Synthesis and reactivity of rare earth metal alkyl complexes stabilized by anilido phosphinimine and amino phosphine ligands

Anilido phosphinimino ancillary ligand H2L1 reacted with one equivalent of rare earth metal trialkyl [Ln{CH2Si(CH3)(3)}(3)(thf)(2)] (Ln = Y, Lu) to afford rare earth metal monoalkyl complexes [L(1)LnCH(2)Si(CH3)(3)(THF)] (1a: Ln = Y; 1b: Ln = Lu). In this process, deprotonation of H2L1 by one metal alkyl species was followed by intramolecular C-H activation of the phenyl group of the phosphine moiety to generate dianionic species L-1 with release of two equivalnts of tetramethylsilane. Ligand L-1 coordinates to Ln(3+) ions in a rare C,N,N tridentate mode. Complex 1a reacted readily with two equivalents of 2,6-diisopropylaniline to give the corresponding bis-amido complex [(HL1)LnY(NHC(6)H(3)iPr(2)-2,6)(2)] (2) selectively, that is, the C-H activation of the phenyl group is reversible. When 1a was exposed to moisture, the hydrolyzed dimeric complex [{(HL1)Y(OH)}(2)](OH)(2) (3) was isolated. Treatment of [Ln{CH2Si(CH3)(3)}(3)-(thf)(2)] with amino phosphine ligands HL2-R gave stable rare earth metal bisalkyl complexes [(L2-R)Ln{CH2Si(CH3)(3)}(2)(thf)] (4a: Ln=Y, R=Me; 4b: Ln=Lu, R=Me; 4c: Ln=Y, R=iPr; 4d: Ln=Y, R=iPr) in high yields. No proton abstraction from the ligand was observed. Amination of 4a and 4c with 2,6-diisopropylaniline afforded the bis-amido counterparts [(L2-R)Y(NHC(6)H(3)iPr(2)-2,6)(2)(thf)] (5a: R=Me; 5b: R=iPr).

Rare earth metal complexes bearing thiophene-amido ligand: Synthesis and structural characterization

2,6-Diisopropyl-N-(2-thienylmethyl) aniline ( H2L) has been prepared, which reacted with equimolar rare earth metal tris( alkyl)s, Ln( CH2SiMe3)(3)( THF)(2), afforded rare earth metal mono( alkyl) complexes, LLn(CH2SiMe3)(THF)(3) ( 1: Ln = Lu; 2: Ln = Y). In this process, H2L was deprotonated by one metal alkyl species followed by intramolecular C-H activation of the thiophene ring to generate dianionic species L2- with the release of two tetramethylsilane. The resulting L2- combined with three THF molecules and an alkyl unit coordinates to Y3+ and Lu3+ ions, respectively, in a rare N,C-bidentate mode, to generate distorted octahedron geometry ligand core. Whereas, with treatment of H2L with equimolar Sc(CH2SiMe3)(3)( THF)(2), a heteroleptic complex ( HL)( L) Sc( THF) ( 3) was isolated as the main product, where the dianionic L2- species bonds to Sc3+ via chelating N, C atoms whilst the monoanionic HL connects to Sc3+ in an S,N-bidentate mode. All complexes 1-3 have been characterized by NMR spectroscopy and X-ray diffraction analysis.

Efficient synthesis of highly substituted pyrrolin-4-ones via PIFA-mediated cyclization reactions of enaminones

A convenient and efficient synthesis of highly substituted pyrrolin-4-ones is developed via the PIFA-mediated cyclization reactions of readily available enaminones, and a mechanism involving sequential cleavage of N-C bond, formation of new N-C bond, intramolecular addition reaction, and benzilic acid type rearrangement is proposed.

The relation between formal potential and structure of indophenols and molecular mechnism of electrooxidation

The molecular structural parameters of indophenol and its derivatives were calculated by semi-empirical molecular orbital quantum chemical method,The relation between molecular structural parameters and formal potentials was analyzed by principal factor analysis and multiple Linear regression method. It was found that the formal potential of indophenols has a good relation with two-center electron exchange energy, E-ex (2), resonance energy of O-C bond, E-ex (C-1-O), and molecular ionization potential, I-p, among 19 moleclular structural parameters. The regression equation is E-0' = 1. 47 x 10 (-3) E-ex (two) - 5. 74 x 10 (-2) E-ex (C-1 - O) - 1. 41 x 10 (-2) I-p with RC = 0. 9999 and SD = 0. 00424. It was confirmed by the relation between structure parameters and formal potentials, and the thermodynamic stability of its intermediate products that the H (+) ionization is prior to the electron transfer step in the oxidation mechanism.

