Catalytic Condensation of Primary Amines, Dehydrogenation of Secondary Amines, and Dealkylation of Tertiary Amines over Solid-State Rhenium Sulfide Clusters with an Octahedral Metal Framework

When solid-state rhenium sulfide clusters with an octahedral metal framework are treated in a hydrogen stream above 300 °C, a catalytic activity for condensation of butylamine to yield N-butylidenebutylamine develops. Primary amines such as ethylamine, pentylamine, and hexylamine are also converted to the corresponding N-alkylidenealkylamines. Secondary amines such as diethylamine, dipropylamine, and dibutylamine are dehydrogenated to the corresponding N-alkylidenealkylamines. When triethylamine is allowed to react, dealkylation proceeds to yield diethylamine and its dehydrogenated product N-ethylideneethylamine. Trimethylamine is also dealkylated to dimethylamine. This series of catalytic behavior is the same as that of palladium and platinum metals. The similarity in selectivity is attributable to the rhenium atom that accepts electrons from the sulfur ligands leading to isoelectronic with the platinum group metals.     

Preparation, Characterization and Catalysis of Intrazeolite Molybdenum, Cobalt and Cobalt–Molybdenum Sulfide Clusters: A Molecular Approach to Hydrodesulfurization Catalysts

Better understandings of the nature of Co–Mo sulfide catalysts are of great importance to a rational design of highly active hydrodesulfurization catalysts on a molecular level. Synthesis of uniform binary sulfide clusters well-defined in structure and thermally stabilized on a support is desirable for such purposes. In the present study, successful preparations, using metal carbonyls as precursors, of Mo, Co and Co–Mo sulfide clusters encaged in zeolite are reported. The structure, location and catalytic properties of the clusters are described on the basis of XPS, XAFS, XRD, XRF, IR, HREM and adsorptions of benzene and NO. Implications for the generation of catalytic synergy between Co and Mo sulfides are presented in brief. It is suggested that the host–guest interactions between zeolite framework oxygens and precursor molecules and product clusters are crucial to the size and structure of the intrazeolite clusters.     

Thermal Activation of Molecular Tungsten Halide Clusters with the Retention of an Octahedral Metal Framework and the Catalytic Dehydration of Alcohols to Olefins as a Solid Acid Catalyst

When the molecular tungsten halide cluster (H₃O)₂[(W₆Cl₈)Cl₆]·6H₂O, with an octahedral metal framework, is heated to 50 and 150 °C in flowing helium gas, it changes into (H₃O)₂[(W₆Cl₈)Cl₆] and [(W₆Cl₈)Cl₄(H₂O)₂], respectively. Activation at 250 °C yields a poorly crystallized solid state cluster, [W₆Cl₈]Cl₂Cl_4/2, which exhibits catalytic activity for the dehydration of ethanol to yield ethylene and a small amount of ethyl ether and acetal. The activity is attributed to the Br?nsted acidity of the hydroxo ligand that is produced by elimination of hydrogen chloride from the chloro and aqua ligands. The catalytic activity increases with increasing temperature, and reaches a maximum at 300 °C. The catalytic activity then disappears above 350 °C, at which temperature the crystallinity of the cluster improves and the active sites are included in the crystal. In the case of primary alcohols, the reactivity decreases with increasing length of the carbon chain, and secondary alcohols are more reactive than the corresponding primary alcohols. Halide clusters of niobium, molybdenum, and tantalum having the same metal framework are also active catalysts for these reactions.     

Gas Phase Ion Chemistry of Transition Metal Clusters: Production, Reactivity, and Catalysis

This review focuses on the use of mass spectrometry to examine the gas phase ion chemistry of metal clusters. Ways of forming gas phase clusters are briefly overviewed and then the gas phase chemistry of silver clusters is discussed to illustrate the concepts of magic numbers and how reactivity can be size dependent. The chemistry of other bare and ligated metal clusters is examined, including mixed metal dimer ions as models for microalloys. Metal clusters that catalyze gas phase chemical reactions such as the oxidation of CO and organic substrates are reviewed. Finally the interface between nanotechnology and mass spectrometry is also considered.     

