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1.
The gas‐phase acidity of a series of amine–borane complexes has been investigated through the use of electrospray mass spectrometry (ESI‐MS), with the application of the extended Cooks kinetic method, and high‐level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH3 to give amine–borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH3 leads to a substantial increase (from 167 to 195 kJ mol?1) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude. Interestingly, this increase in acidity is almost twice as large as that observed for the corresponding phosphine–borane analogues. The agreement between the experimental and the G4‐based calculated values is excellent. The analysis of the electron‐density rearrangements of the amine and the borane moieties indicates that the dative bond is significantly stronger in the N‐deprotonated anion than in the corresponding neutral amine–borane complex, because the deprotonated amine is a much better electron donor than the neutral amine. On the top of that, the newly created lone pair on the nitrogen atom in the deprotonated species, conjugates with the BN bonding pair. The dispersion of the extra electron density into the BH3 group also contributes to the increased stability of the deprotonated species.  相似文献   

2.
Mg and Ca β‐diketiminato silylamides [HC{(Me)CN(2,6‐iPr2C6H3)}2M(THF)n{N(SiMe3)2}] (M=Mg, n=0; M=Ca, n=1) were studied as precatalysts for the dehydrogenation/dehydrocoupling of secondary amine–boranes R2HNBH3. By reaction with equimolar quantities of amine–boranes, the corresponding amidoborane derivatives are formed, which further react to yield dehydrogenation products such as the cyclic dimer [BH2?NMe2]2. DFT was used here to explore the mechanistic alternatives proposed on the basis of the experimental findings for both Mg and Ca amidoboranes. The influence of the steric demand of amine–boranes on the course of the reaction was examined by performing calculations on the dehydrogenation of dimethylamine–borane (DMAB), pyrrolidine–borane (PB), and diisopropylamine–borane. In spite of the analogies in the catalytic activity of Mg‐ and Ca‐based complexes in the dehydrocoupling of amine–boranes, our theoretical analysis confirmed the experimentally observed lower reactivity of Ca complexes. Differences in catalytic activity of Mg‐ and Ca‐based complexes were examined and rationalized. As a consequence of the increase in ionic radius on going from Mg2+ to Ca2+, the dehydrogenation mechanism changes and formation of a key metal hydride intermediate becomes inaccessible. Dimerization is likely to occur off‐metal in solution for DMAB and PB, whereas steric hindrance of iPr2NHBH3 hampers formation of the cyclic dimer. The reported results are of particular interest because, although amine–borane dehydrogenation is now well established, mechanistic insight is still lacking for many systems.  相似文献   

3.
The μ‐amino–borane complexes [Rh2(LR)2(μ‐H)(μ‐H2B=NHR′)][BArF4] (LR=R2P(CH2)3PR2; R=Ph, iPr; R′=H, Me) form by addition of H3B?NMeR′H2 to [Rh(LR)(η6‐C6H5F)][BArF4]. DFT calculations demonstrate that the amino–borane interacts with the Rh centers through strong Rh‐H and Rh‐B interactions. Mechanistic investigations show that these dimers can form by a boronium‐mediated route, and are pre‐catalysts for amine‐borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysis.  相似文献   

4.
The recently synthesized rhodium complex [Rh{P(C5H9)22‐C5H7)}(Me2HNBH3)2]BArF4 ( 2 ), which incorporates two amine‐boranes coordinated to the rhodium center with two different binding modes, namely η1 and η2, has been used to probe whether bis(σ‐amine‐borane) motifs are important in determining the general course of amine‐boranes dehydrocoupling reactions. DFT calculations have been carried out to explore mechanistic alternatives that ultimately lead to the formation of the amine‐borane cyclic dimer [BH2NMe2]2 ( A ) by hydrogen elimination. Sequential concerted, on‐ or off‐metal, intramolecular dehydrogenations provide two coordinated amine‐borane molecules. Subsequent dimerization is likely to occur off the metal in solution. In spite of the computationally confirmed presence of a BH???NH hydrogen bond between amine‐borane ligands, neither a simple intermolecular route for dehydrocoupling of complex 2 is operating, nor seems [Rh{P(C5H9)22‐C5H7)} B ]+ to be important for the whole dehydrocoupling process.  相似文献   