Low-temperature oxidation of methane to form formaldehyde: role of Fe and Mo on Fe-Mo/SiO2 catalysts, and their synergistic effects

The partial oxidation of methane with molecular oxygen was performed on Fe-Mo/SiO2 catalysts. Iron was loaded on the Mo/SiO2 catalyst by chemical vapor deposition of Fe-3(CO)(12). The catalyst showed good low-temperature activities at 723-823 K. Formaldehyde was a major condensable liquid product on the prepared catalyst. There were synergistic effects between iron and molybdenum in Fe-Mo/SiO2 catalysts for the production of formaldehyde from the methane partial oxidation. The activation energy of Mo/SiO2 decreased with the addition of iron and approached that of the Fe/SiO2. The concentration of isolated molybdenum species (the peak at 1148 K in TPR experiments) decreased as the ion concentration increased and had a linear relationship with the selectivity of methane to formaldehyde. The role of Fe and Mo in the Fe-Mo/SiO2 catalyst was proposed: Fe is the center for the C-H activation to generate reaction intermediates, and Mo is the one for the transformation of intermediates into formaldehyde. Those phenomena were predominant below 775 K.

In-situ microscopic FTIR spectroelectrochemistry of ascorbic acid in poly(ethylene glycol)/LiClO4 electrolyte paste and in the presence of dispersed cobalt hexacyanoferrate microcrystalline powder

In-situ microscopic FTIR spectroelectrochemical technique(MFTIRs) was applied to studying the electrochemical oxidation of ascorbic acid(AA) in poly(ethylene glycol)(PEG) paste at a 100 mu m diameter Pt disk electrode. Using this technique, the catalytic ability of cobalt hexacyanoferrate(CoHCF) microcrystalline toward AA oxidation was also studied, it was found that the dispersed CoHCF powder in the PEG paste can generate well-shaped thin-layer cyclic voltammetric waves with the peak height proportional to the scan rate, corresponding to the Fe centered redox reactions. This oxidation step catalyzed the AA oxidation. Also, this pasted CoHCF powder generated well-resolved in-situ MFTIRs spectra, by which a chemical interaction between C = C bond of AA ring and CoHCF lattice was revealed. A corresponding surface docking mechanism for the catalytic reaction has been proposed.

SYNTHESIS AND MOLECULAR-STRUCTURE OF NBU2[(MEO)3C6H2C(O)N2CHC6H4O]SN FORMED IN THE REACTION OF DI-N-BUTYLTIN(IV) OXIDE WITH 3,4,5-TRIMETHOXY-BENZOYL SALICYLAHYDRAZONE

The title complex was synthesized and characterized by H-1, C-13, Sn-119 NMR and IR spectra. A single crystal X-ray diffraction study confirmed its molecular structure and revealed that 3,4,5-trimethoxy-benzoyl salicylahydrazone was a tridentate and approximately planar ligand. The complex crystallizes in the triclinic space group P1BAR with a = 9.208(3), b = 12.536(2), c = 12.187(4) angstrom, alpha = 113.12(2), beta = 90.58(2), gamma = 81.42(2), V = 1277.5(6) angstrom, Z = 2. The structure was refined to R = 0.033 and R(w) = 0.041 for 3944 observed independent reflections. The tin atom has a distorted trigonal bipyramidal coordination. The Sn-C bond lengths are 2.129(5) and 2.113(5) angstrom (av. 2.121(5) angstrom), the C-Sn-C angle is 123.3(2); the bond length between the tin atom and the chelating nitrogen is 2.173(3) angstrom. Two chain carbon atoms and the chelating nitrogen atom occupy the basal plane. The skeleton of two erect oxygen atoms and the tin atom is bent (O-Sn-O angle = 153.5(1)). In the complex, the ligand exists in the enol-form.

