (NBO) and atom in molecule (AIM) analyses at the MP2/6-311++G** level. For each H₃C?Br-Y complex, a single-electron Br bond is formed between the unpaired electron of the CH₃ (electron donor) radical and the Br atom of Br-Y (electron acceptor); this kind of single-electron bromine bond also possesses the character of a “three-electron bond”. Due to the formation of the single-electron Br bond, the C-H bonds of the CH₃ radical bend away from the Br-Y moiety and the Br-Y bond elongates, giving red-shifted single-electron Br bond complexes. The effects of substituents, hybridization of the carbon atom, and solvent on the properties of the complexes have been investigated. The strengths of single-electron hydrogen bonds, single-electron halogen bonds and single-electron lithium bonds have been compared. In addition, the single-electron halogen bond system is discussed in the light of the first three criteria for hydrogen bonding proposed by Popelier.     

Dimethylformamide as a convenient CO source for the facile preparation of rhodium-, iridium- or ruthenium-chlorocarbonyl complexes directly from RhCl3·3H2O,IrCl3·3H2O or RuCl3·3H2O

The anionic complexes [RhCl₂(CO)₂]⁻, [IrCl₂(CO)₂]⁻ or [RuCl₃(CO)₂(DMF)]⁻ can be obtained in high yields (up to 85 %) and in less than 60 min by refluxing dimethylformamide solutions of RhCl₃·3H₂O, IrCl₃·3H₂O or RuCl₃·3H₂O. Depending on the metal, the presence of small amounts of water and/or hydro- chloric acid greatly accelerates the reduction step. For rhodium, several intermediates have been trapped which allow us to propose a mechanism for this reaction.     

Crystal structure and catalytic properties of a vanadium complex cis-[VO2(Him-py)(im-py)]2·3H2O

Abstract

The coordination behavior of Him-py (2-(1H-imidazol-2-yl)pyridine) toward vanadium has been explored. The six-coordinate complex, cis-[VO₂(Him-py)(im-py)]₂·3H₂O (1), was synthesized by the coordination reaction of NH₄VO₃ and Him-py in the aqueous methanol solution, which was characterized by single-crystal X-ray technology. It belongs to the monoclinic space group P2₁/n with a?=?8.0756(6), b?=?19.3531(15), c?=?11.4433(8), β?=?106.905(2), V?=?1711.2(2), and Z?=?2. The crystal structure shows that the six-coordinate vanadium is bonded to two cis-oxido ligands and two bidentate ligands, Him-py and im-py. Interestingly, when crystals of 1 were immersed in H₂O₂, a peroxovanadium compound, (H₂im-py)[OV(O₂)₂(Him-py)] (2), was obtained, which crystallizes in the orthorhombic space group Fdd2 with a?=?22.600(2), b?=?22.7259(13), c?=?18.0146(11), V?=?9252.4(12), and Z?=?16, and consists of a seven-coordinate peroxovanadate(V) ion, one Him-py and one H₂im-py ligand. Moreover, we also studied the catalytic activity of 1 in the oxidative bromination of phenol/aniline-like compounds towards mimicking bromoperoxidase reactivity.     

PEG–SO3H as a mild, efficient and green catalytic system for the synthesis of pyrazole derivatives in aqueous medium

A versatile, alternative and environmentally benign strategy for the synthesis of a series of pyrazoles has been successfully performed in water using PEG–SO₃H as an acidic catalyst. The products are obtained in high yield from the one-pot reaction procedure involving dicarbonyl compounds and hydrazines/hydrazides. This new method totally avoids the use of organic acids and toxic or expensive solvents in this reaction. The catalyst is waste-free, easily prepared, and efficiently re-used.     