5.
Amino acids have been found to form good redox initiator systems with halogens (Cl2 and Br2), KBrO3, KMnO4, and Fe(NH4)(SO4)2. The three systems, viz., glycine–Cl2, taurine–Cl2, and sulfamic acid–Cl2 incorporate amine, carboxy (or sulfoxy), chlorine, and hydroxy endgroups in the resulting polymers, the monomer investigated being mainly methyl methacrylate. On the basis of endgroup results it is suggested that initiation through amino acid radical, chlorine radical and also through some hydroxyl radicals takes place. The probable termination mechanism is discussed.  相似文献   

6.
{Rh(xantphos)}‐based phosphido dimers form by P C activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B⋅NMeH2 and dimeric [H2BNMe2]2 from H3B⋅NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization.  相似文献   

7.
{Rh(xantphos)}‐based phosphido dimers form by P? C activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B?NMeH2 and dimeric [H2BNMe2]2 from H3B?NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization.  相似文献   

8.
Bis‐trimethylamine‐ethynyl‐di‐bis(trifluoromethyl)borane [Me3N(CF3)2BCCB(CF3)2NMe3] ( 1 ) has been prepared from trimethylamine‐ethynyl‐bis(trifluoromethyl)borane, [HCCB(CF3)2NMe3], and dimethylamino‐bis(trifluoromethyl)borane, (CF3)2BNMe2. The structure of 1 has been determined by x‐ray crystallography. In the solid state the molecule possesses crystallographic Ci symmetry. The acetylenic attachment to the boron atom is characterized by a short B–C bond length of 1.565(4) Å and an essentially linear B–C–C′ bond angle of 178.1(4)°.  相似文献   

9.
A series of novel the semicarbazone derivatives of calix[4]arene have been synthesized and then immobilized onto amino functionalized magnetic nanoparticles. Magnetic Fe3O4 nanoparticles were prepared by the chemical co-precipitation of Fe(III) and Fe(II) ions and the nanoparticles were modified directly by 3-aminopropyltriethoxy silane (APTES) to introduce reactive amine groups onto the particles’ surface. The characterization of the prepared compounds was made by FT-IR, elemental analysis, TGA/DTG and NMR techniques. The sorption properties of the new calix[4]arene based magnetic sorbents toward Cr(VI) ion were also studied. The results showed that the prepared magnetic nanoparticles were effective sorbents for the removal of Cr(VI) ion. Also, Langmuir and Freundlich isotherm models were applied for Cr(VI) ion sorption by using MN-C2 and it was found that the experimental data confirmed to Langmiur isotherm model.  相似文献   

10.
The combination of triazole/gold (TA‐Au) and Cu(OTf)2 is identified as the optimal catalytic system for promoting intramolecular hydroboration for the synthesis of a six‐membered cyclic amine–borane. Excellent yields (up to 95 %) and regioselectivities (5‐exo vs. 6‐endo) were achieved through catalyst control and sequential dilution. Good functional‐group tolerance was attained, thus allowing the preparation of highly functionalized cyclic amine–borane substrates, which could not be achieved using other methods. Deuterium‐labeling studies support the involvement of a hydride addition to a gold‐activated alkyne with subsequent C?B bond formation.  相似文献   

11.
The nitrogen and iron(III) co-doped TiO2 (N–Fe–TiO2) samples were synthesized via modified sol–gel method by using alkyl amine as both nitrogen source and pore directing agent. Morphologies and properties of the co-doped TiO2 samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy, UV–Vis spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results showed anatase phase mixed with rutile structure as well as hydroxyl and amine functional groups. The presence of Fe3+ in N–Fe–TiO2 sample was detected at g value of 2.00. In addition, the prepared samples were photocatalytically active for methyl orange degradation under UV light irradiation, but not under visible light.  相似文献   

12.
The relative stability of the radicals that can be produced from amine–boranes and phosphine–boranes is investigated at the G3‐RAD level of theory. Aminyl ([RNH].:BH3) and phosphinyl ([RPH].:BH3) radicals are systematically more stable than the boryl analogues, [RNH2]:BH2. and [RPH2]:BH2.. Despite similar stability trends for [RNH].:BH3 and [RPH].:BH3 radicals with respect to boryl radicals, there are significant dissimilarities between amine– and phosphine–boranes. The homolytic bond dissociation energy of the N?H bond decreases upon association of the amines with BH3, whereas that of the P?H bond for phosphines increases. The stabilization of the free amine is much smaller than that of the corresponding aminyl radical, whereas for phosphines this is the other way around. The homolytic bond dissociation energy of the B?H bond of borane decreases upon complexation with both amines and phosphines.  相似文献   

