Synthesis of Glycosylphosphine Oxides and Related Compounds

The benzyl-protected glycosyl acetates 1 , 6 , 11 , and 15 react with MeOPPh₂ under catalysis by TMSOTf to yield diastereoselectively the glycosylphosphine oxides 2 , 3 , 8 , 12 , 13 , and 16 , with a strong preference for the 1,2-cis-configurated anomers. Hydrogenolysis of the major products gave the crystalline, unprotected phosphine oxides 4 , 9 , 14 , and 17 , of which 4 was transformed in to the acetate 5 , and 9 into the benzoate 10 . The benzylated phosphine oxides 4 , 8 , 12 , and 16 were reduced with Cl₃SiH in the presence of a tertiary amine to form the phosphines 18 , 21 , 24 , and 26 , which were transformed into the phosphine sulfides 19 , 22 , 25 , and 27 . Moreover, 18 and 21 , were characterized as the borane adducts 20 , and 23 . The structure of the (arabinofuranosyl)phosphine oxide 12 , the corresponding sulfide 25 , and of the borane complex 20 were established by X-ray analysis. According to NMR spectroscopy, the equatorial pyranosylphosphine oxide 8 , the sulfide 22 , and the borane complex 23 adopt a ⁴C₁ conformation. The axial phosphine oxide 2 is a flattened ⁴C₁, the sulfide 19 exists as a B_2,5, and the borane complex 20 is a flattened ⁴C₁ in the solid sate and a B_2,5 in solution. Thus, the conformational behavior of these α-D -glucopyranose derivatives reflects the steric requirement of the P-substituents.     

Structures and Unexpected Dynamic Properties of Phosphine Oxides Adsorbed on Silica Surfaces

Solid‐state NMR spectroscopy of selected phosphine oxides adsorbed on silica surfaces establishes the surface mobilities, even of phosphine oxides with high melting points. Crystal structures of the adducts Ph₃PO ? HOSiPh₃ and Cy₃PO ? H₂O indicate that the interactions with silica involve hydrogen bonding of the P?O group to adsorbed water and surface silanol groups.     

Quantum-Chemical Study of the Structure of Cyanophosphines and Their Oxides

The structure of cyanophosphines and their oxides was studied by ab initio (RHF/6-31G^**) and semiempirical (PM3) methods. Both methods predict that MeOP(CN)₂, (MeO)₂PCN, and (MeO)₂P(O)CN exist in noneclipsed antiperiplanar and synclinal conformations. The calculation results nicely agree with measured dipole moments and Kerr constants of these compounds. The phenyl and diphenyl derivatives PhP(CN)₂, Ph₂PCN, Ph(Et)PCN, and Ph₂P(O)CN prefer forms in which the phenyl ring plane is eclipsing the phosphorus lone electron pair or the phosphoryl bond. The interactions of the phosphorus lone electron pair with the phenyl ring and with the cyano group are lacking in the title compounds.     

Atom-Economic Synthesis of Tris[2-(organylthio)ethyl]phosphine Oxides from Phosphine and Vinyl Sulfides

Abstract

Phosphine, generated from elemental phosphorus in the system KOH-toluene-H₂O, reacts with vinyl sulfides under free radical conditions (AIBN, dioxane, 65–70°C, atmospheric pressure) to form regiospecifically tris[2-(organylthio)ethyl]phosphines, which are readily oxidized in air to corresponding tris[2-(organylthio)ethyl]phosphine oxides.     

Structures and Dynamics of Secondary and Tertiary Alkylphosphine Oxides Adsorbed on Silica

The three secondary phosphine oxides [CH₂=CH(CH₂)₄]₂HPO ( 1 ), [CH₂=CH(CH₂)₅]₂HPO ( 2 ), and [CH₂=CH(CH₂)₆]₂HPO ( 3 ), and two diphosphine dioxides, {[CH₂=CH(CH₂)₆]₂PO(CH₂)₇}₂ ( 4 ) and {[CH₂=CH(CH₂)₆]₂PO(CH₂)₄}₂ ( 5 ), incorporating long methylene chains, are described. The single crystal X‐ray structures of 1 , 2 , and 5 have been determined. The phosphine oxides 3 , 4 , and 5 have been adsorbed on silica in submonolayer quantities to give 3 a – 5 a . The ¹H, ¹³C, and ³¹P solid‐state NMR spectra of polycrystalline 3 – 5 have been analyzed and compared with those of 3 a – 5 a . The changes of the solid‐state NMR characteristics upon adsorption and the surface mobilities of the phosphine oxides are discussed.     

