Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH3)3F- (R = CH3CH2O, CF3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH3)3F- leads to loss of the nucleophile R- and FSi(CH3)3, except in the case of (CH3)3SiNHSi(CH3)3F-, where HF loss is also observed. Ion affinities for FSi(CH3)3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of deltaH(acid) values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R = CH3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH). We use the fluoride affinity of the silanes and the FSi(CH3)3 affinity of the departing nucleophilic anion to assess the feasibility of fluoride-induced desilylation of the silanes examined in this work.     

Theoretical Studies on Substituent Effect of the Reaction of Amide and Formaldehyde

The thermodynamic properties of the reaction of amide and formaldehyde were calculated via B3LYP method when substituents chosen included CH3,CH2CH3,CH2CH2CH3,CH2CH2CH2CH3,CH(CH3)2,CH2CH(CH3)2,CH(CH3)CH2CH3 and C(CH3)3.Based on the optimization of the structures for reactants and products,the thermodynamic functions of all the species for an actual state were obtained.The thermodynamic data and the equilibrium constants were investigated within a temperature range of 300―343.15 K.The calculated results show that the reaction is exothermic and spontaneous.The trends of all thermodynamic properties are consistent with the temperature.The preferential order of the substituent effect is CH2CH(CH3)2CH(CH3)CH2CH3CH2CH2CH2CH3 CH2CH2CH3CH2CH3≈CH(CH3)2C(CH3)3≈CH3.     

Calculation of the Thermodynamic Properties of Silane and Disilane Derivatives and Modeling of the Thermolysis Process

Using the program package from the IVTANTERMO databank, the thermodynamic properties of CH₃SiH₃, CCl₃SiH₃, SiCl₃CH3, SiCl₃SiH₃, SiCl₃CCl₃, and SiCl₃SiCl₃ were calculated and the thermolysis process was studied for CCl₃SiH₃, SiCl₃CCl₃, and SiCl₃SiCl₃.     

Theoretical study of low-lying triplet states of aniline

Multireference complete active space self-consistent-field CASSCF(10,12)/ANO and second-order perturbation theory MS-CASPT2 calculations were performed to determine the vertical low-lying singlet and triplet states of aniline. The sequence of the seven lower lying triplet states is T1(1(3)A'), T2(1(3)A' '), T3(2(3)A'), T4(3(3)A'), T5(2(3)A' '), T6(4(3)A'), and T7(3(3)A' '). The 3(3)A', 4(3)A', and 3(3)A' ' states are assigned as 3s, 3py, and 3pz Rydberg states, respectively, while other states correspond to pi <-- pi excitations. Both the T1 and T2 states are found to be below at the lowest-lying singlet S1 (1(1)A' ') state. Geometry, vibrational modes, and electron distribution of the lowest lying T1 state were determined using UB3LYP calculations. The vertical and adiabatic singlet-triplet energy gaps DeltaE(S0-T1) amount to 3.7 and 3.5 +/- 0.2 eV, respectively. In clear contrast with the S0 state, the triplet aniline is no longer aromatic, and its protonation occurs preferentially at the ring meta-carbon site, with a proton affinity PA = 243 +/- 3 kcal/mol.     

Reduction reactions of a 1,3,5-triphosphabenzene

The reactions of the triphosphabenzene, 1,3,5-P3C3But3, with LiMH4, M = Al or Ga, lead to the triphosphabicyclo[3.1.0]hexanediyl metallate complexes, [[[Li(OEt2)][MH2(P3C3But3H2)]]2], which give exo- and endo-isomers of a triphosphabicyclo[3.1.0]hexane, P3C3But3H4 upon quenching. The related reaction of [AlH3(NMe3)] with 1,3,5-P3C3But3 affords three identifiable products, viz. a triphosphabicyclo[3.1.0]hexenyl complex, [AlH2(P3C3But3H)(NMe3)], and two triphosphabicyclo[3.1.0]hexanediyl complexes, [AlH(P3C3But3H2)(NMe3)] and [Al2H4(P3C3But3H2)(NMe3)]. In contrast, the reactions of 1,3,5-P3C3But3 with either [GaH3(quin)], quin = quinuclidine, or Me3SnH lead only to the triphosphabicyclo[3.1.0]hexenyl complexes, [GaH2(P3C3But3H)(quin)] and [Me3Sn(P3C3But3H)]. Quenching of the former affords a triphosphabicyclo[3.1.0]hexene, P3C3But3H2, while quenching the latter gives its triphosphacyclohexa-1,4-diene valence isomer. Treatment of 1,3,5-P3C3But3 with "GaI" yields a GaI3 complex of the triphosphahexa-1,4-diene, [GaI3(P3C3But3H2)], whilst treatment with the anionic Ga(I) heterocycle, [:Ga[N(Ar)C(H)]2]-, Ar = C6H3Pri2-2,6, affords the known diphospholyl anion, [1,3-P2C3But3]- via a P-abstraction from the triphosphabenzene. Finally, reaction of the 1,3,5-triphosphacyclohexane, [P(OEt)C(H)(But)]3, with thionyl chloride yields the unusual lambda5, lambda5, lambda5-1,3,5-triphosphacyclohexane, [P(O)(Cl)C(H)(But)]2[P(OEt)(S)C(H)(But)]. Suggestions as to the mechanisms of a number of these reduction reactions are made and the crystal structures of seven compounds are reported.     

