Clusterkomplexe [M2Rh(μ‐PCy2)(μ‐CO)2(CO)8] mit triangularem Metallgerüst RhM2 (M = Mn,Re; M2 = MnRe): Synthese,Struktur, Ringöffnungen und Katalysatoreigenschaften für die Isomerisierung und Hydroformylierung von 1‐Hexen

Cluster Complexes [M₂Rh(μ‐PCy₂)(μ‐CO)₂(CO)₈] with Triangular Core of RhM₂ (M = Re, Mn; M₂ = MnRe): Synthesis, Structure, Ring Opening Reaction, and Properties as Catalysts for Hydroformylation and Isomerisation of 1‐Hexene The salts PPh₄[M₂(μ‐H)(μ‐PCy₂)(CO)₈] and Rh(COD)[ClO₄] were in equimolar amounts reacted at –40 to –15 °C in the presence of CO_(g) in CH₂Cl₂/methanol solution under release of PPh₄[ClO₄] to intermediates. Such species formed in a selective reaction the unifold unsaturated 46 valence electrons title compounds [M₂Rh(μ‐PCy₂)(μ‐CO)₂(CO)₈] (M = Re 1 , Mn 2 ; M₂ = MnRe 3 ) in yields of > 90%; analogeous the derivatives with the PPh₂ bridge could the obtained (M = Re 4 , Mn 5 ). From these clusters the molecular structure of 2 was determined by a single crystal X‐ray analysis. The exchange of the labil CO ligand attached at the rhodium ring atom in 1 – 3 against selected tertiary and secondary phosphanes in solution gave the substitution products [M₂RhL(μ‐PCy₂)(μ‐CO)₂(CO)₇] (M = Re: L = PMe₃ 6 , P(n‐Bu)₃ 7 , P(n‐C₆H₄SO₃Na)₃ 8 , HPCy₂ 9 , HPPh₂ 10 , HPMen₂ 11 , M₂ = MnRe: L = HPCy₂ 12 ) nearly quantitative. Such dimanganese rhodium intermediates ligated with secondary phosphanes were converted in a subsequent reaction to the ring‐opened complexes [MnRh(μ‐PCy₂)(μ‐H)(CO)₅Mn(μ‐PR₂)(CO)₄] (M = Mn: R = Cy 13 , Ph 14 , Mn 15 ). The molecular structure of 13 , which showed in the time scale of the ³¹P NMR method a fluxional behaviour, was determined by X‐ray structure analysis. All products obtained were always characterized by means of υ(CO)Ir, ¹H and ³¹P NMR measurements. From the reactants of hydroformylation process, CO_(g) 1 – 2 in different solvents afforded at 20 °C under a reversible ring opening reaction the valence‐saturated complexes [MRh(μ‐PCy₂)(CO)₇M(CO)₅] (M = Re 16 , Mn 17 ), whereas the reaction of CO_(g) and the ring‐opened 13 to [MnRh(μ‐PCy₂)(μ‐H)(CO)₆Mn(μ‐PCy₂)(CO)₄] ( 18 ) was as well reversible. The molecular structures of 17 and 18 were determined by X‐ray analysis. The υ(CO)IR, ¹H and ³¹P NMR measurements in pressure‐resistant reaction vessels at 20 °C ascertained the heterolytic splitting of hydrogen in the reaction of 1 – 2 dissolved in CDCl₃ or THF‐d₈ under formation of product monoanions [M₂Rh(μ‐CO)(μ‐H)(μ‐PCy₂)(CO)₉]^– (M = Re, Mn), which also were formed by the reaction of NaBH₄ and 1 – 2 . Finally, the substrate 1‐hexene and 1 and 3 gave under the release of the labil CO ligand an η²‐coordination pattern of hexene, which was weekened going from the Re to the Mn neighbor atoms. After the results of the catalytic experiments with 1 and 2 as catalysts, such change in the bonding property revealed an advantageous formation of hydroformylation products for the dirhenium rhodium catalyst 1 and that of isomerisation products of hexene for the dimanganese rhodium catalyst 2 . Par example, 1 generated n‐heptanal/2‐methylhexanal in TOF values of 246 [h^–1] (n/iso = 3.4) and the c,t‐hexenes in that of 241 [h^–1]. Opposotite to this, 2 achieved such values of 55 [h^–1] (n/iso = 3.6) and 473 [h^–1]. A triphenylphosphane substitution product of 1 increased the activity of the hydroformylation reaction about 20%, accompanied by an only gradually improved selectivity. The hydrogenation products like alcohols and saturated hydrocarbons known from industrial hydroformylation processes were not observed. The metals manganese and rhenium bound at the rhodium reaction center showed a cooperative effect.     