Catalytic Hydrodehydration of Cyclohexanone,Hydrogenation of 2-Cyclohexen-1-one,and Dehydrogenation of Cyclohexene over a Mo Chloride Cluster with an Octahedral Metal Framework

A silica gel-supported molybdenum halide cluster, (H₃O)₂[(Mo₆Cl₈)Cl₆]·6H₂O (1), developed selective catalytic activity for the condensation of cyclohexanone to cyclohexylbenzene and cyclohex-1-enylbenzene, when it was allowed to react in a stream of helium at 300°C. Halide clusters of Nb, Ta, and W of the same metal framework supported on SiO₂ also catalyzed the condensation at 400°C. However, at 400°C, 1 catalyzed disproportionation, and selectivity increased with increasing temperature, yielding cyclohexene and its dehydrogenation products, 1,3-cyclohexadiene and benzene, and 2-cyclohexen-1-one and its dehydrogenation product, phenol. When the same reaction was performed in a stream of hydrogen above 400°C, hydrodehydration proceeded almost exclusively, producing cyclohexene and its dehydrogenation products. 2-Cyclohexen-1-one was hydrogenated to cyclohexanone under the same reaction conditions utilizing hydrogen molecules, whereas cyclohexene was dehydrogenated via 1,3-cyclohexadiene to benzene. The active site developed on 1 was assumed to be a molybdenum atom, which becomes isoelectronic with the platinum metals by accepting two or more electrons from the ligands.     

稀土金属在不对称催化中的应用:从均相催化到异相催化

稀土金属的配位数较高,可通过容纳大型手性配体,构筑手性环境,催化不对称反应的定向发生,在工业生产特别是制药工程中具有重要应用价值.本文以Henry反应、Mannich反应和Strecker反应为例,总结回顾了稀土金属催化剂在此类反应中的设计思路、性能特点与应用前景,旨在展现稀土金属催化剂兼具融合均相催化与异相催化的优势...     

Triangular Clusters of Molybdenum Coordinated with Diethylthiocarbamate: Synthesis,Structure and Solution Behavior

Two novel clusters [Mo₃S₄(dtc)₃(μ-dtc)(L)] (where L = (CD₃)₂SO and tetrahydrothiophene, tht) were prepared and structurally characterized. The tht complex and its previously reported congener with L = py were studied by means of temperature-dependent ¹H NMR spectroscopy, indicating order of lability tht ? py.     

Bulky Phosphinines: From a Molecular Design to an Application in Homogeneous Catalysis

The design and preparation of an asymmetrically substituted and bulky phosphinine was achieved by introducing sterically demanding substituents into specific positions of a rigid phosphorus‐heterocyclic framework. Compound 5 shows, at the same time, axial chirality and a sufficiently high energy barrier for internal rotation to prevent enantiomerization. Both enantiomers of 5 were isolated by means of chiral analytical HPLC, and their absolute configurations could be assigned by combining experimental data and DFT calculations. Despite its substitution pattern, 5 can still coordinate to transition‐metal centers through the lone pair of electrons on the phosphorus atom. Rapid C? H activation on the adjacent aryl substituent at the 2‐position of the phosphorus heterocycle was achieved by using [{Cp*IrCl₂}₂] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) as a metal precursor. A racemic mixture of 5 was applied as a π‐accepting low‐coordinate phosphorus ligand in the Rh‐catalyzed hydroformylation of trans‐2‐octene, which showed a clear preference for the formation of 2‐methyloctanal.     

