Tunable Synthesis of Monofluoroalkenes and Gem-Difluoroalkenes via Solvent-Controlled Rhodium-Catalyzed Arylation of 1-Bromo-2,2-difluoroethylene

Divergent synthesis of fluorine-containing scaffolds starting from a suite of raw materials is an intriguing topic. Herein, we report the solvent-controlled rhodium-catalyzed tunable arylation of 1-bromo-2,2-difluoroethylene. The selection of the reaction solvents provides switchable defluorinated or debrominated arylation from readily available feedstock resources (both arylboronic acids/esters and 1-bromo-2,2-difluoroethylene are commercially available). This switch is feasible because of the difference in coordination ability between the solvent (CH₂Cl₂ or CH₃CN) and the rhodium center, resulting in different olefin insertion. This protocol allows the convenient synthesis of monofluoroalkenes and gem-difluoroalkenes, both of which are important scaffolds in the fields of medicine and materials. Moreover, this newly developed solvent-regulated reaction system can be applied to the site-selective dechlorinated arylation of trichloroethylene. Overall, this study provides a useful strategy for the divergent synthesis of fluorine-containing scaffolds and provides insight into the importance of solvent selection in catalytic reactions.     

Highly Efficient and Chemoselective Tandem Hydroformylation-Hydrogenation of Alkenes to Alcohols over g-CN Supported Bimetallic Rh and Co Nanoparticles Catalysts

The objective of the tandem hydroformylation-hydrogenation of alkenes to corresponding alcohols was to design an efficient and stable heterogeneous catalyst. To this end, a series of novel heterogeneous graphitic carbon nitride (g-CN) supported bimetallic Rh−Co nanoparticle catalysts (Rh−Co/g-CN) were prepared and subsequently studied for this one-pot two-step reaction. The lamellar structure makes Rh and Co nanoparticles with diameters of <1 nm and 20 nm, respectively, homogeneously deposited on the surface of g-CN layers, exhibit remarkable conversion of styrene (99.9 %) and chemoselectivity for alcohol (87.8 %). More importantly, Co nanoparticles are found to play an important role in the improvement of the chemoselectivity for alcohol due to the formation of catalytic active species [HCo(CO)_y]. Besides the detailed investigation of the catalytic properties of Rh−Co/g-CN under different reaction conditions, the reuse of Rh−Co/g-CN was conducted for five times and no evident decrease in the activity and chemoselectivity was observed. Therefore, we expect that this work could offer an initial insight into g-CN-based heterogeneous catalyst on the tandem hydroformylation-hydrogenation reaction.     

Ag_3PO_4/Palygorskite的静电调控合成及可见光催化降解罗丹明B和气相异丙醇

以大比表面的廉价易得的凹凸棒(palygorskite)为载体,借助带电荷界面的静电调控作用,采用吸附-沉积沉淀方法制备磷酸银/凹凸棒(Ag3PO4/palygorskite)复合催化剂.利用X-射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、原子吸收光谱(AAS)、紫外可见漫反射光谱(UV-Vis DRS)等技术系统地表征催化剂.之所以能够制备高分散性的凹凸棒负载的磷酸银催化剂,主要是因为凹凸棒具有较大的比表面积、带负电荷界面以及适宜的磷酸根前驱体.以可见光催化脱色降解罗丹明B和氧化降解异丙醇为探针反应,考察复合材料的催化性能.研究表明,与纯磷酸银相比,磷酸银/凹凸棒催化脱色降解罗丹明B和氧化降解异丙醇速率分别提高了2和2.5倍.     