Preparation of tungsten alkyl alkylidene alkylidyne complexes and kinetic studies of their formation

An equilibrium mixture of alkyl alkylidyne W(CH2SiMe3)3(CSiMe3)(PMe3) (1a) and its bis(alkylidene) tautomer W(CH2SiMe3)2(=CHSiMe3)2(PMe3) (1b) has been found to undergo an alpha-hydrogen abstraction reaction in the presence of PMe3 to form alkyl alkylidene alkylidyne W(CH2SiMe3)(=CHSiMe3)(CSiMe3)(PMe3)2 (2). In the presence of PMe3, the formation of 2 follows first-order kinetics, and the observed rate constant was found to be independent of the concentration of PMe3. The activation parameters for the formation of 2 are Delta H = 28.3(1.7) kcal/mol and Delta S = 3(5) eu. In the presence of PMe2Ph, an equilibrium mixture of W(CH2SiMe3)3(CSiMe3)(PMe2Ph) (3a) and its bis(alkylidene) tautomer W(CH2SiMe3)2(=CHSiMe3)2(PMe2Ph) (3b) was similarly converted to W(CH2SiMe3)(=CHSiMe3)(CSiMe3)(PMe2Ph)2 (4). The observed rate of this reaction was also independent of the concentration of PMe2Ph. These observations suggest a pathway in which the tautomeric mixtures 1a,b and 3a,b undergo rate-determining, alpha-hydrogen abstraction, followed by phosphine coordination, resulting in the formation of the alkyl alkylidene alkylidyne complexes 2 and 4.     

取代基对氮和氧自由基稳定性影响的理论研究

用MNDO方法，全构型优化，研究了15个氮自由基4-RC6H4NH，和15个氧自由基4-RC6H4O（R＝－H；－OCH3，－Cl，－F，－CN，－COCH3，－NO2，－CH3，－CF3，－SCH3，－C6H5，－Nh2，－BH2，－PH2，－SiH3）的稳定化能．结果表明：－NH2，－CH3，－OCH3，－F基团对自由基起稳定化作用，－CF3，－NO2；－CN，－COCH3，－BH2基团对自由基起去稳定化作用．苯基对氧自由基有较大的稳定化作用，而对氮自由基的稳定性影响较小．－SCH3，－PH2，－SiH3，－Cl基团表现弱的去稳定化作用．计算和实验结果基本相符．     

Mg-Al-CO_3与Zn-Al-CO_3水滑石热稳定性差异的研究

层状双金属氢氧化物（ Layered double hydroxides,简称 LDHs）是一类近年来发展迅速的阴离子型粘土,又称水滑石,其组成通式为： [M? 1-xM? x(OH)2]x＋ Ax/nn-mH2O,其中 M?是二价金属离子, M?是三价金属离子, An－是阴离子。这种材料是由相互平行的层板组成,层板带有永久正电荷;层间具有可交换的阴离子以维持电荷平衡。通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛用作催化剂、吸附剂及油田化学品等,已引起人们的关 注 [1～ 4]。有关 Mg-Al-CO3与 Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道 [1…     

The synthesis of oxides of sulfolene and some of its methyl derivatives

The synthesis of the oxides of 3-sulfolene, 2-methyl-3-sulfolene, and 3-methyl-3-sulfolene by the reaction of the corresponding 3-sulfolenes with peracetic acid has been described.     