Alkoxide Clusters of Molybdenum and Tungsten as Templates for Organometallic Chemistry: Comparison with Carbonyl Clusters of the Later Transition Elements

Alkoxide and carbonyl ligands complement each other because they both behave as “π buffers” to transition metals. Alkoxides, which are π donors, stabilize early transition metals in high oxidation states by donating electrons into vacant d_π orbitals, whereas carbonyls, which are π acceptors, stabilize later transition elements in their lower oxidation states by accepting electrons from filled d_π orbitals. Both ligands readily form bridges that span M? M bonds. In solution fluxional processes that involve bridge–terminal ligand exchange are common to both alkoxide and carbonyl ligands. The fragments [W(OR)₃], [CpW(CO)₂], [Co(CO)₃], and CH are related by the isolobal analogy. Thus the compounds [(RO)₃W ? W(OR)₃], [Cp(CO)₂W?W(CO)₂Cp], hypothetical [(CO)₃Co?Co(CO)₃], and HC?CH are isolobal. Alkoxide and carbonyl cluster compounds often exhibit striking similarities with respect to substrate binding—e.g., [W₃(μ₃-CR)(OR′)₉] versus [Co₃(μ₃-CR)(CO)₉] and [W₄(C)(NMe)(OiPr)₁₂] versus [Fe₄(C)(CO)₁₃]—but differ with respect to M? M bonding. The carbonyl clusters use e_g-type orbitals for M? M bonding whereas the alkoxide clusters employ t_2g-type orbitals. Another point of difference involves electronic saturation. In general, each metal atom in a metal carbonyl cluster has an 18-electron count; thus, activation of the cluster often requires thermal or photochemical CO expulsion or M? M bond homolysis. Alkoxide clusters, on the other hand, behave as electronically unsaturated species because the π electrons are ligand-centered and the LUMO metal-centered. Also, access to the metal centers may be sterically controlled in metal alkoxide clusters by choice of alkoxide groups whereas ancillary ligands such as tertiary phosphanes or cyclopentadienes must be introduced if steric factors are to be modified in carbonyl clusters. A comparison of the reactivity of alkynes and ethylene with dinuclear alkoxide and carbonyl compounds is presented. For the carbonyl compounds CO ligand loss is a prerequisite for substrate uptake and subsequent activation. For [M₂(OR)₆] compounds (M = Mo and W) the nature of substrate uptake and activation is dependent upon the choice of M and R, leading to a more diverse chemistry.     

Hydrothermal Combination of Trilacunary Dawson Phosphotungstates and Hexanickel Clusters: From an Isolated Cluster to a 3D Framework

Three novel hexa‐Ni‐substituted Dawson phosphortungstates [Ni₆(en)₃(H₂O)₆(μ₃‐OH)₃(H₃P₂W₁₅O₅₆)] ? 14 H₂O ( 1 ), [Ni(enMe)₂(H₂O)][Ni₆(enMe)₃(μ₃‐OH)₃(H₂O)₆(HP₂W₁₅O₅₆)] ? 10 H₂O ( 2 ), and [Ni(enMe)₂]₃[Ni(enMe)₂(H₂O)][Ni(enMe)(H₂O)₂][Ni₆(enMe)₃(μ₃‐OH)₃(Ac)₂(H₂O)(P₂W₁₅O₅₆)]₂ ? 6 H₂O ( 3 ) (en=ethylenediamine, enMe=1, 2‐diaminopropane, Ac=CH₃COO^?) have been made under hydrothermal conditions and were characterized by IR spectroscopy, elemental analysis, diffuse reflectance spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. The common structural features of compounds 1 – 3 contain the similar hexa‐Ni‐substituted Dawson polyoxometalate (POM) units that can be viewed as a [Ni₆(μ₃‐OH)₃]⁹⁺ cluster capping on a [P₂W₁₅O₅₆]^12? fragment. Compounds 1 and 2 are two isolated clusters, whereas compound 3 is the first 3D POM framework constructed from hexa‐Ni‐substituted Dawson POM units and Ni(enMe) complex bridges. The preparations of compounds 1 – 3 not only indicate that triangle coplanar Ni₆ clusters are very stable fragments in both trivacant Keggin and trivacant Dawson POM systems, but also offer that the hydrothermal technique can act as an effective strategy for making novel Dawson‐type high‐nuclear transition‐metal cluster substituted POMs by combination of lacunary Dawson precusors with transition‐metal cations in the tunable role of organic ligands. In addition, magnetic measurements illustrate that there exist overall ferromagnetic interactions in compound 3 .     