A DFT study of DMC formation on Rh‐doped Cu/AC surfaces

The activity and selectivity of heterogeneous catalysts can be significantly improved by dispersion of another active component in the metal substrate. The impact of Rh promoter on the formation of dimethyl carbonate (DMC) via oxidative carbonylation of methanol on Cu–Rh/AC (activated carbon) catalyst was investigated by density functional theory calculations. The most stable configurations of reacting species (CO, OH, CH₃O, monomethyl carbonate, and DMC) adsorbed on the Cu⁰(zero‐valent copper)/AC and Cu–Rh/AC surfaces were determined on the basis of the calculated results. The reaction energy and activation energy of the rate‐limiting steps on the Cu–Rh/AC and Cu⁰/AC surfaces were compared. The activation energies of the rate‐limiting step of CO insertion into dimethoxide are 206.3 and 304.8 kJ mol^?1 on the Cu–Rh/AC and Cu⁰/AC surfaces, respectively. The activation energies of the rate‐limiting step of CO insertion into methoxide are 78.5 and 92.7 kJ/mol on the Cu–Rh/AC and Cu⁰/AC surfaces, respectively. The calculated results indicate that the addition of Rh atom has a significant effect on decreasing the active energy the main pathway for DMC formation. © 2015 Wiley Periodicals, Inc.     

Rh(III)-catalyzed annulation of azobenzenes and α-Cl ketones toward 3-acyl-2H-indazoles

Rhodium(III)-catalyzed [4 + 1] cyclization of azobenzenes with α-Cl ketones has been developed. 3-Acyl-2H-indazoles could be easily afforded in up to 97% yields for more than 30 examples. The obtained products are potentially valuable in organic synthesis and drug discovery. This protocol featured with high efficiency, extensive functional group tolerance and mild reaction conditions. The one-step efficient construction of an anti-inflammatory agent confirms the practicability of this procedure.     

通过"双离子键"固载于季鏻盐聚合物的[Rh(CO)I3]2–物种在多相乙醇羰基化中的应用

贵金属物种(Rh或Ir络合物)在均相羰基化和氢甲酰化催化过程得到了广泛的应用,但始终存在分离繁琐等问题,其均相多相化可很大程度上简化分离操作,故一直广受重视.单位点催化剂因其具有可与均相相比拟的较高金属利用率和选择性而成为均相多相化的重要研究方向之一.研究发现,在碘物种存在的情况下用于固载金属物种的配位键容易断裂,进而导致金属物种的流失,而通过离子键固载的[Rh(CO)₂I₂]^–物种更加稳定,比如著名的甲醇羰基化“Acetica^TM”工艺中,[Rh(CO)₂I₂]^–负一价阴离子物种是以离子键的方式固定在带有阳离子骨架的甲基化聚乙烯吡啶树脂上.与甲醇羰基化过程类似的乙醇羰基化过程是生产重要化工中间体丙酸的主要途径之一,但该过程的均相多相化始终存在着稳定性差这一关键问题.为了解决这一问题,基于之前将固载于季鏻盐聚合物的[Rh(CO)I₃]^2–应用于甲醇羰基化的工作,我们将类似的季鏻盐聚合物固载Rh基催化剂Rh-TPISP用于多相乙醇羰基化过程,通过多种表征进一步证明了Rh物种和P物种结构,并提出了“双离子键”模型.P的K边XANES证明了聚合物TPISP的季鏻化阳离子骨架特征.HAADF-STEM测试表明Rh-TPISP中的Rh呈现单位点分散的状态.Rh的XPS和XANES结果证明了Rh-TPISP中Rh物种的价态介于0~+1.通过EXAFS的拟合解析给出了[Rh(CO)I₃]^2–活性中心结构.由于[Rh(CO)₂I₂]^–为经典的羰基化活性中心,为了进一步证明该结构的正确性,我们将Rh-TPISP的EXAFS和IR谱图与标样[PPh3Et]⁺[Rh(CO)₂I₂]^–对比发现:在EXAFS谱图中,Rh-TPISP中的Rh-C峰高低于[PPh3Et]+[Rh(CO)₂I₂]^–的Rh-C峰高,而Rh-TPISP中的Rh-I峰高高于[PPh3Et]+[Rh(CO)₂I₂]^–的Rh-I峰高,这就说明Rh-TPISP中Rh物种的Rh-C配位数小于2,而Rh-I配位数大于2;在IR谱图中,标样[PPh3Et]+[Rh(CO)₂I₂]^–中有两个羰基振动峰,与该物种的两个Rh-C配位键相符,而Rh-TPISP中的只有一个羰基振动峰,说明Rh-C配位数为1.因此,Rh-TPISP催化剂的季鏻盐骨架中的每个P物种带有一个正电荷,每个带有两个负电荷的[Rh(CO)I₃]^2–通过与两个[P]⁺的静电作用进行固载,形成“双离子键”结构.该催化剂在固定床乙醇羰基化过程中表现出优异的羰基化活性、选择性和稳定性.在3.5 MPa、195 oC反应近1000 h后,Rh-TPISP催化剂TOF保持在约350 h–1,丙酰基选择性为95%以上,高出所有文献报道的均相和多相乙醇羰基化活性.其较高的活性主要是因为[Rh(CO)I₃]^2–比传统Rh活性相[Rh(CO)₂I₂]^–具有更强的富电子性,而较高的稳定性主要是由于“双离子键”这种强静电作用比“AceticaTM”工艺中“单离子键”更有利于Rh物种的固载.故Rh-TPISP催化剂中的“双离子键”对其优异的催化性能具有极其重要的作用,对后续多相乙醇羰基化的发展具有重要意义.     

