4,688 research outputs found

    Synthesis and characterization of transition metal cluster containing diphosphine ligands

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    Various metal complexes containing transitional metal elements have been prepared. Using shlenk line technique . Spectroscopic analysis by IR and NMR shows that two types of diphosphine co-ordinated metal clusters have been obtained,one having chelating mode of binding [Fe3SeTeCO)7{(PPh2)(C5H4)Fe(C5H4)(PPh2)}] ,and the another is having mono dentate co-ordination [Fe3Te2(CO)8{(PPh2) (C5H4)Fe(C5H4)(PPh2)}]

    Doctor of Philosophy

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    dissertationLinear free energy relationships have been a staple of reaction mechanistic studies for nearly 100 years, enabling the quantification of subtle steric and electronic interactions between ligand, catalyst, and substrate. Recent work has offered an integrated approach to both interrogate reaction selectivity origins and to predict more optimal conditions. Classic and modern approaches to analyze ligand effects are presented in Chapter 1. Chapter 2 focuses on the development of novel descriptors for monodentate phosphine ligands. The application of these parameters to a Suzuki reaction was complicated by multiple ligation states of the catalyst. Experimental outcomes indicated that two catalyst regimes are present in the reaction; thus, separation of the results into subclasses was necessary. Doing so simplified the selectivity models, revealing nuanced ligand effects that were quantified with the new parameters. Further applications of these phosphine descriptors are detailed in Chapter 3. First, two gold-phosphine catalyzed cycloisomerization reactions are investigated using physical organic techniques along with reaction selectivity correlations. Overall, these data are used to identify the origin of ligand induced chemoselectivity, and to predict a novel ligand to increase the desired product ratio. Second, studies of an alkyl-aryl Suzuki reaction are described. In this instance, the phosphine ligand is shown to affect the enantiospecificity and chemoselectivity in two different fundamental steps. Evidence of the role ligand size and electronics play in directing the reaction pathways are presented. Chapter 4 details our team's efforts to identify a catalyst system that favors the atypical oxidative addition pathway within a Buchwald-Hartwig coupling reaction of differentially halogenated hetero-aromatics. Bidentate phosphine ligands were found to induce moderate selectivity; thus, ligand parameterization was utilized. Guided by univariate correlations, an exceedingly selective diaminophosphine ligand was successfully predicted, the origins of which were additionally analyzed with density functional theory (DFT) calculations. Using similar multivariate techniques, Chapter 5 presents the parameterization of acyclic diaminocarbene ligands developed in the context of a gold-catalyzed rearrangement-cyclization reaction. Enantioselectivity in this case was found to be highly sensitive to two substituents on the ligand, and quantification of these effects enabled the identification of a reaction system that produces highly enantioenriched products

    Designing organometallic compounds for catalysis and therapy

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    Bioorganometallic chemistry is a rapidly developing area of research. In recent years organometallic compounds have provided a rich platform for the design of effective catalysts, e.g. for olefin metathesis and transfer hydrogenation. Electronic and steric effects are used to control both the thermodynamics and kinetics of ligand substitution and redox reactions of metal ions, especially Ru II. Can similar features be incorporated into the design of targeted organometallic drugs? Such complexes offer potential for novel mechanisms of drug action through incorporation of outer-sphere recognition of targets and controlled activation features based on ligand substitution as well as metal- and ligand-based redox processes. We focus here on η 6-arene, η 5-cyclopentadienyl sandwich and half-sandwich complexes of Fe II, Ru II, Os II and Ir III with promising activity towards cancer, malaria, and other conditions. © 2012 The Royal Society of Chemistry

    A new charge-transfer complex in UHV co-deposited tetramethoxypyrene and tetracyanoquinodimethane

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    UHV-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), X-ray-diffraction (XRD), infrared (IR) spectroscopy and scanning tunnelling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d1= 0.894 nm, d2= 0.677 nm). A softening of the CN stretching vibration (red-shift by 7 cm-1) of TCNQ is visible in the IR spectra, being indicative of a CT of the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts of the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of from DFT calculations (Gaussian03 with hybrid functional B3LYP). STS reveals a HOMO-LUMO gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0 eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods.Comment: 20 pages, 6 figure

    Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium : biological relevance and synthetic strategies

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    This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B–H activation, transmetalation reactions and/or direct formation of metal–metal bonds are discussed (103 references)

    Cationic Ruthenium Complexes in Catalysis: The Activation of Propargylic Alcohols Through Electronically Tuned Complexes

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    With increasing complexity of metal complexes, it is of worthwhile interest to pursue systematic examinations of ligand modifications to study their impact on the reactivity of a catalyst. To that end, this study aimed to understand the effect electron-withdrawing ligands conveyed to catalytic activity in the etherification of propargylic alcohols and related reactions. A number of half-sandwich ruthenium complexes bearing ligands with varying electron–withdrawing properties were synthesized and structurally characterized. Their electronic and structural properties were investigated utilizing X-ray crystallography, revealing that the series of complexes did not vary significantly in structure. The complexes were studied electronically with cyclic voltammetry, which discovered that the coordinated electron-withdrawing ligands resulted in complexes that were more difficult to oxidize and with possibly decreased electron density at the ruthenium center. All complexes showed catalytic activity in the etherification of propargylic alcohols and in the formation of oxygen-containing heterocycles from propargylic alcohols and diketones. Thermal instability offers an explanation as to why some catalyst systems do not perform very well at elevated temperatures. In a separate study, a more stable tridentate ligand was employed as an architecture for further study in this electronic fine-tuning methodology. A new ruthenium complex bearing a tridendate diacetylpyridine ligand was synthesized, characterized, and employed as catalyst in the coupling of carboxylic acids to terminal alkynes to form enol esters with good regioselectivity. Iron offers a number of advantages in transition metal catalysis, as it is inexpensive and relatively non-toxic. Based on preliminary findings from the Bauer laboratory, an in situ catalyst formed through oxidation of ferrocene boronic acid was found to be catalytically active in the etherification of propargylic acetates. Most interestingly, and opposed to all catalytic reactions performed for this study, the ferrocenium cation does not require elevated temperatures and performs well at room temperature

    Electrosynthesis and characterisation of functionalised poly(indoles)

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