Selective CO2-to-Syngas Conversion Enabled by Bimetallic Gold/Zinc Sites in Partially Reduced Gold/Zinc Oxide Arrays

Electrocatalytic CO₂-to-syngas (gaseous mixture of CO and H₂) is a promising way to curb excessive CO₂ emission and the greenhouse gas effect. Herein, we present a bimetallic AuZn@ZnO (AuZn/ZnO) catalyst with high efficiency and durability for the electrocatalytic reduction of CO₂ and H₂O, which enables a high Faradaic efficiency of 66.4 % for CO and 26.5 % for H₂ and 3 h stability of CO₂-to-syngas at −0.9 V vs. the reversible hydrogen electrode (RHE). The CO/H₂ ratios show a wide range from 0.25 to 2.50 over a narrow potential window (−0.7 V to −1.1 V vs. RHE). In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy combined with density functional theory calculations reveals that the bimetallic synergistic effect between Au and Zn sites lowers the activation energy barrier of CO₂ molecules and facilitates electronic transfer, further highlighting the potential to control CO/H₂ ratios for efficient syngas production using the coexisting Au sites and Zn sites.     

Rapid Screening of Olefin Polymerization Catalyst Libraries by Electrospray Ionization Tandem Mass Spectrometry

The simultaneous screening of catalysts according to their propensity for catalyzing the polymerization of ethylene (see scheme) can be achieved with the help of electrospray ionization tandem mass spectrometry. A small (eight catalysts) library of Pd^II complexes synthesized simultaneously in a one-pot reaction has demonstrated the efficiency of this new screening technique. This method could be widened to libraries of other olefin polymerization catalysts.     

Synthesis of 3-(quinoxalin-2-yl)-2H-chromen-2-ones under microwave irradiation

Abstract  A facile procedure for the synthesis of quinoxalines is being reported starting from 3-(2-bromoacetyl)coumarins or 3-(2-bromobutanoyl)coumarins and substituted o-phenylenediamines. The reactions were carried out under catalyst-free and microwave irradiation conditions producing the title compounds in moderate to excellent yields in a short time with easy workup. The structures of all new compounds have been confirmed on the basis of their IR, ¹H NMR, ¹³C NMR, and HRMS data. Graphical Abstract        

On the structure and cure acceleration of phenol-urea-formaldehyde resins with different catalysts

Phenol-urea-formaldehyde (PUF) resins with different catalysts [calcium oxide (CaO), sodium carbonate (Na₂CO₃), zinc oxide (ZnO), and magnesium oxide (MgO)] were prepared to accelerate the cure of the resin at low temperature. The cure-acceleration effects of catalysts on chemical structure and cure characteristics of PUF resins were investigated by using both liquid ¹³C nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The liquid ¹³C NMR analysis indicated that the catalyst such as CaO seemed to present a retarded effect on the polycondensation reaction of phenolic components with urea units, while the Na₂CO₃ appeared to promote the self-condensation reaction of phenolic methylol groups at para position toward the formation of para-para methylene linkage. Both ZnO and MgO in PUF resins promoted self-condensation reaction of para methylol groups and condensation reaction of ortho methylol groups with para methylol groups. The catalysts such as Na₂CO₃, ZnO, and MgO can make PUF resins cure at a low temperature. Among these catalysts, the MgO had the most significant accelerating effect on polycondensation and cure reaction of PUF resin.     