13.
A synthetic route to enantiomerically pure (1R,2S)‐1‐phenylphospholane‐2‐carboxylic acid ( 1 ), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation–carboxylation of the 1‐phenylphospholane borane complex 3 by using sBuLi/1,2‐dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine‐coordinated α‐phosphinoalkyllithium borane complex 4 , was investigated by employing lithiodestannylation–carboxylation of both diastereomers of the 1‐phenyl‐2‐trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at ?100 °C. The key intermediate, the DPE‐coordinated trans‐1‐phenyl‐2‐phospholanyllithium borane complex 9 , was isolated, and the structure was identified by X‐ray crystal structure analysis. This is the first X‐ray crystal structure determined for an α‐monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li? C bond (2.170 Å) has been confirmed. Moreover, 1H–7Li HOESY and 6Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9 , its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at ?100 °C. Finally, 1 was used as a chiral ligand in a palladium‐catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.  相似文献   

14.
Nickel (Ni) nanoparticles were immobilized on the surface of magnetic MgAl layered double hydroxide intercalated 10-molybdo-2-vanadophosphate (Fe–MgAl/Mo10V2–Ni) for the first time. The presence of Ni nanoparticles onthe high-surface area Fe–MgAl LDH structure in the presence of Mo10V2 makes this catalyst an ideal option in terms of efficiency and selectivity for Heck coupling reaction. Synergic effects of Mo10V2 and Ni were investigated by an electrochemical technique. Increasing of the ECSA of the catalyst compared to Fe–Mg–Al–Ni leads to enhancement of the catalytic activity and proves the synergic effect. A new catalytic mechanism was introduced for this kind of reaction. The resulting structure and its catalytic behavior were characterized by FT-IR, XRD, ICP-AES, TEM, SEM, EDX, EBSD, XPS, BET, VSM, CV, LSV and zeta potential analyses. More importantly, Fe–MgAl/Mo10V2–Ni can easily be separated from the reaction mixture using an external magnet and reused for at least four successive runs without any substantial reduction in its catalytic activity.  相似文献   

15.
The Lewis acidities of a series of [n]magnesocenophanes ( 1 a – d ) have been investigated computationally and found to be a function of the tilt of the cyclopentadienyl moieties. Their catalytic abilities in amine borane dehydrogenation/dehydrocoupling reactions have been probed, and C[1]magnesocenophane ( 1 a ) has been shown to effectively catalyze the dehydrogenation/dehydrocoupling of dimethylamine borane ( 2 a ) and diisopropylamine borane ( 2 b ) under ambient conditions. Furthermore, the mechanism of the reaction with 2 a has been investigated experimentally and computationally, and the results imply a ligand-assisted mechanism involving stepwise proton and hydride transfer, with dimethylaminoborane as the key intermediate.  相似文献   

16.
Fe–TiO2 nanoparticles with Fe concentration from 0.24 to 5 wt % were synthesized in a Al2O3 matrix through multiple impregnations from organic solutions of Ti n-butoxide and Fe acetylacetonate. Microstructure, morphology and magnetic properties of the composites were studied using X-ray analysis, transmission electron microscopy, energy-dispersive analysis, Mössbauer spectroscopy and magnetic susceptibility. It was shown that the deposition of the solution with low concentration of Ti n-butoxide leads to the formation of mostly extensive Fe–TiO2 films with a small fraction of individual Fe–TiO2 nanoparticles. On the contrary, the increase of Ti n-butoxide concentration results in the formation of a great number of individual Fe–TiO2 nanoparticles on Al2O3. The size of these particles increases from 2–3 nm to 5–8 nm with the increase of Fe content in the samples from 0.24 to 1.0 (wt %). Mössbauer spectroscopy revealed two types of magnetic ions. The first type of paramagnetic Fe3+ demonstrate spin–lattice relaxation properties while another one substitutes Ti4+ in the TiO2 structure thus forming Fe–TiO2 stabilized particles in the matrix. According to the magnetic data antiferromagnetic and ferromagnetic types of exchange spin coupling occur in Fe–TiO2/Al2O3 composites. The increase of Fe concentration in the composites from 1 to 5 wt % results in the narrowing of the TiO2 band gap from 3.2 to 2.7 eV and shifting the absorption edge in visual spectrum from 350–400 to 450–500 nm.  相似文献   

