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61.
Dr. Andrey Y. Khalimon Prof. Dr. Stanislav K. Ignatov Andrey I. Okhapkin Dipl.‐Ing. Razvan Simionescu Prof. Dr. Lyudmila G. Kuzmina Prof. Dr. Judith A. K. Howard Dr. Georgii I. Nikonov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8573-8590
The reactions of bis(borohydride) complexes [(RN?)Mo(BH4)2(PMe3)2] ( 4 : R=2,6‐Me2C6H3; 5 : R=2,6‐iPr2C6H3) with hydrosilanes afford new silyl hydride derivatives [(RN?)Mo(H)(SiR′3)(PMe3)3] ( 3 : R=Ar, R′3=H2Ph; 8 : R=Ar′, R′3=H2Ph; 9 : R=Ar, R′3=(OEt)3; 10 : R=Ar, R′3=HMePh). These compounds can also be conveniently prepared by reacting [(RN?)Mo(H)(Cl)(PMe3)3] with one equivalent of LiBH4 in the presence of a silane. Complex 3 undergoes intramolecular and intermolecular phosphine exchange, as well as exchange between the silyl ligand and the free silane. Kinetic and DFT studies show that the intermolecular phosphine exchange occurs through the predissociation of a PMe3 group, which, surprisingly, is facilitated by the silane. The intramolecular exchange proceeds through a new non‐Bailar‐twist pathway. The silyl/silane exchange proceeds through an unusual MoVI intermediate, [(ArN?)Mo(H)2(SiH2Ph)2(PMe3)2] ( 19 ). Complex 3 was found to be the catalyst of a variety of hydrosilylation reactions of carbonyl compounds (aldehydes and ketones) and nitriles, as well as of silane alcoholysis. Stoichiometric mechanistic studies of the hydrosilylation of acetone, supported by DFT calculations, suggest the operation of an unexpected mechanism, in that the silyl ligand of compound 3 plays an unusual role as a spectator ligand. The addition of acetone to compound 3 leads to the formation of [trans‐(ArN)Mo(OiPr)(SiH2Ph)(PMe3)2] ( 18 ). This latter species does not undergo the elimination of a Si? O group (which corresponds to the conventional Ojima′s mechanism of hydrosilylation). Rather, complex 18 undergoes unusual reversible β‐CH activation of the isopropoxy ligand. In the hydrosilylation of benzaldehyde, the reaction proceeds through the formation of a new intermediate bis(benzaldehyde) adduct, [(ArN?)Mo(η2‐PhC(O)H)2(PMe3)], which reacts further with hydrosilane through a η1‐silane complex, as studied by DFT calculations. 相似文献
62.
Dr. Laia Vilà‐Nadal Dr. Scott G. Mitchell Dr. Stanislav Markov Dr. Christoph Busche Dr. Vihar Georgiev Prof. Asen Asenov Prof. Leroy Cronin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16502-16511
We explore the concept that the incorporation of polyoxometalates (POMs) into complementary metal oxide semiconductor (CMOS) technologies could offer a fundamentally better way to design and engineer new types of data storage devices, due to the enhanced electronic complementarity with SiO2, high redox potentials, and multiple redox states accessible to polyoxometalate clusters. To explore this we constructed a custom‐built simulation domain bridge. Connecting DFT, for the quantum mechanical modelling part, and mesoscopic device modelling, confirms the theoretical basis for the proposed advantages of POMs in non‐volatile molecular memories (NVMM) or flash‐RAM. 相似文献
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65.