Binaphthyl-Substituted Chiral Phosphines and Oxides from Binaphthophooles and Nucleophiles

Binaphthophospholes 1 are the starting compounds for the synthesis of chiral phosphine oxides 3 or phosphines 4 via reaction of phospholium salts 2 with nucleophiles. The binaphthyl residue acts as a stereochemical probe for monitoring the integrity of the phosphorus stereocenter.     

Mixed Titanium and Phosphorus Oxides. II. — The Effect of pH Values of Solutions on Surface Acidity

A series at mixed oxides of titanium and phosphorus were prepared by co-precipitation method accompanying refluxing treatment. The effect of the pH values of the solutions on the structures, compositions, and surface acidities of the resultants compounds was determined. The samples were characterized by BET surface area measurement, X-ray powder diffraction (XRD) for structural analysis and amine-titration for surface acidities. After calcinating the oxides at 773 K, the surface acidities were attributed mainly to Ti(OH)PO₄ structure. Elemental analysis revealed that the P/Ti ratios in the samples decreased with increasing the pH value of the preparative solution. When the mixed oxides were used as catalysts for 2-propanol decomposition reaction, the highest activities were obtained over the samples prepared in the solutions with the pH values being 2 or 3. That result was in agreement with the variation in surface area and acid amount of the catalysts.     

Sodium in liquid ammonia—a versatile tool in modifications of arylphosphine oxides

A simple and practical method for modifications of tertiary arylphosphine oxides based on their reaction with sodium in liquid ammonia is presented. Depending on the structure of the starting compounds, either dearomatisation of the phenyl substituent or cleavage of a P-aryl bond from phosphorus atom can be selectively performed and the corresponding (1,4-cyclohexadien-3-yl)phosphine oxides or secondary phosphine oxides were obtained in good to excellent yields.     

Construction of P-Chiral Alkenylphosphine Oxides through Highly Chemo-, Regio-, and Enantioselective Hydrophosphinylation of Alkynes

Alkenylphosphine oxides have a wide spectrum of practical applications. However, chemo-, regio-, and enantiocontrolled construction of this structural motif still constitutes a significant synthetic challenge. Here we show that these compounds can be efficiently accessed by using a palladium/Xiao-Phos catalytic system, which leads to the highly regioselective formation of the anti-Markovnikov adducts through addition of a secondary phosphine oxide to an alkyne. Diverse (hetero)aryl and alkyl alkynes, as well as both terminal and internal alkynes can be employed as substrates. The kinetic resolution process makes it possible to produce alkenylphosphine oxide and recovered secondary phosphine oxides with high ee values. Further transformations of these two P-chiral scaffolds confirm the high practicability and application prospect of our synthetic strategies. Initial mechanistic studies strongly suggested that hydropalladation is likely responsible for the conversion process.     

Study of Electron Donor–Acceptor Complex Formation of o-Chloranil With a Series of Phosphine Oxides and Tri- n-butyl Phosphate by the Absorption Spectrometric Method

Electron donor–acceptor (EDA) complex formation of o-chloranil with six different phosphine oxides and tri-n-butyl phosphate (TBP) has been studied in CCl ₄ solution by the UV-VIS absorption spectrophotometric technique. An absorption band due to a charge–transfer (CT) transition is observed in the visible region. Utilizing the CT transition energy, the electron affinity of o-chloranil in solution has been calculated. Degrees of charge transfer, and oscillator and transition dipole strengths have also been calculated for all of the investigated EDA complexes. Except for TBP, other phosphine oxides, viz., tri-n-octyl phosphine oxide, tri-n-butyl phosphine oxide, triphenyl phosphine, octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide, octyl(phenyl)-N,N-dicyclohexylcarbamoylmethylphosphine oxide and octyl(phenyl)-N,N-diisopropylcarbamoylmethylphosphine oxide have been shown to form stable 1:1 EDA complexes with o-chloranil. The complex of TBP with o-chloranil decays slowly into a secondary product. Formation constants of the EDA complexes have been determined.     

