Browsing by Subject "Lewis acid"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Heavy atom induced phosphorescence of organic materials using mono- and trifunctional organomercury derivatives(2009-05-15) Burress, Charlotte NicoleThis dissertation focuses on the phosphorescence of organic chromophores using perfluoro-ortho-phenylene mercury (1) and bis(pentafluorophenyl)mercury (2) as external heavy atom effect inducers. To ascertain the suitability of these luminescent adducts for OLED applications, several research objectives have been investigated. To further shorten the triplet lifetimes of adducts involving 1, a strategy was developed which combines both internal and external heavy atom effects. Specifically, complexes involving 1 and N-methylcarbazole, N-methylindole and the 1- halonaphthalenes were investigated. The existence and stability of the complexes could be confirmed in solution by fluorescence spectroscopy. In the solid state, these adducts form supramolecular binary stacks where the molecules of 1 alternate with the aromatic substrate. As a result of the mercury external heavy atom effect, all of these adducts display intense room temperature phosphorescence of the free arene. With the Nheterocycles, the triplet lifetimes were drastically reduced to below 100 mu-s. To appreciate the origin of the unusual heavy atom effects observed in arene adducts with 1, 2 was studied as a monofunctional analog to 1. By utilizing fluorescence spectroscopy, naphthalene, biphenyl, and fluorene complexes of 1 and 2 have been detected in solution. The solid state structure of the adducts with 2 reveal supramolecular binary stacks. Comparison of the photophysical results supports the occurrence of cooperative effects between the Lewis acidic mercury centers of 1, which make it a more efficient external heavy-atom effect inducer. Polymeric materials which are amenable to deposition in thin layers were investigated as substrates for 1 and 2. Both poly(vinyl-2-naphthalene) and poly(vinylcarbazole) interact with 1 and 2 in solution as evidenced by fluorescence spectroscopy. With the solid blend 1?PVK, a small doping percentage of 1 results in white emission, while larger percentages of 1 yield bright orange emission. This dissertation presents the first structurally characterized ternary complex with 1, carbazole, and coordinating solvents THF and triethylamine. IR spectroscopy and short N???O and N???N distances in the solid state indicates that the acidic N-H moiety of carbazole interacts with the solvent by hydrogen bonding. In the extended structure, molecules of 1 and the hydrogen bonded complex alternate to form supramolecules.Item Synthesis and Study of Boron and Antimony Lewis Acids as Small Anion Receptors and Ligands Towards Transition Metals(2012-02-14) Wade, CaseyAlthough fluoride is used at low concentrations in drinking water as a means of promoting dental health, it poses a danger at high exposure levels where it can lead to skeletal fluorosis or other adverse effects. Cyanide is notoriously toxic, and its large scale use in industrial processes warrants the need for close monitoring to remain aware of potential contamination of water sources and other environmental resources. Based on these considerations, it is critical to continue to develop improved methods of monitoring fluoride and cyanide concentrations in water. However, molecular recognition of these anions in water poses considerable challenges. For fluoride, this is due largely to its high hydration enthalpy (?Ho = -504 kJ mol-1), which drastically reduces its reactivity in water. Additionally, the strong basicity of cyanide (pKa of (HCN) = 9.3) may obscure its detection in neutral water due to protonation. In addition to achieving detection of these anions in water, it is most desirable to have information of the detection event relayed in the form of a positive, rather than negative, response (i.e., turn-on vs turn-off). The general strategy of appending cationic groups to triarylboranes imparts beneficial Coulombic, inductive, and sometimes chelate effects that have allowed a number of these Lewis acidic receptors to sense fluoride and cyanide in aqueous environments. With the goal of developing new triarylborane-based receptors that show enhanced affinities for these anions, as well as turn-on responses to detection, a series of pyridinium boranes were synthesized and studied. Having recognized that the inherent Lewis acidity of antimony(V) species might be exploited for anion sensing, we also describe initial studies on the ability of tetraorganostibonium ions (R4Sb+) and cationic transition metal-triarylstibine complexes (R3SbM+) to complex fluoride. Finally, the electropositivity of antimony and its ability to form stable compounds in both the +3 and +5 oxidation states have led us to begin investigations into the bonding and redox reactivity of novel metal stibine/stiborane complexes.Item Synthesis, Characterization and Anion Binding Properties of Boron-based Lewis Acids(2012-07-16) Zhao, Hai YanThe recognition and capture of fluoride, cyanide and azide anions is attracting great deal of attention due to the negative effects of these anions on the environment and on human health. One of common methods used for the recognition and capture of these anions is based on triarylboranes, the Lewis acidity of which can be enhanced via variation the steric and electronic properties of the boron substituents. This dissertation is dedicated to the synthesis of novel boron-based anion receptors that, for the most part, feature an onium group bound to one of the aryl substituents. The presence of this group is shown to increase the anion affinity of the boron center via Coulombic effects. Another interesting effect is observed when the onium group is juxtaposed with the boron atom. This is for example the case of naphthalene-based compounds bearing a dimesitylboryl moiety at one of the peri-position and a sulfonium or telluronium unit at the other peri position. Fluoride anion complexation studies with these sulfonium or telluronium boranes, show that the boron-bound fluoride anion is further stabilized by formation of a B-F->Te/S bridge involving a lp(F)->sigma*(Te/S-C) donor acceptor interaction. Some of the sulfonium boranes investigated have been shown to efficiently capture fluoride anions