Oxidation of Aliphatic and Benzylic Alcohols by Oxone®, Catalysed by 12-Tungstocobaltate (II)

$R_1 R_2 CH_2 OH\xrightarrow[{50\% {\text{ }}Aqueous{\text{ }}acetonitrile}]{{[Co^{II} (W_{12} O_{40} )]^{6 - } /Oxone}}R_1 R_2 CHO$ A Keggin-type polyoxometalate (POM) 12-tungstocobaltate (II) ([Co^II(W₁₂O₄₀)]^6?) has been used as a catalyst for the oxidation of aliphatic and benzylic alcohols to the corresponding carbonyl compounds. The reduced (POM) formed in the oxidation of alcohols is re-oxidized by potassium peroxomonopersulphate.     

Site-Selective Pyridination of Benzylic and Allylic C−H bonds via Radical-Radical Cross-Coupling

Herein, we report a modular photocatalytic platform for the site-selective pyridination of saturated hydrocarbon compounds employing organic photoredox catalysis to forge new carbon-carbon bonds. The site-selective C−H pyridination could couple benzylic/allylic C−H bonds with pyridylphosphonium salts, which installed directly and regioselectively from C−H heteroarenes through a radical-radical cross coupling mechanism. This synthetic methodology could tolerate a variety of functional groups, complex heteroarenes, even late-stage functionalization of pharmaceuticals selectively.     

A Promiscuous Cytochrome P450 Hydroxylates Aliphatic and Aromatic C−H Bonds of Aromatic 2,5-Diketopiperazines

Cytochrome P450 enzymes generally functionalize inert C−H bonds, and thus, they are important biocatalysts for chemical synthesis. However, enzymes that catalyze both aliphatic and aromatic hydroxylation in the same biotransformation process have rarely been reported. A recent biochemical study demonstrated the P450 TxtC for the biosynthesis of herbicidal thaxtomins as the first example of this unique type of enzyme. Herein, the detailed characterization of substrate requirements and biocatalytic applications of TxtC are reported. The results reveal the importance of N-methylation of the thaxtomin diketopiperazine (DKP) core on enzyme reactions and demonstrate the tolerance of the enzyme to modifications on the indole and phenyl moieties of its substrates. Furthermore, hydroxylated, methylated, aromatic DKPs are synthesized through a biocatalytic route comprising TxtC and the promiscuous N-methyltransferase Amir_4628; thus providing a basis for the broad application of this unique P450.     

Four New Metal–Organic Supramolecular Networks Based on Aromatic Acid and Flexible Bis(imidazole) Ligand: Synthesis,Structures and Luminescent Properties

Four new metal–organic supramolecular networks, namely, [Zn(H₂pdc)₂(H₂O)₂]·2H₂O·bbi (1), {[Cd(Hpdc)₂]·2H₂O₂·H₂bbi}_n (2), [Zn(BA)₂(bbi)]_n (3), and {[Cd(BA)₂(bbi)]·H₂O}_n (4) (H₃pdc = 3,5-pyrazoledicarboxylic acid, HBA = 3-hydroxybenzoic acid and bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) have been synthesized under hydrothermal conditions and characterized by IR spectra, elemental analyses, and single-crystal X-ray diffraction analyses. Compound 1 possesses zero-dimensional (0D) structure, which is finally extended into a two-dimensional (2D) supramolecular network via O–H···O and C–H···O hydrogen bonds. Complex 2 displays a 2D network structure built from Cd²⁺ atoms interconnected by Hpdc^2? ligands. The adjacent networks are further assembled into three-dimensional (3D) supramolecular structure through O–H···O hydrogen bonds. Compounds 3 and 4 show similar one-dimensional (1D) chains, in which four-coordinated Zn(II) atoms and six-coordinated Cd(II) atoms are bridged by bbi ligands. Through O–H···O and C-H···O hydrogen bonding interactions, the 1D chains are further packed into 2D and 3D supramolecular frameworks for 3 and 4, respectively. Obviously, the structural differences among compelxes 1–4 are attributed to the different central metal atoms and organic ligands. In addition, compounds 1–4 exhibit blue fluorescent emission in the solid state at room temperature.     