Application of extraction chromatography to the separation of thorium and uranium dissolved in a solution of high salt concentration

Extraction chromatography with commercially available UTEVA resin (for uranium and tetravalent actinide) was applied for the separation of Th and U from control solutions prepared from a multi-element control solution and from sample solutions of solidified simulated waste. Thorium and U in control solutions with 1-5mol/dm(3) HNO(3) were extracted with UTEVA resin and recovered with a solution containing 0.1mol/dm(3) HNO(3) and 0.05mol/dm(3) oxalic acid to be separated from the other metallic elements. Extraction behavior of U in the sample solutions was similar to that in the control solutions, but extraction of Th was dependent on the concentration of HNO(3). Thorium was extracted from 5mol/dm(3) HNO(3) sample solutions but not from 1mol/dm(3) HNO(3) sample solutions. We conjecture that thorium fluoride formation interferes with extraction of Th. Addition of Al(NO(3))(3) and Fe(NO(3))(3), which have higher stability constant with fluoride ion than Th, does improve extractability of Th from 1mol/dm(3) HNO(3) sample solution.     

Effects of substituents on the stability of phosphoranyl radicals

The effect of substituents on the geometries, apicophilicities, radical stabilization energies, and bond dissociation energies of (*)P(CH(3))(3)X (X = CH(3), SCH(3), OCH(3), OH, CN, CF(3), Ph) were studied via high-level ab initio molecular orbital calculations. Two alternative definitions for the radical stabilization energy (RSE) were considered: the standard RSE, in which radical stability is measured relative to H-P(CH(3))(3)X, and a new definition, the alpha-RSE, which measures stability relative to P(CH(3))(2)X. We show that these alternative definitions yield almost diametrically opposed trends; we argue that alpha-RSE provides a reasonable qualitative measure of relative radical stability, while the standard RSE qualitatively reflects the relative strength of the P-H bonds in the corresponding H-P(CH(3))(3)X phosphines. The (*)P(CH(3))(3)X radicals assume a trigonal-bipyramidal structure, with the X-group occupying an axial position, and the unpaired electron distributed between a 3p(sigma)-type orbital (that occupies the position of the "fifth ligand"), and the sigma orbitals of the axial bonds. Consistent with this picture, the radical is stabilized by resonance (along the axial bonds) with configurations such as X(-) P(*+)(CH(3))(3) and X(*) P(CH(3))(3). As a result, substituents that are strong sigma-acceptors (such as F, OH, or OCH(3)) or have weak P-X bonds (such as SCH(3)) stabilize these configurations, resulting in the largest apicophilicities and alpha-RSEs. Unsaturated pi-acceptor substituents (such as phenyl or CN) are weakly stabilizing and interact with the 3p(sigma)-type orbital via a through-space effect. As part of this work, we challenge the notion that phosphorus-centered radicals are more stable than carbon-centered radicals.     

Ab initio molecular orbital study of the reactivity of active alkyl groups. V. Nitrosation mechanism of acetone with syn-form of methyl nitrite

The mechanisms of nitrosation of acetone through sodium enolate [CH3CO1CH2]-Na+ (1) or naked enolate [CH3CO1CH2]- (2) with methyl nitrite CH3O3NO2 (3), and the reactivity of the syn-form of 3 (syn-3) during the C-N bond formation process were investigated using ab initio molecular orbital (MO) methods. Our results have demonstrated the predominant formation of E-1-hydroxyimino-2-oxo-propane CH3COCH=NOH (4E) when the complex [CH3CO1CH2NO2(O3CH3)]-Na+ was produced kinetically via a metal-chelated pericyclic transition state (TS(CHELATED)), in which the O3 atom of syn-3 was coordinated to the Na+ atom of 1.     

二甲基甲酰胺中四种钕盐的电导

通过电导测量研究了四种钕盐：Nd(CF3SO3)3、Nd(ClO4)3、Nd(NO3)3和NdCl3在极性非质子溶剂DMF中的电导性质.利用线性拟合方法求得在25 ℃下Nd(CF3SO3)3和Nd(ClO4)3的极限摩尔电导率分别为278.8和 280.7 S•cm2•mol－1.用间接方法求得Nd(NO3)3 与NdCl3 的极限摩尔电导率分别为297.2和287.3 S•cm2 •mol－1.在25～65 ℃温度范围内，Nd(CF3SO3)3和Nd(ClO4)3的电导率随温度呈线性变化. Nd(NO3)3和NdCl3的电导行为表现出明显的离子缔合.     