Leonardo M. da Costa Stanislav R. Stoyanov Raimundo N. Damasceno José Walkimar de M. Carneiro 《International journal of quantum chemistry》2013,113(24):2621-2628
Density Functional Theory (UB3LYP/6‐311++G(d,p)) calculations of the affinity of the pentaaqua nickel(II) complex for a set of phosphoryl [O?P(H)(CH3)(PhR)], imino [HN?C(CH3)(PhR)], thiocarbonyl [S?C(CH3)(PhR)] and carbonyl [O?C(CH3)(PhR)] ligands were performed, where R?NH2, OCH3, OH, CH3, H, Cl, CN, and NO2 is a substituent at the para‐position of a phenyl ring.The affinity of the pentaaqua nickel(II) complex for these ligands was analized and quantified in terms of interaction enthalpy (ΔH), Gibbs free energy (ΔG298), geometric and electronic parameters of the resultant octahedral complexes. The ΔH and ΔG298 results show that the ligand coordination strength increases in the following order: carbonyl < thiocarbonyl < imino < phosphoryl. This coordination strength order is also observed in the analysis of the metal‐ligand distances and charges on the ligand atom that interacts with the Ni(II) cation. The electronic character of the substituent R is the main parameter that affects the strength of the metal‐ligand coordination. Ligands containing electron‐donating groups (NH2, OCH3, OH) have more exothermic ΔH and ΔG298 than ligands with electron‐withdrawing groups (Cl, CN, NO2). The metal‐ligand interaction decomposed by means of the energy decomposition analysis (EDA) method shows that the electronic character of the ligand modulates all the components of the metal‐ligand interaction. The absolute softness of the free ligands is correlated with the covalent contribution to the instantaneous interaction energy calculated using the EDA method. © 2013 Wiley Periodicals, Inc. 相似文献
66.
The fluorescent reagent 4,5-diaminofluorescein (DAF-2) has been widely used for specific and quantitative measurements of nitric oxide (NO) in biological tissues. Recently it was reported that dehydroascorbic acid (DHA) and ascorbic acid (AA) interfere with the measurement of NO using DAF-2. A new method of assaying NO using DAF-2 eliminates these interferences; when frozen on dry ice, the NO in the original solution still diffuses and can react with an adjacent frozen block of DAF-2, but the confounding compounds such as DHA do not. Thus, placing the microliter-volume frozen blocks of solutions containing NO and the solutions of DAF-2 adjacent to each other for 30 min results in the concentration dependent formation of fluorescent product (DAF-2T) from the reaction of NO with DAF-2. The product has been characterized and the method validated using both fluorescence spectroscopy and capillary electrophoresis with laser induced fluorescence detection. With this approach, the presence of DHA and AA does not interfere with NO measurements, and product formation is inhibited in the presence of NO scavengers added to either of the solutions before freezing. The contactless DAF-2 method successfully assays NO in nitric oxide synthase-positive vertebrate and invertebrate tissues. This method allows nondestructive NO detection in biological samples that can subsequently be used for morphological and/or biochemical studies. 相似文献
67.
Cline Schneider Frdric Doucet Stanislav Strekopytov Christopher Exley 《Polyhedron》2004,23(18):3185-3191
Hydroxyaluminosilicates (HAS) are critical secondary mineral phases in the biogeochemical cycle of aluminium. They are formed from the reaction of silicic acid (Si(OH)4) with an aluminium hydroxide template and act as a geochemical control of the biological availability of Al. There are two main forms of HAS which we have called HASA and HASB and which of these will predominate will depend upon the Si(OH)4 to Al ratio in any one environment. In all but the most heavily weathered environments or those undergoing a progressive acidification Si(OH)4 will be present in significant excess to Al and HASB will be the dominant secondary mineral phase. We have tried to determine the solubility of HASB(s) so that its contribution to Al solubility control might be compared with other secondary minerals such as Al(OH)3(gibbsite). In preliminary experiments, the dissolution of HASB(s) was found to be non-congruent with almost no Al being released during 18 months ageing. We then demonstrated that HASB(s) was significantly less soluble than Al(OH)3(s) prepared under identical experimental conditions. We have used this information to describe a solubility expression for HASB(s) at a predefined quasi-equibrium and to calculate a solubility constant.
K*Al2Si2O5(OH)4=[Al2O4+][SiO2]2[OH-]4