from wet methanolic solutions. The resulting fluoride/sulfonium borane adducts can be triggered to release a "naked" fluoride equivalent in organic solution and thus show promise as new reagents for nucleophilic fluorination chemistry. Interestingly, the telluronium systems show a greater fluoride anion affinity than their sulfonium analogs. This increase is assigned to the greater spatial and energetic accessibility of the sigma* orbital on the tellurium atom which favors the formation of a strong B-F->Te interaction. This dissertation is concluded by an investigation of the Lewis acidic properties of B(C6Cl5)3. This borane, which has been reported to be non-Lewis acidic by other researchers, is found by us to bind fluoride, azide and cyanide anions in dichloromethane with large binding constants. This borane is also reactive toward neutral Lewis bases, such as p-dimethylaminopyridine, in organic solvents.Item Synthesis, Characterization and Reactivity of Electrophilic Organometallic Compounds of Ruthenium, Tantalum and Silicon(2014-12-11) Ramirez, RodrigoThe work presented herein will discuss the synthesis, characterization and reactivity of electrophilic organometallic compounds of ruthenium, tantalum, and silicon in order to explore unusual properties, reactivity, or structure. Several of the chemical species described are cationic, electronically and coordinatively unsaturated, and require the use of weakly coordinating anions in order to retain their high electrophilic character. The first study consisted in the devolpment of a method to synthesize C?alkylated carborane anions of the type [RCB11Cl11]^? (R = Me, Et, Pr, Bu, Hex) was developed, in order increase the solubility of its salts in weakly coordinating organic solvents. Salts of these C?alkylated anions form crystalline compounds. On the basis of this work, the possibility of the synthesis of a silylium?like zwitterionic compound was investigated. The compound was designed around the anionic [CB11Cl11]^? fragment, attached covalently via the C?vertex to a silylium?type cation through a methylene linker. Its synthesis was succesfuly achieved, and an X?ray diffraction study of this compound revealed that the cationic silicon center is stabilized intramolecularly by weak coordination to a chlorine atom on the ortho B?Cl ring of the anionic fragment. This compound retains the fundamental structural and chemical features of its two?component counterparts, but it is extraordinarily insoluble in weakly coordinating organic solvents. This feature can be traced back to the inherent molecular symmetry and charge distribution. The synthesis of a family of d^6 ML5 and d^6 ML6 ruthenium triflate complexes of the pincer (P2C=)Ru(X) (X = Cl, H, OAc, acac) architecture by ligand exchange using Me3SiOTf will be presented. It was speculated that metathesis of chloride with the more weakly coordinating triflate would be a convenient way to generate compounds that could be potential Lewis?acidic precatalysts. These compounds can be regarded as synthetic equivalents of truly cationic complexes, with the added advantage that no need for the isolation of highly reactive species is necessary. Finally, the reactivity of (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl towards internal and terminal alkynes was investigated. In addition to this, chloride abstraction from (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl was effected, in order to potentially enhance any reactivity towards internal and terminal alkynes. It was found that, upon chloride abstraction from neutral (?^5?C5Me5)Ta(?CPh)(PMe3)2Cl, a reversible C?H bond activation process at PMe3 takes place, concomitant with protonation of the carbyne to form two cationic, isomeric alkylidenes of the type [(?^5?C5Me5)Ta(=CHPh)(CH2PMe2)(PMe3)]^+. In terms of reactivity towards alkynes, it was found that both the neutral and cationic systems form stable tantalacyclobutadienes, one of which was characterized structurally through an X?ray diffraction study.Item Trimeric perfluoro-ortho-phenylene mercury as a building block for supramolecular materials(Texas A&M University, 2006-04-12) Haneline, Mason ReamesTrimeric perfluoro-ortho-phenylene mercury (1) constitutes one of the simplest trifunctional Lewis acidic hosts. Cooperative effects arising from the proximity of the mercury(II) centers, the electron-withdrawing properties of the backbone and the accessibility of the electrophilic sites leads to the facile complexation of neutral and electron rich substrates. The planarity of the structure as well as its overall polarizability compounded with relativistic effects at mercury also permits the occurrence of non-covalent interactions. The main objective of this dissertation was to explore the potential of 1 as a building block for supramolecular materials. Compound 1 was investigated using single crystal x-ray diffraction and was found to display a rich polymorphism. The electronic structure, probed by DFT methods, shows that the LUMO of 1 has a large contribution from the mercury 6p orbitals and features a large lobe protruding above and below the center of the trinuclear mercury core. Complexes in which two nitronyl nitroxide radicals (NIT-Ph = 2-(phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) coordinate to the trinuclear core of 1 above and below the Hg3 plane reveal that 1 does not significantly mediate magnetic interactions. The ability of 1 to complex π-basic molecules such as tetrathiafulvalene (TTF), toluene, o-xylene, m-xylene, p-xylene, mesitylene, biphenyl, naphthalene, acenaphthalene, anthracene, pyrene, triphenylene, perylene, and coronene was also investigated and show that 1 and arenes form extended binary stacks in which the two components alternate. The photoluminescence observed in some of these supramolecular complexes corresponds to the phosphorescence of the arene indicating a mercury heavy atom effect. Complexation of 1 in solution was observed with hexaalkoxytriphenylenes (HATn, n = 1, 6) by fluorescence and NMR spectroscopy. Finally, compound 1 forms electrophilic double sandwich structures with ferrocene and nickelocene in which a molecule of 1 caps each of the Cp ligands. The nickelocene adduct is stabilized towards oxidation, and the photophysical and magnetic properties indicate the occurrence of a mercury heavy atom effect.