Studies pertaining to the mechanism of “Pt(PCy3)“ addition. The reaction of MPt(μ-H)(μ-PnPr2)Pt(CO)(PCy3) with Pt(C2H4)2(PCy3)

The reaction of Pt(C₂H₄)₂(PCy₃) with (OC)₄M(μ-H)(μ-PⁿPr₂)Pt(CO)(PCy₃, (1: M  Cr, Mo, W) occurs in a highly specific, kinetically controlled manner to give MPt₂(μ²_MPt-CO)(η²_PtPt-H)(μ²_MPt-PⁿPr₂)(CO)₄ (PCy₃)₂ (5), as the first formed trimer. The trimer 5 (M  Mo, W) isomerizes to give MPt₂(μ²_PtPt-CO) ((μ²_MPtH)(μ²_MPt-PⁿPr₂)(CO)₄)PCy₃)₂ (6) which in turn isomerizes to MPt₂μ²_MPtCO)(μ²_MPt (μ²_PtPt-PⁿPr₂)(CO)₄(PCy₃)₂ (7, as the final isolable product. These results provide a detailed insight into the mechanism of “Pt(PCy₃) addition”, a cluster assembly process.     

Synthesis and characterization of a new transition-metal complex of the Lindqvist polyanion Na[Cu(1, 3-pda)2]3[HNb6O19] · 3H2O

A new transition-metal (TM) complex of the Lindqvist polyanion Na[Cu(1, 3-pda)₂]₃[HNb₆O₁₉] · 3H₂O (1, 3-pda = 1, 3-diaminopropane) has been prepared using pre-prepared TBA₄[H₄Nb₆O₁₉] · 7H₂O as a precursor and characterized by single crystal X-ray diffraction, elemental analyses, IR spectra, and thermogravimetric analysis. Crystal data for the compound: rhombohedral, space group R-3c, a = 14.927(4) Å, b = 14.927(4) Å, c = 36.940(18) Å, γ = 120°, V = 7128(4) ų, Z = 6. The structural unit of the title compound consists of a polyanion [HNb₆O₁₉]^7?, a Na⁺, three [Cu(1, 3-pda)₂]²⁺, and three crystal water molecules. The occupancy of all Cu atoms and water molecules is 0.5. X-ray diffraction indicated that the cations and the polyanion were linked through electrostatic interactions and intermolecular forces.     

On the weak O-H···halogen hydrogen bond: a rotational study of CH3CHClF···H2O

We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1?:?1 adduct of CH(3)CHClF with water. Water prefers to form an O-H···F rather than an O-H···Cl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane-water adduct, where an O-H···Cl link was formed (W. Caminati, S. Melandri, A. Maris and P. Ottaviani, Angew. Chem., Int. Ed., 2006, 45, 2438). The water molecule is linked with an O-H···F bridge to the fluorine atom, with r(F···H(w)) = 2.14 ?, and with two C-H···O contacts to the alkyl hydrogens with r(C(1)-H(1)···O(w)) = 2.75 ? and r(C(2)-H(2)···O(w)) = 2.84 ?, respectively. Besides the rotational constants, the quadrupole coupling constants of the chlorine atom have been determined. In addition, information on the internal dynamics has been obtained.     

Synthesis and structures of zirconium complexes [Et2H2N]+2[ZrCl6]2–, [Me3NCH2Ph]+2[ZrCl6]2–•MeCN, [Ph3PC6H4(CHPh2-4)]+2[ZrCl6]2–•2 MeCN,and [Ph4Sb]+2[ZrCl6]2–

Russian Chemical Bulletin - The complexes [Et2H2N]+2[ZrCl6]2– (1), [Me3NCH2Ph]+2[ZrCl6]2–?MeCN (2), [Ph3PC6H4(CHPh2-4)]+2[ZrCl6]2–?2 MeCN (3), and...     