The nature of the N?O bond in amine oxides

Despite the ubiquitous presence of amine oxides in chemistry, there is no consensus about the nature of the N O bond in these compounds. In this work, we have used electron density analysis to investigate the nature of this bond in substituted amine oxides, R₃NO, and have compared it with the nature of the N O bond in hydroxylamines, R₂NOR, and model molecules that have well-established chemical bond character. The results showed that the N O bond length and relative stability are proportional to the inductive effect of the substituents. Quantum chemical topology, natural bond orbitals (NBO), and natural resonance theory (NRT) analyses indicated that the N O bond is polar covalent in all the studied amine oxides, but the ionic contribution is different. NBO and NRT analyses revealed that molecules with more electronegative substituents have strongly delocalized N O and N R bonds, whereas molecules with electropositive substituents have localized bonds.     

碱金属助剂类型及前驱物对改性NiAl复合氧化物催化分解N2O活性的影响

制备了不同Ni/Al原子比的NiAl类水滑石样品,焙烧获得NiAl复合氧化物,用于N₂O分解反应,研究了NiAl复合氧化物组成对催化活性的影响。在活性较高的NiAl复合氧化物表面浸渍碱金属碳酸盐溶液,制备改性NiAl复合氧化物,考察了碱金属类型（Na、K、Cs）和钾前驱物（K₂CO₃、K₂C₂O₄、CH₃COOK、KNO₃）对改性催化剂活性的影响。用XRD、ICP-AES、FT-IR、BET、H₂-TPR、XPS技术表征了催化剂的组成结构。结果表明,Ni/Al原子比为2.7的NiAl复合氧化物催化活性较高;Na、K、Cs碳酸盐改性NiAl复合氧化物均提高了催化剂活性,其中K的助剂效应最强。钾前驱物对K改性NiAl复合氧化物的催化活性有显著影响,其中碳酸钾、醋酸钾、草酸钾的加入明显提高了改性催化剂的催化活性,而加入硝酸钾反而降低了催化剂活性。     

Brønsted Acid Promoted Reduction of Tertiary Phosphine Oxides

Recently, Brønsted acids, such as phosphoric acids, carboxylic acids, and triflic acid, were found to catalyze the reduction of phosphine oxides to the corresponding phosphines. In this study, we fully characterize the HCl, HOTf, and Me₂SiHOTf adducts of triphenylphosphine oxide and find that the thermally stable adduct Ph₃POH⁺OTf^– is efficiently converted into triphenylphosphine at 100 °C in the presence of readily available hydrosiloxanes. Under the same reaction conditions, also Ph₃POSiMe₂H⁺OTf^– selectively affords triphenylphosphine indicating that silylated phosphine oxides are likely intermediates in this process.     

On Mercury(I) Oxo Compounds — Quasi‐Relativistic Computational and Experimental Studies

About 60 molecular species composed of up to 10 mercury atoms and of oxygen atoms and/or of some other elements or groups (such as halogen, OH₂, OH, H, alkali, NO₃) have been investigated quantum chemically. Different density functional approaches and the ab initio SCF‐MP2 method were applied, comparing different basis sets and different atomic core sizes. It is important not to treat the Hg 5s, p, d as inactive core shells, and to use sufficiently many polarization functions. The shape of the 〉O‐Hg‐Hg‐O〈 units is not favorable concerning the formation of lattices composed of Hg^I, O and OH only. Despite its bulkiness, the OHgHgO units can easily come into contact with each other and then disproportionate. This is prevented in the so‐called ternary M‐Hg^I oxides by the embedded oxometallate (oxoacidic) anions. Furthermore, the Hg^I and Hg^II oxide bond energies are less favorable towards the stability of Hg^I oxo compounds, as compared to Hg halidic or oxoacidic compounds. Both points are not promising concerning the search for Hg^I oxides/hydroxides, although the preparation of such compounds, including spacer groups, by topochemical reactions can still not be excluded. So far, experimental efforts towards the synthesis of such a new class of compounds have only demonstrated that Hg^II is strictly preferred over Hg^I in the formation of solids of binary Hg‐O or ternary A‐Hg‐O composition (A = electropositive metal such as alkali, in contrast to M = transition or semi‐metal). This is so even if compounds containing ‘electron rich Hg^δ— atoms’ (i.e. A‐Hg amalgams) are oxidized under mild conditions.     

Application of Differential Scanning Calorimetry to the Reduction of Several Manganese Oxides

The aim of this work was to study the thermal transitions of several manganese oxides (MnO, MnOOH, Mn₂O₃, Mn₃O₄ and MnO₂) under reducing conditions. Differential scanning calorimetry (DSC) was used to analyse the transitions of some oxides into others. A comparison of the behavior of the synthetic samples with that of a natural manganese dioxide demonstrated that DSC is a quick tool for the distinction of natural manganese dioxide from synthetic γ-MnO₂ from other manganese oxides. This revised version was published online in July 2006 with corrections to the Cover Date.     