Diruthenium(I,I) saccharinate complexes: Synthesis, molecular structure, and evaluation as catalysts for carbenoid reactions of diazoacetates

The dinuclear ruthenium complexes [Ru₂(μ-sac)₂(CO)₆] (1), [Ru₂(μ-sac)₂(CH₃CN)₂(CO)₄] (3), [Ru₂(μ-sac)₂(CO)₅(PPh₃)] (4) and [Ru₂(μ-sac)₂(CO)₄(PPh₃)₂] (5) as well as the tetranuclear ruthenium complex [Ru₂(μ-sac)₂(CO)₅]₂ (2) (sac = saccharinate, C₇H₄NO₃S⁻) were synthesized starting from Ru₃(CO)₁₂ and saccharin. X-ray crystal structure analysis of 1, 3A × p-xylene, 4 × CH₂Cl₂ and 5 × 3CH₂Cl₂ showed that the core is bridged through the amidate moieties of the two saccharinate ligands, with a head-tail arrangement in complexes 1, 3A and 5, and a head-head arrangement in 4. For complex 3, an equilibrium mixture of the head-head regioisomer 3A and a second species 3b exists in solution. Complexes 1 and 2 are suitable catalysts for the cyclopropanation of nucleophilic alkenes (styrene, cyclohexene and 2-methyl-2-butene) with methyl diazoacetate.     

Isonitroso-4-Methyl-2-Pentanone for Solvent Extraction and Spectrophotometric Determination of Palladium (II) at Trace Level

Abstract

Isonitroso-4-methyl-2-pentanone (HIMP) is proposed as a new reagent for extraction and photometric determination of Pd(II). The reagent forms a yellow complex with palladium in the pH range 4.0-5.0. The complex extracted into chloroform was measured at 330 nm. The molar absorptivity was found to be 5.37 × 10³ 1 mol^?1 cm^?1 and Sandell's sensitivity 20 ng cm^?2 Beer's law was obeyed over the concentration range 0.1-10.0 μg/ml of palladium. The method is applicable for palladium estimation in Ores and catalysts.     

Hydrogen Peroxide Oxidation of Hydrocarbons Catalyzed by a Silica Supported Iron Precursor

Summary.  Silica supported iron(II) was found to be an efficient catalyst for oxidation of hydrocarbons with hydrogen peroxide. Received January 29, 2001. Accepted (revised) March 5, 2001     

Base-free anaerobic Cu(II) catalysed aryl-nitrogen bond formations

The coupling of arylboronic acids with imidazole in the presence of binuclear bis-μ-hydroxy copper(II) complexes is reported. The reactions can be performed in air as well as under nitrogen atmosphere. Reactions are carried out at ambient temperature without the need for base. The presence of water is essential for the reaction to proceed. Ligand effects on the yield and selectivity are reported.     

LaMnyCo1-yO3催化剂中氧状态的XPS研究

钙铁石型稀土复合氧化物因其结构和性能的多样性，作为重要的功能材料（超导体、电极材料、光学材料、催化剂等）受到普遍重视[1]ABO3型稀土复合氧化物热稳定性高·文献[2-4]曾报导了La1－xCexCoO3、La1－xAx－Mno。、Lal。Sr。CoO。催化剂体系A位离子的偏析、价态和氧的非化学计量问题．本文是保持A位离子La不变，B位离子由Mn、Co组成的体系，通过B位离子组合来讨论过渡金属离子的电子组态导致氧状态变化对催化性能的影响．1实验部分（1）试剂：La（NO3h、Mn（NO3h、Co（NO小分析结（2）催化剂制备：按化学计量比混合溶液，用…