One-dimensional polyoxometalate polymer constructed from V–W cluster by using asymmetrical bipyridine ligand

The asymmetrical organic molecule 2,4′-bipyridine (bpy) is explored to assemble polyoxometalate into a one-dimensional hybrid and compound [Cu^I(bpy)₂]₃[Cu^I₃(bpy)₄][V^VW^VI₉W^V₃O₄₀] (1) is achieved. Compound 1 represents a V-centered Keggin [V^VW^VI₉W^V₃O₄₀]⁶⁻ cluster bonded together by incorporating secondary metal coordination group of Cu–bpy. The thermogravimetric analysis of 1 has also been researched.     

Evaluation of a method for controlling molecular scaffold diversity in de novo ligand design

We describe an algorithm for the automated generation of molecular structures subject to geometric and connectivity constraints. The method relies on simulated annealing and simplex optimization of a penalty function that contains a variety of conditions and can be useful in structure-based drug design projects. The procedure controls the diversity and complexity of the generated molecules. Structure selection filters are an integral part and drive the algorithm. Several procedures have been developed to achieve reliable control. A number of template sets can be defined and combined to control the range of molecules which are searched. Ring systems are predefined. Normally, the ring-system complexity is one of the most elusive and difficult factors to control when fusion-, bridge- and spiro-structures are built by joining templates. Here this is not an issue; the decision about which systems are acceptable, and which are not, is made before the run is initiated. Queries for inclusion and exclusion spheres are incorporated into the objective function, and, by using a flexible notation, the structure generation can be directed and more focused. Simulated annealing is a reliable optimizer and converges asymptotically to the global minimum. The objective functions used here are degenerate, so it is likely that each run will produce a different set of good solutions.     

Bimetallic cluster complexes: synthesis, structures and applications to catalysis

A brief history of the seminal discoveries in the field of bimetallic cluster complexes with their structures is presented. A review of some recent studies of palladium and platinum-ruthenium cluster complexes is concluded with a discussion of applications of these complexes in the area of homogeneous hydrogenation catalysis of alkynes.     

Hybrid polyoxometalate palladacycles: DFT study and application to the Heck reaction

The phosphovanadotungstate polyanion [P₂W₁₅V₃O₆₂]^9? is a powerful support to stabilize palladacycles conjugated to the inorganic framework via an organic ligand. The insertion can be directed toward sp² or sp³ C–H insertion upon appropriate choice of the substitution pattern on the organic ligand. DFT modeling indicates that the strong withdrawing effect of the POM transmitted through the conjugated carbonyl was responsible for this easy insertion. The palladacycles led to the formation of stilbene via a Mizoroki–Heck reaction. However it is likely that the POMs act as Pd-reservoirs for the formation of nanoparticles.     

Supramolecular cluster catalysis: facts and problems

By checking the chemistry underlying the concept of “supramolecular cluster catalysis” we identified two major errors in our publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the “closed” cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺ (1) into the “open” cluster cation [H₂Ru₃(C₆H₆)(C₆Me₆)₂(O)(OH)]⁺ (2), which we had ascribed to a reaction with water in the presence of ethylbenzene is simply an oxidation reaction which occurs in the presence of air. (2) The higher catalytic activity observed with ethylbenzene, which we had erroneously attributed to the “open” cluster cation [H₂Ru₃(C₆H₆)(C₆Me₆)₂(O)(OH)]⁺ (2), was due to the formation of RuO₂ · nH₂O, caused by a hydroperoxide contamination present in ethylbenzene.     

Analysis of thin films and molecular orientation using cluster SIMS

A study of phenylalanine films of different thicknesses from submonolayer to 55 nm on Si wafers has been made using Bi_n⁺ and C₆₀⁺ cluster primary ions in static SIMS. This shows that the effect of film thickness on ion yield is very similar for all primary ions, with an enhanced molecular yield at approximately 1 monolayer attributed to substrate backscattering. The static SIMS ion yields of phenylalanine at different thicknesses are, in principle, the equivalent of a static SIMS depth profile, without the complication of ion beam damage and roughness resulting from sputtering to the relevant thickness. Analyzing thin films of phenylalanine of different thicknesses allows an interpretation of molecular bonding to, and orientation on, the silicon substrate that is confirmed by XPS. The large crater size for cluster ions has interesting effects on the secondary ion intensities of both the overlayer and the substrate for monolayer and submonolayer quantities. This study expands the capability of SIMS for identification of the chemical structure of molecules at surfaces. © Crown copyright 2010.     