Synthesis and Structure of Bis(2-Amino-5-Cyanopyridinium) Diaquadichlorocopper(II) Dichloride

The reaction of CuCl₂ with 2-amino-5-cyanopyridine and HCl in 1-propanol gave bis(2-amino-5-cyanopyridinium) diaquadichlorocopper(II) dichloride (1). Crystal data for 1 are: monoclinic, space group: P2₁/c, a = 8.461(3) Å, b=14.665(5) Å, c=7.883(3) Å, g =96.105(4)°, V=972.6(6) Å 3 , Z=2, D_calc =1.645 Mg/m³, w =1.691 mm^?1, F(OOO)=486, MoK _f( u =0.71073 Å), R1=0.0431 for [∣I∣ S 2 σ (I)] and R1=0.0680 for all 1944 unique reflections and 130 parameters. The structure exists as square planar Cu(H₂O)₂Cl₂ units with long semi-coordinate bonds to the cyano nitrogens of the 2-amino-5-cyanopyridinium ions. Hydrogen bonding from the water molecules and N―H hydrogens to the chloride irons stablises the lattice.     

Irreversible helix rearrangement from Cis‐transoid to Cis‐cisoid in poly(p‐n‐hexyloxyphenylacetylene) induced by heat‐treatment in solid phase

Polymerization of p‐n‐hexyloxyphenylacetylene (pHPA) by using a [Rh(norbornadine)Cl]₂‐triethylamine catalyst was carried out at room temperature to afford stereoregular helical poly(p‐n‐hexyloxyphenylacetylene)s (PpHPAs). When ethanol and n‐hexane were used as polymerization solvents, a bright yellow PpHPAs, poly( Y ) with M_n = 8.5 × 10⁴ and its purple red polymer, poly( R ) with M_n = 5.3 × 10⁴ were obtained in 95% yields and 84% yields, respectively. Diffuse reflective UV–vis spectra of poly( Y ) and poly( R ) in solid phase showed different broad absorption peaks at 445 and 575 nm, respectively. X‐Ray diffraction patterns of poly( Y ) and poly( R ) showed typical columnar structures assignable to cis‐transoid and cis‐cisoid structures, respectively, which were also supported by molecule mechanics calculation. Poly( Y ) was irreversibly transformed to a reddish‐black polymer, poly( Y‐B ), which columnar diameter was nearly the same as that of poly( R ). Further, poly( Y ) showed an exothermic peak in the differential scanning calorimetry trace at 80 °C for 1 h in N₂ gas. Thus, these findings suggest a thermally irreversible rearrangement from an unstable cis‐transoid form, poly( Y ) with a stretched cis‐transoid helix to a stable cis‐cisoid form, poly( R ), with a contracted cis‐cisoid helix in the solid phase to give poly( Y → B ) with the cis‐cisoid form. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Determination of Pd,Rh, Pt,Au in road dust by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporization (USS-ETV-ICP-MS) has been applied to determine Pd, Rh, Pt and Au in 0.5% m/v slurries of several road dust samples. 2% m/v ammonium pyrrolidine dithiocarbamate (APDC) was used as the modifier to enhance the ion count. The influence of instrument operating conditions, slurry preparation and interferences on the ion count was reported. This method has been applied to the determination of Pd, Rh, Pt and Au in BCR 723 Road Dust and NIST SRM 2709 San Joaquin Soil reference materials and two road dust samples collected locally. The analysis results of the standard reference materials agreed with the certified values. Precision between sample replicates was better than 10% for all the determinations. The method detection limits estimated from standard addition curves were 0.9, 0.4, 0.6 and 0.4 ng g⁻¹ for Pd, Rh, Pt and Au, respectively, in original dust samples.     