Luminescence Determination of Europium in High-Purity Yttrium and Gadolinium Oxides

ABSTRACT

A luminescence spectrometric method was developed for the determination of ultratrace amounts of europium (down to 1×10^?10 M) in high-purity yttrium and gadolinium oxides. This is based on the enhanced luminescence of europium thenoyltrifluoroacetone (TTA)-Tri-n-octyl phosphine oxide (TOPO)-Triton X-100 in the presence of terbium. The luminescence intensity is linear with europium concentration in the range 1×10^?9 to 1×10^?6 M under the recommended conditions. The optimized procedure is successfully utilized for the determination of ultratrace amounts of europium in yttrium and gadolinum oxides.     

金属氧化物与现代微电子学——过渡金属前体化合物及转化为材料的化学过程

金属氧化物薄膜如HfO₂（被称为高k电介质）是现代微电子器件的关键组件,广泛用于计算机（平板电脑,笔记本电脑和台式机）、智能电话、智能电视、汽车和医疗设备中。具有大介电常数（k）的金属氧化物已经取代了介电常数小的SiO₂（k=3.9）,从而使得微电子元件进一步小型化。过渡金属化合物在化学气相沉积（CVD）和原子层沉积（ALD）中被广泛用作前体,通过与O₂、H₂O或O₃的反应生成金属氧化物薄膜。微电子金属氧化物膜是纳米材料最广泛应用的一个领域。本文概观该领域的最新进展,包括我们对d⁰过渡金属配合物与O₂反应的研究。     

A Convenient and Selective Palladium‐Catalyzed Aerobic Oxidation of Alcohols

An efficient procedure for the oxidation of primary and secondary alcohols to aldehydes and ketones, respectively, with molecular oxygen under ambient conditions has been achieved. By applying catalytic amounts of Pd(OAc)₂ in the presence of tertiary phosphine oxides (O?PR₃) as ligands, a variety of substrates are selectively oxidized without formation of ester byproducts. Spectroscopic investigations and DFT calculations suggest stabilization of the active palladium(II) catalyst by phosphine oxide ligands.     

Preparation of Mixed Co and Cu Oxides via Thermal Decomposition of Their Oxalates,and Study of Their Catalytic Properties

Mixed oxides were prepared by the thermal decomposition of the oxalates of cobalt(II) and copper(II) coprecipitated from aqueous solution or made by mechanical mixing. The compositions and structures of the oxides were confirmed by means of TG and X-ray powder diffraction spectroscopy. The catalytic behaviour of the oxides obtained was studied by using the decomposition of H₂O₂ as a model reaction. The results were compared with those on the oxides produced from the thermal decomposition of mechanically mixed oxalates. The catalytic activities of the mixed oxides were found to be lower than that of pure cobalt oxide, but higher than that of copper oxide. This result was interpreted in terms of the relative standard reduction potential of the catalyst as compared with that of H₂O₂. The catalytic activity of the mixed oxides obtained from the coprecipitate was found to be lower than that of the oxides obtained from the mechanical mixture at the same temperature. As the temperature of preparation was increased, the catalytic activities of the oxides obtained decreased. This was attributed to the solid-solid interactions, which gave a new phase with lower catalytic activity than those of the interacting phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of the Acidic-basic Characters of Some Metal Oxides in the Pyrolysis of Ammonium Perchlorate

Six metal oxide samples were prepared by calcination of the corresponding precursors at 500°C for 5 h in air and were characterized by IR and XRD analyses. Their surface areas were calculated by means of the BET method. The acidities and basicities of these metal oxides were estimated thermogravimetrically by the method of adsorption of pyridine and formic acid as probe molecules. The pyrolyses of pure ammonium perchlorate (AP) and of AP mixed with (10% w/w) metal oxide were studied, in a dynamic atmosphere of N₂, by thermogravimetric analysis (TG) and derivative thermogravimetric analysis. A correlation was found between the catalytic activities of the metal oxides during the pyrolysis of AP, and their acidic-basic characters. The activation energies of the non-catalyzed and catalyzed pyrolysis of AP were calculated from the TG results via the Coats-Redfern equation. This revised version was published online in July 2006 with corrections to the Cover Date.