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO

The electronic dipole transition moment functions of the A ²Π-X ²Σ⁺, B ²Σ⁺-X ²Σ⁺ and B ²Σ⁺-A ²Π transitions and the dipole moment function of the X ²Σ⁺ state of CO⁺ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B ²Σ⁺ and A ²Π. Radiative lifetimes of vibrational levels of the X ²Σ⁺ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B ²Σ⁺ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A ²Π state are in excellent agreement with lifetimes measured with an ion trap technique.     

稀土离子对甲醇电氧化的影响

选择几种稀土离子作为添加剂, 研究了稀土离子对甲醇电氧化反应的影响.     

Influence of the counteranion on the formation of polymeric networks by metal complexes of hexamethylenebis(acetamide)

An investigation into the anion dependence of the network-forming ability of metal complexes of hexamethylenebis(acetamide), CH3CONH(CH2)6NHCOCH3 (HMBA), has resulted in the X-ray characterization of the compounds [Co(HMBA)3][Co(NCS)4], 1, [Nd(HMBA)3][Nd(NO3)6].2CHCl3, 2, [Co(HMBA)3][HgCl4], 3, and [Mn(HMBA)3][HgBr4].3CHCl3, 4. The structures of compounds 1, 3, and 4 each comprise cationic frameworks formed by the bridging action of HMBA ligands binding octahedrally to the cobalt or manganese centers and, in the cases of 3 and 4, the formation of tetrahedral HgX4(2-) anions by transfer of the respective halide ions from Co or Mn to Hg. Complete anion (NO3-) transfer between Nd centers is also a key factor in the structure of 2, which forms a cationic 3-D network of HMBA-bridged octahedrally coordinated Nd centers with occluded [Nd(NO3)6]3- anions. These types of inter-metal-anion transfer, with consequent complex counteranion formation, appear to facilitate the network-forming ability of the metal-HMBA cationic arrays.     

Synthesis and cytotoxic properties of derivatives of the tert-butyl ester of 7-alkylidene-3-methyl-3-cepheme-4-carboxylic acid

Sulfones of the tert-butyl esters of 7-arylmethylene-and 7-(2-furyl)methylene-3-methyl-3-cepheme-4-carboxylic acid were obtained by the condensation of the tert-butyl ester of 3-methyl-7-oxo-3-cepheme-4-carboxylic acid with arylmethylene-and 2-furylidenetriphenylphosphoranes and subsequent oxidation of the intermediate products by meta-chloroperbenzoic acid. The combination of the tert-butyl esters of 7E-bromomethylene-and 7,7-dibromomethylene-3-methyl-1,1-dioxo-3-cepheme-4-carboxylic acids with trimethylsilylacetylene under conditions of the Sonogashira reaction gave the tert-butyl esters of 3-methyl-1,1-dioxo-7E-(3-trimethylsilyl-2-propynylidene)-3-cepheme-4-carboxylic acid and 3-methyl-1,1-dioxo-7-[1,5-bis(trimethylsilyl)-1,4-pentadiyn-3-ylidene]-3-cepheme-4-carboxylic acid. The Vilsmeier reagent was used to incorporate the dimethylaminomethylene group at C-2 of the 7Z-and 7E-isomers of the tert-butyl ester of 7-(4-chlorophenyl)methylene-3-methyl-1,1-dioxo-3-cepheme-4-carboxylic acid. The cytotoxic properties of the derivatives of the tert-butyl ester of 7-alkylidene-3-methyl-3-cepheme-4-carboxylic acid in regard to cancer and normal cells in vitro depends on the structure and 7Z-or 7E-isomerism of the substituent in the 7-alkylidene group as well as the presence of a dimethylaminomethylene group at C-2 of the 3-cepheme system.     