From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling

It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca₄H₄Si₅O₁₆, Ca₂H₂Si₂O₇ and Ca₆(HSi₂O₇)₂(OH)₂, respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups via deprotonation and complexation with calcium. In the presence of Al in solution, the uptake of Al by C–S–H is experimentally observed. The Al content increases with Al concentration. C–A–S–H formation is modelled by the competition between silicate and aluminate tetrahedra for the bridging of the dimeric silicates in C–S–H.     

Sol–gel synthesis and characterization of lithium aluminate (L–A–H) and lithium aluminosilicate (L–A–S–H) gels

Hydrous lithium aluminosilicate (L–A–S–H) and lithium aluminate (L–A–H) gels are candidate precursors for glass-ceramics and ceramics with potential advantages over conventional processing routes. However, their structure before calcination remained largely unknown, despite the importance of precursor structure on the properties of the resulting materials. In the present study, it is demonstrated that L–A–S–H and L–A–H gels with Li/Al ≤ 1 can be produced via an organic steric entrapment route, while higher Li/Al ratios lead to crystallization of gibbsite or nordstrandite. The composition and the structure of the gels was studied by thermogravimetric analysis, X-ray diffraction, ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance, and Raman spectroscopy. Aluminium was found to be almost exclusively in six-fold coordination in both the L–A–H and the L–A–S–H gels. Silicon in the L–A–S–H gels was mainly in Q⁴ sites and to a lesser extent in Q³ sites (four-fold coordination with no Si–O–Al bonds). The results thus indicate that silica-rich and aluminium-rich domains formed in these gels.     

A vibrational study of the activation sequence of C–H and C–C bonds of isobutene and 1-butene on Mo(110) and (4 × 4)-C/Mo(110) surfaces

The thermal decomposition pathways of isobutene and 1-butene on both Mo(110) and 4 × 4-C/Mo(110) surfaces have been studied using high-resolution electron energy loss spectroscopy (HREELS) in order to highlight the substantially different activities of these two surfaces towards the cleavage of C–H and C–C bonds. On clean Mo(110), the CH₂ group of isobutene decomposes upon heating to 150 K, producing either a /-bonded isobutenylidene [(CH₃)₂CCH] species or a 1,1-di-/-bonded isobutenyl [(CH₃)₂CC] species. Upon further heating, extensive C–H bond scission occurs to form hydrocarbon fragments which do not contain CH₃ or CH₂ groups, but appear to have largely intact carbon skeletons. By contrast, isobutene is molecularly adsorbed on the carbide-modified surface at 150 K. Further heating produces isobutylidyne [(CH₃)₂HCC] by 300 K, which subsequently decomposes via C–C bond scission to generate surface methyl groups. The different activation sequence of the C–H and C–C bonds of isobutene on clean and carbide-modified Mo(110) surfaces is also qualitatively confirmed by comparative studies of 1-butene on the two surfaces.     

Carbonation of C–S–H and C–A–S–H samples studied by 13C, 27Al and 29Si MAS NMR spectroscopy

Synthesized calcium silicate hydrate (C–S–H) samples with Ca/Si ratios of 0.66, 1.0, and 1.5 have been exposed to atmospheric CO₂ at room temperature and high relative humidity and studied after one to 12 weeks. ²⁹Si NMR reveals that the decomposition of C–S–H caused by carbonation involves two steps and that the decomposition rate decreases with increasing Ca/Si ratio. The first step is a gradual decalcification of the C–S–H where calcium is removed from the interlayer and defect sites in the silicate chains until Ca/Si = 0.67 is reached, ideally corresponding to infinite silicate chains. In the seconds step, calcium from the principal layers is consumed, resulting in the final decomposition of the C–S–H and the formation of an amorphous silica phase composed of Q³ and Q⁴ silicate tetrahedra. The amount of solid carbonates and of carbonate ions in a hydrous environment increases with increasing Ca/Si ratio for the C–S–H, as shown by ¹³C NMR. For C–A–S–H samples with Ca/Si = 1.0 and 1.5, ²⁷Al NMR demonstrates that all aluminium sites associated with the C–S–H are consumed during the carbonation reactions and incorporated mainly as tetrahedral Al(–OSi)₄ units in the amorphous silica phase. A small amount of penta-coordinated Al sites has also been identified in the silica phase.     