Theoretical study of dodecahydro-closo-decaborane B10H12, the diprotonated boron cluster B10H 10 2−

The electronic and geometric structures of different isomers of the closo-B₁₀H₁₂ boron cluster have been calculated by the density functional theory method (in the B3LYP/6-311++G**//B3LYP/6-31G* approximation). The compound is considered to be the diprotonated (H*) analogue of the well-studied B₁₀H ₁₀ ^2? anion and serves as a model system. The increase in the relative energies of isomers and the preferred location of the extra H* protons near the opposite B(1) and B(10) “poles” are consistent with the charge separation (in the framework of the Mulliken population analysis) between B(1) and B(10). The reactions of migration of one or simultaneously two H* protons in B₁₀H₁₂ over the boron polyhedron have been considered, and the corresponding energies of elementary events E and activation barriers h have been estimated. The elementary events have been predicted in which both H* protons simultaneously move along the trajectories near the opposite B(1) and B(10) poles of the B₁₀H ₁₀ ^2? polyhedron with the same or opposite changes in the angles determining the H* position with respect to the B(1)–B(10) axis. The activation barrier to the “opposite” migration of the H* protons has been assessed to be h ～ 1.2 kcal/mol, whereas for the migration of the H* protons in the same direction, h ～ 1.4 kcal/mol. The H* proton transfer from the position near the B(1) pole to the position near the opposite B(10) pole is hindered, and higher activation barriers on the order of h ～ 13–15 kcal/mol should be overcome for this transfer to occur.     

11B-11B cosy NMR studies of derivatives of the octahydrotriborate anion, [B3H7(X)]− and [B3H6(X)2]−

2-D ¹¹B-¹¹B correlation (COSY) spectra have been obtained on the series of monosubstituted and disubstituted octahydrotriborate anions, [B₃H₇(X)]⁻ (X = Cl, NCS, NCSe, NCBH₃, NCBH₂Cl, NCBPh₃, NCBH₂CN, NCB₃H₇ or CNB₃H₆Cl) and [B₃H₆(Cl)(X)]⁻ (X = Cl, NCS, NCBH₂Cl or NCB₃H₇). All monosubstituted derivatives and [B₃H₆(Cl)₂]⁻ showed a coupling correlation between the substituted and unsubstituted borons. The unsymmetrically disubstituted derivatives showed only one coupling correlation, between the borons carrying the substituents. The absence of other correlations is attributed to relaxation phenomena. The correlations are independent of the solid-state structural type.     

The preparation of a series of ring-linked derivatives of [Fe2(η-C5H5)2(CO)2(μ-CO)2] starting from [Fe2η5,η5-C5H4CH(NMe3)CH(NMe2)C5H4}(CO)2(μ-CO)2]+ salts

The salts [Fe₂η⁵,η⁵-C₅H₄CH{NMe₃)CH(NMe₂)C₅H₄}(CO)₂(μ-CO)₂][X] (X = I or SO₃CF₃) are the synthetic precursors to a wide range of [Fe₂(η-C₅H₅)₂(CO)₂(μ-CO)₂] derivatives in which the two cyclopentadienyl ligands are joined by a two-carbon bridge.     

Synthesis, crystal structure, and thermal analysis of hexahydrogen dodecavanadate of composition [NH3 · H2O]6 · H6[Ca4V12O40] · 6H2O

Dihydrogen dodecavanadate of composition [NH₃ · H₂O]₆ · H₆[Ca₄V₁₂O₄₀] · 6H₂O was synthe-sized and studied by X-ray crystallography and TGA analyses. The crystals are cubic, space group I $\bar 4$ 3m;; unit cell parameters: a = 13.518(2) ?, V = 2470.4(3) ?³, ??_calc = 2.2334 g/cm³, Z = 2.     

Development of a method for the determination of 93Zr and 94Nb in radioactive waste using TEVA® resin

The behaviour of ⁹⁵Zr and ⁹⁵Nb isotopes on TEVA^® resin column was studied. The influence of hydrofluoric, hydrochloric, oxalic and sulphuric acids on the separation and chemical yield of zirconium and niobium was tested. The method is suitable for the separation of ⁹³Zr and ⁹⁴Nb isotopes from hydrofluoric, hydrochloric and sulphuric acid by using different concentrations of the acid for the load or elutes solutions. Samples from reactor and fuel assemblies such as the control-rod connection rod, shielding/absorber parts of fuel rods, neutron in-core measurement channels, pressure vessel basic construction material and internal cladding, core barrel and reactor protection tube unit were analysed.