A novel classification of Lewis acids on the basis of activity and selectivity

Group 3-15 metal chlorides (Lewis acids) were classified on the basis of activity and aldehyde- and aldimine-selectivity in an addition reaction of a silyl enol ether. Based on the experimental results, metal chlorides (Lewis acids) were classified as follows: A, active; B, weak; C, inactive for the activation of the aldehyde and/or aldimines. Groups A and B were further divided into A-1 or B-1 (aldehyde-selective), A-2 or B-2 (aldimine-selective), and A-3 or B-3 (neutral). The final classification is as follows: A-1, BCl3, AlCl3, TiCl4, GaCl3, ZrCl4, SnCl4, SbCl5, SbCl3, HfCl4, ReCl5; A-2, ScCl3, FeCl3, InCl3, BiCl3; A-3, NbCl5, MoCl3. MoCl5, SnCl2, TaCl5, WCl5. WCl6, ReCl3, TlCl3; B-1, none; B-2, SiCl4, FeCl2, CoCl2, CuCl, CuCl2, GeCl4, YCl3, OsCl3, PtCl2; B-3, ZnCl2, RuCl3; C, VCl3, CrCl3, MnCl2, NiCl2, RhCl3, PdCl2, AgCl, CdCl2, IrCl3, AuCl, HgCl2, HgCl, PbCl2. This classification has revealed several new fundamental aspects of elements (metal chlorides) as Lewis acids.     

Absolute structure of panaxytriol

Diastereomeric mixture at C-3 of (9R,10R)-panaxytriol acetonide (3) and (9S,10S)-panaxytriol acetonide (4) were enantioselectively acetylated to give (3R)-acetates (3a-Ac, 4a-Ac) and (3S)-alcohols (3b, 4b) by enzyme mediated-acetylation using CHIRAZYME and vinyl acetate, respectively. Hydrolysis of (3R)-acetate (3a-Ac, 4a-Ac) with CHIRAZYME and phosphate buffer afforded (3R)-alcohols (3a, 4a), respectively. Deprotection of panaxytriol acetonides (3a, 3b, 4a, 4b) gave panaxatriol and its isomers, respectively. Comparison of optical rotation values of the synthetic panaxatriols with that of the natural one confirmed that the absolute configuration of panaxytriol sould be 3R,9R,10R.     

Synthesis and characterization of a family of structurally characterized dysprosium alkoxides for improved fatigue-resistance characteristics of PDyZT thin films

Using either an ammoniacal route, the reaction between DyCl3, Na0, and HOR in liquid ammonia, or preferentially reacting Dy(N(SiMe3)2)3 with HOR in a solvent, we isolated a family of dysprosium alkoxides as [Dy(mu-ONep)2(ONep)]4 (1), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(THF)]2(mu-ONep) (2), (ONep)2Dy[(mu3-ONep)(mu-ONep)Dy(ONep)(py)]2(mu-ONep) (3), [Dy3(mu3-OBut)2(mu-OBut3(OBut)4(HOBut)2] (4), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(THF)2] (5), [Dy3(mu3-OBut)2(mu-OBut)3(OBut)4(py)2] (6), (DMP)Dy(mu-DMP)4[Dy(DMP)2(NH3)]2 (7), [Dy(eta6-DMP)(DMP)2]2 (8), Dy(DMP)3(THF)3 (9), Dy(DMP)3(py)3 (10), Dy(DIP)3(NH3)2 (11), [Dy(eta6-DIP)(DIP)2]2 (12), Dy(DIP)3(THF)2 (13), Dy(DIP)3(py)3 (14), Dy(DBP)3(NH3) (15), Dy(DBP)3 (16), Dy(DBP)3(THF) (17), Dy(DBP)3(py)2 (18), [Dy(mu-TPS)(TPS2]2 (19), Dy(TPS)3(THF)3 (20), and Dy(TPS)3(py)3 (21), where ONep = OCH2CMe3, OBut) = OCMe3, DMP = OC6H3(Me)(2)-2,6, DIP = OC6H3(CHMe2)(2)-2,6, DBP = OC6H3(CMe3)(2)-2,6, TPS = OSi(C6H5)3, tol = toluene, THF = tetrahydrofuran, and py = pyridine. We were not able to obtain X-ray quality crystals of compounds 2, 8, and 9. The structures observed and data collected for the Dy compounds are consistent with those reported for its other congeners. A number of these precursors were used as Dy dopants in Pb(Zr0.3Ti0.7)O3 (PZT 30/70) thin films, with compound 12 yielding the highest-quality films. The resulting Pb0.94Dy0.04(Zr0.3Ti0.7)O3 [PDyZT (4/30/70)] had similar properties to PZT (30/70), but showed substantial resistance to polarization reversal fatigue.