17.
N-Heterocyclic carbene (NHC)-stabilized copper nanoparticles (NPs) were synthesized from an NHC–borane adduct and mesitylcopper(I) under thermal conditions (refluxing toluene for 2.5 h). NPs with a size distribution of 11.6±1.8 nm were obtained. The interaction between Cu NPs and NHC ligands was probed by X-ray photoelectron spectroscopy, which showed covalent binding of the NHC to the surface of the NPs. Mechanistic studies suggested that NHC–borane plays two roles: contributing to the reduction of [CuMes]2 to release Cu0 species and providing NHC ligands to stabilize the copper NPs.  相似文献   

18.
Polystyrene‐g‐boramine random copolymers are dihydrogen reservoirs with tunable dehydrogenation temperatures, which can be adjusted by selecting the boramine content in the copolymers. They display a unique dihydrogen thermal release profile, which is a direct consequence of the insertion of the amine–boranes in a polymeric scaffold, and not from a direct modification of the electronics or sterics of the amine–borane function. Finally, the mixture of polystyrene‐g‐boramines with conventional NH3‐BH3 (borazane) allows for a direct access to organic/inorganic hybrid dihydrogen reservoirs with a maximal H2 loading of 8 wt %. These exhibit a dehydrogenation temperature lower than that of either the borazane or the polystyrene‐g‐boramines taken separately.  相似文献   

19.
This study was focused on the photocatalytic activity of polyaniline (Pani)/iron doped titanium dioxide (Fe–TiO2) composites for the degradation of methylene blue as a model dye. TiO2 nanoparticles were doped with iron ions (Fe) using the wet impregnation method and the doped nanoparticles were further combined with Pani via an in situ polymerization method. For comparison purposes, Pani composites were also synthesized in the presence undoped TiO2. The photocatalyst and the composites were characterized by standard analytical techniques such as FTIR, XRD, SEM, EDX and UV–Vis spectroscopies. Fe–TiO2 and its composites exhibited enhanced photocatalytic activity under ultraviolet light irradiation. Improved photocatalytic activity of Fe–TiO2 was attributed to the dopant Fe ions hindering the recombination of the photoinduced charge carriers. Pani/Fe–TiO2 composite with 30?wt.% of TiO2 nanoparticles achieved 28% dye removal and the discoloration rate of methylene blue for the sample was 0.0025?min?1. FTIR, XRD, SEM, EDX and UV–Vis spectroscopies supported the idea that Fe ions integrated into TiO2 crystal structure and Pani composites were successfully synthesized in the presence of the photocatalyst nanoparticles. The novelty of this study was to investigate the photocatalytic activity of Pani composites, containing iron doped TiO2 and to compare their results with that of Pani/TiO2.  相似文献   

20.
A selective preparation and the formation mechanism of hexagonal and cubic CoO nanoparticles from the reaction of [Co(acac)2] (acac=acetylacetonate) and amine have been investigated. CoO nanoparticles with a hexagonal pyramidal shape were yielded under decomposition conditions with amine. Importantly, the addition of water altered the final phase to cubic and comprehensively changed the reaction mechanism. The average sizes of the hexagonal and cubic CoO nanoparticles could be controlled either by changing the amine concentration or by using different reaction temperatures. Detailed formation mechanisms are proposed on the basis of gas chromatography–mass spectrometry data and color changes of the reaction mixture. The hexagonal CoO phase is obtained through two distinct pathways: solvolysis with C C bond cleavage and direct condensation by amine. On the other hand, the cubic CoO nanoparticles were synthesized by strong nucleophilic attack of hydroxide ions from water and subsequent C C bond breaking. The resulting caboxylate ligand can stabilize a cobalt hydroxide intermediate, leading to the generation of a thermodynamically stable CoO phase.  相似文献   

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