Direct synthesis of (η-arene)-tricarbonylchromium complexes by arene displacement from tricarbonyl(η-1-methylpyrrole)chromium(0)

Arene displacement from the title complex occurs under unprecedented mild conditions in neutral media to afford (η⁶-arene)tricarbonylchromium complexes. The process is most effective with heteroaromatic compounds: the first synthesis of a tricarbonyl(η⁶-quinoline)chromium complex and the diastereoselective preparation of a (η⁶-indole) complex derived from L-tryptophan are reported as representative examples.     

Kinetic Spectrophotometric Determination of Chromium (VI) by Oxidation of Sodium Pyrogallol-5-sulphonate by Hydrogen Peroxide

Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H₂O₂. The optimum reaction conditions are PS (1.32·10^–3mol·dm^–3), H₂O₂ (0.32mol·dm^–3), HClO₄ (2.6·10^–3mol·dm^–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm^–3 and a detection limit of 0.024ng·cm^–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples.     

Density functional calculations of the structures and bond energies of Cr(CO)6 and (η6-C6H6) Cr(CO)2(CX) (X=O,S) complexes

Summary Quantum chemical calculations based on density functional theory have been performed on Cr(CO)₆, (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) at the local and nonlocal level of theory using different functionals. Good agreement is obtained with experiment for both optimized geometries and metal-ligand binding energies. In particular, a comparison of metal-arene bond energies calculated for the (⁶-C₆H₆)Cr(CO)₃ and (⁶-C₆H₆)Cr(CO)₂(CS) complexes correlates well with kinetic data demonstrating that substitution of one CO group by CS leads to an important labilizing effect of this bond, which may be primarily attributed to a larger -backbonding charge transfer to the CS ligand as compared with CO.     

铬系乙烯齐聚和聚合催化剂

综述了近年来国内外铬系催化剂的最新研究进展。介绍了该类催化剂齐聚和合的性能研究和应用，讨论了该催化剂长期引起争议的活性中心，活性价态，以及反应机理，并同时预测了铬系催化剂在工业和纳米技术方面的发展趋势。     

Beiträge zum thermischen Verhalten wasserfreier Phosphate. IX. Darstellung und Kristallstruktur von Cr6(P2O7)4. Ein gemischtvalentes Pyrophosphat mit zwei- und dreiwertigem Chrom

Contributions on the Thermal Behaviour of Anhydrous Phosphates. IX. Synthesis and Crystal Structure of Cr₆(P₂O₇)₄. A Pyrophosphate Containing Di- and Trivalent Chromium Cr₆(P₂O₇)₄ (Cr₂²⁺Cr₄³⁺(P₂O₇)₄) can be obtained reducing CrPO₄ by phosphorus (950°C, 48 h, 100 mg iodine as mineralizer). By means of chemical transport reactions (transport agent iodine; 1050 → 950°C) the compound has been separated from its neighbour phases (Cr₂P₂O₇, CrP₃O₉) and crystallized (greenish, transparent crystals; edge length up to 0.3 mm). The crystal structure of Cr₆(P₂O₇)₄ (Spcgrp.: P-1; z = 1; a = 4.7128(8) Å, b = 12.667(3) Å, c = 7.843(2) Å, α = 89.65(2)°, β = 92.02(2)°, γ = 90.37(2) has been solved and refined from single crystal data (2713 unique reflections, 194 parameter, R = 0.035). Cr²⁺ is surrounded by six oxygen atoms which occupy the corners of an elongated octahedron (4 × d^{Cr? O} ≈? 2.04 Å; 2 × d^{Cr? O} ≈? 2.62 Å). The Cr³⁺ ions are also coordinated octahedraly (1.930 Å ≤ d_{Cr? O} ≤ 2.061 Å). The crystallographically independent pyrophosphate groups show nearly eclipsed conformation. The bridging angles (P? O? P) are 136.5° and 138.9° respectively.     

Enantioselective allylation of alkyl glyoxylates catalyzed by (salen)chromium(III) complexes

The enantioselective addition of allylstannanes and allylsilanes to alkyl glyoxylates of type 1, catalyzed by chiral (salen)Cr(III) complexes 3, has been studied. We have found that the reaction proceeded smoothly for low loading (1-2 mol %) of (1R,2R)-(salen)Cr(III)BF₄3a or (1R,2R)-(salen)Cr(III)ClO₄3c, and allyltributyltin under simple, undemanding conditions, affording (R)-2-hydroxypent-4-enoic acid esters 2 in good yield (61-90%) and enantioselectivity (58-76% ee).     