Asymmetric Synthesis of Bicyclic Diol Derivatives through Metal and Enzyme Catalysis: Application to the Formal Synthesis of Sertraline

Enzyme‐ and ruthenium‐catalyzed dynamic kinetic asymmetric transformation (DYKAT) of bicyclic diols to their diacetates was highly enantio‐ and diastereoselective to give the corresponding diacetates in high yield with high enantioselectivity (99.9 % ee). The enantiomerically pure diols are accessible by simple hydrolysis (NaOH, MeOH), but an alternative enzyme‐catalyzed ester cleavage was also used to give the trans‐diol (R,R)‐ 1 b in extremely high diastereomeric purity (trans/cis=99.9:0.1, >99.9 % ee). It was demonstrated that the diols can be selectively oxidized to the ketoalcohols in a ruthenium‐catalyzed Oppenauer‐type reaction. A formal enantioselective synthesis of sertraline from a simple racemic cis/trans diol 1 b was demonstrated.     

Ring-Opening Polymerization of Lactones Initiated with Metal Hydroxide-Activated Macrocyclic Ligands: Determination of Mechanism and Structure of Polymers

Anhydrous alkali metal hydroxide (KOH, NaOH, and LiOH)-activated macrocyclic ligand complexing metal cations, i.e., coronands 12C4, 15C5, 18C6, DCH24C8, and cryptand C222, were selected for initiation of β-butyrolactone (β-BL) and ε-caprolactone (ε-CL) polymerization. It was found that β-BL polymerizes in the presence of KOH/18C6, KOH/C222, and NaOH/C222 systems. The real initiators in this case are two salts, potassium 3-hydroxybutyrate and potassium trans-crotonate, which are responsible for the formation of two fractions of the obtained polymer. ε-CL underwent polymerization with KOH or NaOH activated by all ligands used or without the ligand but with LiOH/12C4. Using KOH-activated strong ligands, i.e., 15C5, 18C6, or C222, two polymer fractions were generated containing linear and, unexpectedly, also cyclic macromolecules. The mechanism of the studied processes is discussed.     

综合化学实验：磁性金属有机骨架材料的合成及对铅的吸附

设计了一个综合实验——磁性金属有机骨架材料的合成及对铅的吸附。先合成四氧化三铁,再通过氨基修饰制备磁性金属有机骨架吸附材料。考察了此材料对铅的吸附性能,铅的浓度用火焰原子吸收光谱法测定。通过实验加深了学生对物理化学课程中吸附动力学等相关内容的理解,同时巩固了学生对仪器分析课程中的原子吸收光谱法的相关内容的掌握。     

含有Zn4O4簇的开放骨架结构磷酸锌的水热合成与表征

在水热体系中,以1,4-丁二胺为模板剂制备了Zn5(PO4)4·H3N(CH2)4NH3单晶,单晶结构分析表明,该化合物属正交晶系,Pnma空间群,晶胞参数a=1.83440(6)nm,b=1.33034(4)nm,c=0.74497(2)nm,β=90°,V=1.81801(9)nm3,Z=4,Dc=2.912Mg·m-3,最终因子R1=0.0309,wR2=0.0804[I>2σ(I)].结构中的锌和磷均与氧形成四面体配位,该化合物中含有Zn4O4簇,Zn4O4簇与PO4四面体相连,形成了篮子状亚结构基元,该亚结构基元通过氧桥以正反交替的方式相互连接成三维开放骨架结构.