PREPARATION AND MOLECULAR-STRUCTURE OF METHYLBIS(TERT-BUTYLCYCLOPENTADIENYL)NEODYMIUM AND METHYLBIS(TERT-BUTYLCYCLOPENTADIENYL)GADOLINIUM

Bis(t-butylcyclopentadienyl)lanthanide chloride (Ln = Nd or Gd) reacts with one equivalent of methyllithium in ether/tetrahydrofuran to give the complex [(C5H4tBu)2LnCH3]2 (Ln = Nd or Gd). The structure of [(C5H4tBu)2NdCH3]2 has been determined by X-ray analysis. The crystals are monoclinic of space group Cm with a = 9.538(2), b = 23.298(4), c = 9.505(3) angstrom, beta = 119.53(2)-degrees, V = 1828.0(7) angstrom 3, D(calc.) = 1.458 g/cm3 and Z = 2 for the dimer. The two (C5H4tBu)2Nd units in the dimer are connected by asymmetrical methyl bridges with independent Nd-C bond lengths of 2.70(2) and 2.53(2) angstrom and Nd-C-Nd angles of 94.7(9) and 87.3(6)-degrees.

CONFORMATION OF PHENYL RINGS IN THE HELICAL CHAIN POLYMER POLY(TRIPHENYLMETHYL METHACRYLATE)

The conformation of phenyl rings in the side groups of the helical chain polymer poly(tripenyl-methyl methacrylate) (1) in solution was studied by spectroscopic methods. According to the Raman spectrum the phenyl rings of 1 and triphenylmethyl methacrylate in solution have the same depolarization ratio at 1002 cm-1. The electronic spectra (ultraviolet and fluorescence) of 1 are similar to those of model substances, except for the "red shift" of the spectra of about 5 nm. It was concluded that the phenyl rings can rotate around the phenyl-C bond.

Effect of nano-TiO(2)on MP-25 resin

MP-25 resin is a chlorine-containing polymer widely used in coatings. The effects of two types of nano-TiO2 (P-25 and RM301 LP) on MP-25 were studied with saline immersion, UV irradiation, and electrochemical impedance spectroscopy. UV irradiation was evaluated in terms of gloss change and X-ray photoelectron spectroscopy (XPS). The results indicate that, compared to pigment R-930 TiO2, P-25 reduced the immersion resistance and accelerated UV aging of the MP-25 coating, whereas RM301 LP showed the opposite effects. XPS analysis showed that MP-25 resin degraded under UV irradiation via dechlorination and C-C bond breakage, similarly to poly(vinyl chloride), but RM301 LP could inhibit the aging of MP-25 to a certain extent. A skin effect of oxygen and chlorine was identified in MP-25 resin by XPS. RM301 LP could improve the impedance of the MP-25 coating because of its excellent fill capacity. Hence, rutile nano-TiO2 RM301 LP represents an excellent additive for MP-25 resin. (c) 2007 Wiley Periodicals, Inc.