The use of a versatile o-vanilloyl hydrazone ligand to prepare SMM-like Dy(3) molecular cluster pair

A novel lanthanide molecular cluster pair (MCP), displaying single molecule magnet behaviour, was assembled using the novel o-vanilloyl hydrazone ligand, versatile in terms of denticity, tautomerism and the rotatable C-C bond.     

Oxidation of alcohols using a manganese (II) complex based on a pentakis benzimidazole amide ligand

A pentakis benzimidazole based penta-amide ligand diethylenetriamine—N,N,N′,N′,N″-pentakis(2-methyl benzimidazolyl)penta-amide [GBDTPA] has been synthesized and utilized to prepare Mn (II) complexes of general composition [Mn₂(GBDTPA)X₄], where X is an exogenous anionic ligand (X = Cl⁻, NO₃⁻ and Br⁻). The oxidation of alcohols has been investigated using [Mn₂(GBDTPA)Cl₄] as the catalyst and TBHP as an alternate source of oxygen. The respective aldehydic products have been isolated and characterized by ¹H NMR.     

Highly selective and efficient oxidation of sulfides with hydrogen peroxide catalyzed by a chromium substituted Keggin type polyoxometalate

The catalytic oxidation of sulfides into the corresponding sulfones by a chromium substituted Keggin type polyoxometalate, (TBA)₄[PW₁₁CrO₃₉]·3H₂O, was achieved using mild reaction conditions. Excellent yields were obtained using four equivalents of 30% H₂O₂. Under these reaction conditions, the sulfide group was highly reactive and other functional groups such as hydroxyl or a double bond were unaffected. Using a commercially available, eco-friendly, and cheap oxidant, mild reaction conditions, operational simplicity, practicality, short reaction times, high to excellent yields, and excellent chemoselectivity are some of the advantages of this catalytic system.     

Organonickel chemistry in the catalytic hydrodechlorination of polychlorobiphenyls (PCBs): ligand steric effects and molecular structure of reaction intermediates

Soluble homogeneous organophosphorus—nickel complexes have been used to detoxify polychlorinated biphenyls (PCBs) by catalyzed hydrodechlorination using NaBH₂(OCH₂CH₂OCH₃)₂ as the hydrogen source. The reactions appear to proceed by NiL₃ oxidative addition into C---Cl bonds followed by hydrogenolysis of the metal---carbon bond. In model experiments with decachlorobiphenyl, the cone angle of the organophosphorus ligand L was shown to be a key factor controlling the magnitude and position of chlorine displacement. Hence, ligands leading to para displacement (e.g. (o-MeC₆H₄O)₃P), meta—para displacement (e.g. (EtO)₃P and (PhO)₃P), and ortho—meta—para displacement (e.g. Me₃P and Et₃P) were found. Significantly, the highly toxic, coplanar dioxin precursor 3,3′,4,4′-tetrachlorobiphenyl, a meta—para chlorine-substituted congener, was dechlorinated quantitatively with the Et₃P catalyst system. Evidence for the presence of organonickel intermediates in the reaction mixtures was obtained by mass spectroscopic and X-ray diffraction studies. Of particular interest is the isolation of square planar complexes p-C₆Cl₅C₆Cl₄Ni(PEt₃)₂Cl from the reaction of decachlorobiphenyl with NaBH₂(OCH₂CH₂OCH₃)₂—(Et₃P)₂NiCl₂ as the catalyst precursor and m-C₆Cl₅C₆Cl₄Ni(PEt₃)₂Cl from decachlorobiphenyl—Ni(1,5-C₈H₁₂)₂—PEt₃ at room temperature. All are oxidative addition intermediates and precursors for decachlorobiphenyl hydrodechlorination.     

Synthesis of covalently bonded nanostructure from two porphyrin molecular wires leading to a molecular tube

Molecular wire, diacetylene-linked porphyrin dimer 6 having terminal alkenes, was synthesized. Porphyrin dimer 6 formed the 1:1 double-stranded ladder complex with 1,4-diazabicyclo[2.2.2]octane (DABCO). The co-planar stacked two porphyrin molecular wires in the ladder complex were connected by olefin metathesis in the presence of the Grubbs catalyst in order to make a covalently bonded tubular nanostructure. The obtained molecular tube 7 was characterized by ¹H, ¹³C NMR spectroscopy, and MALDI-TOF MS spectrometry.     