Co and Fe Catalysed Fischer–Tropsch Synthesis in Biofuel Production

Synthesis of liquid biofuels from synthesis gas is considered. A series of Co, Co/Ru and Fe catalysts supported by three Al₂O₃ based supports were prepared and tested for the Fischer–Tropsch (FT) reaction. The effects of supports and precursor salts on the activity of the catalysts were studied in the hydrogenation of CO using H₂/CO in a ratio of 2:1. The most active catalysts were tested with gas mixture having a composition close to synthesis gas derived by gasification of biomass. The combination of precursor salt and support is significant in order to get an active catalyst. Cobalt-based catalysts with traces of ruthenium on a small particle support proved to be the most active in the production of hydrocarbons with FT reaction.     

Aromatic–aromatic interaction between metallacycle and phenyl ring

The X-ray crystal structure of [CuL₂]ClO₄ where L is the 1:1 condensate of benzil-monohydrazone and 2-pyridinecarboxaldehyde, reveals unprecedented π–π interaction between the metallacycles and phenyl rings. The interaction is intramolecular.     

Ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide and (Hf–Ta–Zr–Nb–Ti)C–xSiC composites

The ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide (HEC-0) was investigated using a plasma flame in air for different times (60, 90, and 120 s) at about 2100°C. The effect of SiC content on the ablation resistance of HEC–xSiC composites (x = 10 and 20 vol%) was also studied. The linear ablation rate of HEC-0 decreases with increasing ablation time, showing the positive role of the oxide layer with a complex composition. The linear ablation rate of HEC–10 vol% SiC (0.3 µm s⁻¹) is only a 10th of that of HEC-0, showing a significant improvement in ablation resistance, probably due to the formation of a protective oxide layer containing melted SiO₂ and refractory Hf–Zr–Si–O oxides.     

Iodine‐Mediated Synthesis of Aromatic Thioethers with Aromatic Amines and Sulfonyl Hydrazides in High Regioselectivity via C(sp2)?H Bond Functionalization

An iodine‐mediated synthesis of aromatic thioethers from aromatic amines and sulfonyl hydrazides via C(sp²) H bond functionalization and C S bond formation has been developed. In this procedure, various substituents on the sulfonyl hydrazides, such as alkyl, methoxyl, chloro, bromo and fluoro groups, and aromatic amines are tolerated in the thiolation which generates the desired products in moderate to good yields.

     

Synthesis and Structural Characterization of Novel Nanostructured Aromatic Optically Active Poly(Ester–Amide)s Derived from S-tyrosine Containing Symmetric Diol and Aromatic Diacid Chlorides

In this study, at first N,N′-bis[2-(methyl-3-(4-hydroxyphenyl)propanoate)]terephthaldiamide, as a new chiral monomer based on tyrosine amino acid, was synthesized from the reaction of S-tyrosine methyl ester and terephthaloyl dichloride. Then novel nanostructured aromatic optically active and eco-friendly poly(ester–amide)s based on tyrosine amino acid were synthesized by the solution polycondensation of the new diol and a number of aromatic diacid chlorides. The resulting poly(ester–amide)s exhibited good yields, solubility, inherent viscosities, and thermal stability. All polymers were characterized by Fourier transform infrared, ¹H NMR, elemental analysis, and specific rotation. They were also studied by X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy.     

异丁醛(IBA)的合成

甲醇与乙醇或正丙醇一步合成异丁醛,甲醇与正丙醇反应,催化剂为负载钒的TiO2,反应的转化率能够达到98.9%,异丁醛的产率可达64.2%。甲醇与乙醇反应,催化剂分别为V2O5/TiO2-SiO2,CuO-ZnO/Al2O3,CuO-MnO/Al2O3时,反应的转化率分别能达98%、93.1%、93.69%,异丁醛的选择性分别能达85%、53.1%、71%。     

Surface stabilities of 3C–SiC and H2O adsorption on the (110) surface

First-principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H₂O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C-poor condition, the nonstoichiometric Si-terminated (100) could become more energetically favored. The adsorption and dissociation of single H₂O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H₂O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top-most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H₂O, for a wide range of temperature and the partial potential of H₂O.