具有优异甲醇耐受性的Rh掺杂PdCu有序金属间化合物纳米粒子增强氧还原电催化

Direct methanol fuel cells (DMFCs), as one of the important energy conversion devices, are of great interest in the fields of energy, catalysis and materials. However, the application of DMFCs is presently challenged because of the limited activity and durability of cathode catalysts as well as the poisoning issues caused by methanol permeation to the cathode during operation. Herein, we report a new class of Rh-doped PdCu nanoparticles (NPs) with ordered intermetallic structure for enhancing the activity and durability of the cathode for oxygen reduction reaction (ORR) and achieving superior methanol tolerance. The disordered Rh-doped PdCu NPs can be prepared via a simple wet-chemical method, followed by annealing to convert it to ordered phases. The results of transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), power X-ray diffraction (PXRD) analysis and high resolution TEM (HRTEM) successfully demonstrate the formation of near-spherical NPs with an average size of 6.5 ± 0.5 nm and the conversion of the phase structure. The complete phase transition temperatures of Rh-doped PdCu NPs and PdCu are 500 and 400 ℃, respectively. The molar ratio of Rh/Pd/Cu in the as-synthesized Rh-doped PdCu NPs is 5/48/47. Benefitting from Rh doping and the presence of the ordered intermetallic structure, the Rh-doped PdCu intermetallic electrocatalyst achieves the maximum ORR mass activity of 0.96 A·mg^-1 at 0.9 V versus reversible hydrogen electrode (RHE) under alkaline conditions—a 7.4-fold enhancement compared to the commercial Pt/C catalyst. For different electrocatalysts, the ORR activities follow the sequence, ordered Rh-doped PdCu intermetallics > ordered PdCu intermetallics > disordered Rh-doped PdCu NPs > disordered PdCu NPs > commercial Pt/C catalyst. In addition, the distinct structure endows the Rh-doped PdCu intermetallics with highly stable ORR durability with unaltered half-wave potential (E_1/2) and mass activity after continuous 20000 cycles, which are higher than those of other electrocatalysts. Furthermore, the E_1/2 of the Rh-doped PdCu intermetallics decreases by only 5 mV after adding 0.5 mol·L^-1 methanol to the electrolyte, while the commercial Pt/C catalyst negatively shifts by 235 mV and a distinct oxidation peak can be observed. The results indicate that the ORR activity of the Rh-doped PdCu intermetallic electrocatalyst can be well maintained even in the presence of poisoning environment. Our results have demonstrated that Rh-doped PdCu NPs with ordered intermetallic structures is a potential electrocatalyst toward the next-generation high-performance DMFCs.