苯乙酮、氨甲酸酯参与的直接Mannich反应

Mannich反应是有机化学中最重要的碳-碳键形成反应，其产物是合成手性胺的通用中间体。间接Mannich反应使用不稳定的预制烯醇等当体，以未修饰的酮为给体的直接方法将增强Mannich反应的效率。针对低活性苯乙酮、氨甲酸酯参与的直接Mannich反应，研究工作将更具挑战性。 在前期实验中，我们发现Lewis酸-NbCl5可高效催化苯乙酮、芳香醛、芳香胺三组分直接Mannich反应，反应在环境温度下进行，高收率获得Mannich碱。这是以苯乙酮参与的Mannich反应中，实现催化量Lewis酸催化的首次报道。该方法高效且操作简单。但就底物而言，对易去保护、低活性的氨甲酸酯类底物收率较低。我们设想Brønst酸可解决此类底物问题。令人高兴的是，杂多酸可高效催化芳香酮、芳香醛、氨甲酸酯三组分直接Mannich反应，反应在环境温度下进行，高收率获得N-保护的β-氨基酮。该方法底物范围广泛，普适性强且催化剂便宜。 基于杂多酸在苯乙酮、氨甲酸酯为底物直接Mannich反应中的高效性，我们设想杂多酸与功能化的手性有机小分子-手性伯胺组装可解决催化剂回收问题，同时实现不对称催化。实验结果表明，非共价键固载手性伯胺不能有效催化苯乙酮为底物的直接Mannich反应，无论是对映选择性还是收率均较低。随后，我们以丙二酸酯及α-氨基砜为底物，以增强底物活性，同时绕开亚胺的不稳定性。辛可宁伯胺以氢键双活化底物，有效催化原位产生氨甲酸酯类亚胺与丙二酸酯的Mannich反应，高收率获得Mannich碱，ee值中等。 我们采用逐步解决问题的策略解决Mannich反应中的部分问题并在Lewis酸催化、Brønst酸催化、非共价键固载手性伯胺催化及手性伯胺氢键催化的直接Mannich反应中做出了有益探索。 The Mannich reactions are among the most fundamental carbon-carbon bond forming reactions in organic chemistry, and the reaction products are versatile intermediates in the synthesis of chiral amines. The indirect Mannich reaction uses preformed enolate equivalents. However the preformed enolates are unstable. Thus, a direct methodology based on unmodified ketone donors would enhance the efficiency of the Mannich reaction. Especially researches for the directed Mannich reactions of acetophenone, carbamate, which own lower activities, will be more challengeable. In the initial experiments, we found an efficient Lewis acid-NbCl5 which could catalyze three-component Mannich-type reaction of acetophenone, aromatic aldehydes and aromatic amines at ambient temperature in high yields. This is the first report that use catalytic amount of Lewis acid in the Mannich reactions of .acetophenone. The method reported is not only simple to operate but also efficient. However, as far as amines are concerned, the substrates of carbamates which can be deprotected more easily and less reactive than amines give low yields. We envisaged that Brønsted acid would resolve this problem. Pleasingly, heteropoly acids (HPA) efficiently catalyzed one-pot three-component Mannich reactions of aryl aldehydes, aryl ketones, and carbamates at ambient temperature and afforded the corresponding N-protected β-amino ketones in good to excellent yields. This method provides a novel and improved modification of three-component Mannich reactions in terms of a wide scope of aldehydes, ketones and carbamates, economic viability. Based on the high efficiency of heteropoly acids in the Mannich reaction of acetophenone and carbamates, we envisaged that if HPA were combined with functionalized chiral organocatalysts–chiral primary amines the assemblies may be able to act as recoverable asymmetric organocatalysts. The results of exprimentals showed that noncovalently supported heterogeneous chiral primary amine couldn’t effectively catalyze the Mannich reactions which own two the substrate of acetophenone regardless of enantioselectivity and yield. Then, we employed malonates and α-amido sulfones as substrates to enhance reactivity of substrates and circumvent the instability of imines. A moderately enantioselective and highly yield Mannich reaction with in situ generation of carbamate-protected imines from stable α-amido sulfones catalyzed by cinchonine primary amine catalyst was developed. It is noteworthy that cinchonine primary amine can dual activate substrates through H-bond activation and thus promote the reaction. We applied step-by-step-strategy to resolve some problems in the Mannich reactions and did some instructive explorations in Lewis acid catalysis, Brønst acid catalysis, noncovalently supported heterogeneous chiral primary amine catalysis and chiral primary amine as hydrogen-bond catalysis.

An Efficient Ullmann-Type C-O Bond Formation Catalyzed by an Air-Stable Copper(I)-Bipyridyl Complex

An efficient O-arylation of phenols and aliphatic alcohols with aryl halides was developed that uses an air-stable copper(I) complex as the catalyst. This arylation reaction can be performed in good yield in the absence of Cs2CO3. A variety of functional groups are compatible with these reaction conditions with low catalyst loading levels.

Surface-enhanced resonance Raman spectroscopy and spectroscopy study of redox-induced conformational equilibrium of cytochrome c adsorbed on DNA-modified metal electrode

The redox-induced conformational equilibrium of cytochrome c (cyt c) adsorbed on DNA-modified metal electrode and the interaction mechanism of DNA with cyt c have been studied by electrochemical, spectroscopic and spectroelectrochemical techniques. The results indicate that the external electric field induces potential-dependent coordination equilibrium of the adsorbed cyt c between its oxidized state (with native six-coordinate low-spin and non-native five-coordinate high-spin heme configuration) and its reduced state (with native six-coordinate low-spin heme configuration) on DNA-modified metal electrode. The strong interactions between DNA and cyt c induce the self-aggregation of cyt c adsorbed on DNA. The orientational distribution of cyt c adsorbed on DNA-modified metal electrode is potential-dependent, which results in the deviation from an ideal Nernstian behavior of the adsorbed cyt c at high electrode potentials. The electric-field-induced increase in the activation barrier of proton-transfer steps attributed to the rearrangement of the hydrogen bond network and the self-aggregation of cyt c upon adsorption on DNA-modified electrode strongly decrease the interfacial electron transfer rate.