Elimination of SAS Interferences in Catalytic Adsorptive Stripping Voltammetric Determination of Cr(VI) by Means of Fumed Silica

In the work the procedure of chromium(VI) determination by catalytic adsorptive stripping voltammetry (CAdSV) with application of fumed silica, is presented. Two variants of the method are proposed: in the first fumed silica is put directly to the electrolytic cell containing tested solution, in the second the silica is shaken with the sample and next centrifuged. The effectiveness of many surface‐active substances removal from synthetic solutions as well as natural water samples, is studied. In the experiments the fumed silica (Sigma‐Aldrich) of the specific surface area in the range 200–390 m² g^?1 was used. Two types of the working electrodes were applied, i.e., hanging mercury drop electrode (HMDE) and cyclic renewable mercury film electrode (Hg(Ag)FE). In the silica presence i) the relative standard deviation (RSD) for 0.1 μg L^?1 Cr(VI) is <2% (HMDE) and <5% (Hg(Ag)FE), n=7, ii) the detection limits estimated deposition time 20 s were respectively 14 ng L^?1 (HMDE) and 22 ng L^?1 (Hg(Ag)FE). The accuracy of the method was tested by studying the recovery of Cr(VI) from spiked natural water samples.     

Rhodium(I) catalyzed four-component reaction of Fischer alkenyl carbene complexes and 1,1-diphenylallene

Alkyl substituted chromium Fischer carbene complexes react with 1,1-diphenylallene in the presence of rhodium(I) catalysts (10 mol%) to yield highly substituted dienyl indenone derivatives. In this process a catalytic chromium(0)-rhodium(I) exchange occurs, four new C-C bonds are created, and four-components (two allenes, the carbene ligand and one CO ligand) are joined in a chemo- and regioselective manner.     

Room temperature photoluminescence of amorphous BaxSr1−xTiO3 doped with chromium

ABO₃ amorphous materials, such as BaTiO₃ (BT), SrTiO₃ (ST), PbTiO₃ (PT), and Ba_xSr_1−xTiO₃ (BST) have recently attracted a good deal of attention due to their ferroelectric and electro-optical properties. Intense photoluminescence at room temperature was observed in amorphous titanate doped with chromium (Ba_xSr_1−xTi_1−yCr_yO₃) prepared by the polymeric precursor method. Results indicated that substantial luminescence at room temperature was achieved with the addition of small Cr contents to amorphous Ba_xSr_1−xTi_1−yCr_yO₃. Further addition of Cr or crystallization were deleterious to the intensity of the luminescent peak obtained for excitation using λ=488.0 nm.     

Ternary silicides M2Cr4Si5 (M=Ti, Zr, Hf): filled variants of the Ta4SiTe4 structure type

The isostructural ternary silicides M₂Cr₄Si₅ (M=Ti, Zr, Hf) were prepared by arc-melting of the elemental components. The single-crystal structure of Zr₂Cr₄Si₅ was determined by X-ray diffraction (Pearson symbol oI44, orthorhombic, space group Ibam, Z=4, a=7.6354(12) Å, b=16.125(3) Å, c=5.0008(8) Å). Zr₂Cr₄Si₅ adopts the Nb₂Cr₄Si₅-type structure, an ordered variant of the V₆Si₅-type structure. It consists of square antiprisms that have Zr and Cr atoms at the corners and Si atoms at the centers; they share opposite faces to form one-dimensional chains _∞¹[Zr_4/2Cr_4/2Si] surrounded by additional Si atoms and extending along the c direction. In a new interpretation of the structure, additional Cr atoms occupy interstitial octahedral sites between these chains, clarifying the relation between this structure and that of Ta₄SiTe₄. The formation of short Si-Si bonds in Zr₂Cr₄Si₅ is contrasted with the absence of Te-Te bonds in Ta₄SiTe₄. The compounds M₂Cr₄Si₅ (M=Ti, Zr, Hf) exhibit metallic behavior and essentially temperature-independent paramagnetism. Bonding interactions were analyzed by band structure calculations, which confirm the importance of Si-Si bonding in these metal-rich compounds.