Metal-selective coordination and enhanced fluorescence of a self-assembling ligand scaffold

A fluorescent hydroxyiminonicotinonitile (HINT) coordinating group can be incorporated into self-assembling ligand scaffolds, and shows metal-selective assembly and enhanced fluorescence. The assembly process is dependent on ligand coordination angle, and coordination only occurs for oxophilic first row transition metal ions, with affinity enhanced by the supramolecular assembly process. The ligands are weakly emissive, and show strong enhancement in fluorescence upon Zn²⁺ coordination, whereas Co²⁺ or Fe²⁺ cause complete quenching.     

Mild and efficient copper-catalyzed N-arylation of alkylamines and N-H heterocycles using an oxime-phosphine oxide ligand

A mild and efficient copper-catalyzed system for N-arylation of alkylamines and N-H heterocycles with aryl iodides using a novel, readily prepared and highly stable oxime-functionalized phosphine oxide ligand was developed. The coupling reactions could even be performed in solvent-free conditions with moderate to good yields.     

Palladium(II)-catalyzed arylation of unactivated C(sp3)-H bonds by using 2,1,3-benzoselenadiazole-4-amine as directing ligand

A modified bidentate directing ligand derived from 2,1,3-benzoselenadiazole (BSeD) was designed and synthesized. It exhibited high regioselectivity in the catalytic activation of unactivated C(sp³)-H bonds with aryl iodides in the presence of palladium catalyst in yields up to 94%.     

Identifying ligand binding sites and poses using GPU-accelerated Hamiltonian replica exchange molecular dynamics

We present a method to identify small molecule ligand binding sites and poses within a given protein crystal structure using GPU-accelerated Hamiltonian replica exchange molecular dynamics simulations. The Hamiltonians used vary from the physical end state of protein interacting with the ligand to an unphysical end state where the ligand does not interact with the protein. As replicas explore the space of Hamiltonians interpolating between these states, the ligand can rapidly escape local minima and explore potential binding sites. Geometric restraints keep the ligands from leaving the vicinity of the protein and an alchemical pathway designed to increase phase space overlap between intermediates ensures good mixing. Because of the rigorous statistical mechanical nature of the Hamiltonian exchange framework, we can also extract binding free energy estimates for all putative binding sites. We present results of this methodology applied to the T4 lysozyme L99A model system for three known ligands and one non-binder as a control, using an implicit solvent. We find that our methodology identifies known crystallographic binding sites consistently and accurately for the small number of ligands considered here and gives free energies consistent with experiment. We are also able to analyze the contribution of individual binding sites to the overall binding affinity. Our methodology points to near term potential applications in early-stage structure-guided drug discovery.     

基于Keggin型金属氧簇与含氮有机配体自组装超分子化合物的晶体结构和电化学研究

通过水热方法合成了超分子化合物(H2bbi)2(SiW12O40).H2O.单晶X射线衍射分析表明化合物结晶于三斜晶系,P-1空间群.化合物中的两种亚单元通过氢键作用形成了超分子结构.此外,循环伏安法研究结果表明了化合物展示3个连续的双电子还原过程.     

Synthesis and molecular structures of lanthanocene amide complexes and their catalytic activity for addition of amines to nitriles

Reaction of (CH₃C₅H₄)₂LnCl(THF) with NaNHAr in a 1:1 molar ratio in THF afforded the amide complexes (CH₃C₅H₄)₂LnNHAr(THF) [(Ar = 2,6-Me₂C₆H_3, Ln = Yb (I), Y (III); Ar = 2,6-ⁱPr₂C₆H₃, Ln = Yb (II)]. X-ray crystal structure determination revealed that complexes I-III are isostructural. The central metal in each complex coordinated to two methylcyclopentadienyl groups, one amide group and one oxygen atom from THF to form a distorted tetrahedron. Complexes I-III and a known complex (CH₃C₅H₄)₂YbNⁱPr₂(THF) IV all can serve as the catalysts for addition of amines to nitriles to monosubstituted N-arylamidines. The activity depended on the central metals and amide groups, and the active sequence follows the trend IV ≈ III < I < II.