N-heterocyclic carbenes (NHCs) can be used as ligands for organometallics complexes, which can then facilitate numerous catalytic applications, such as, C-H activation, small molecule activation and numerous materials applications. The use of anionically-tethered NHCs for usage with electropositive metals has been pioneered by the Arnold group within the last decade. This thesis describes the synthesis of both aryloxide- and amide-tethered NHC organometallic complexes of s-, p-, d- and f-block metals to provide a platform for small molecule activation. Once synthesised, the reactivity of some of these complexes were tested by reaction with CO2 with the aim of turning a molecule considered a harmful (environmentally), waste product into value added products, potentially providing an alternative fuel source. Chapter One introduces the use of anionically-tethered NHCs for use in a number of organometallic complexes as well as their current potential as catalysts for a number of important small molecules. This chapter focuses upon the differences between complexes tethered with anionic O, N, P, S elements, f-element NHC complexes and the use of d-block NHC complexes for catalysis. Chapter Two contains the synthesis and characterisation of a number of aryloxy-tethered NHC p-, d- and f-block organometallic complexes using the ligand H2(LArO R)2. The synthesis of SnII complexes including the synthesis of new ‘normal’ ‘abnormal’ complexes given enough steric bulk around the Sn centre due to the lone pair present in Sn complexes, preventing one of the ligands binding through the classical carbene position and therefore binding through the backbone C4 carbon. The synthesis of MII (Zn, Co and Fe) complexes to compare the solid-state structure and binding mode of the carbenes. The synthesis and characterisation of MIII (Ce and Eu) complexes to assess the solid-state structure and binding modes within f-bock complexes. Chapter Three investigates the reactivity of the MII complexes (Sn, Zn, and Fe) with CO2. Successful reactions were characterised using NMR and further treated with alkynes to target catalytic reactions. Chapter Four contains reactions to target a number of amide-tethered bis (NHC) s-, p-, d- and f-block organometallic complexes using the proligand, H4(LN Mes)Cl3. Deprotonation studies undertaken with a number of bases to give the MI (Li and K) salts and MII (Mg) salts and proved to be unsuccessful upon isolation. Reactions to synthesise the p-, d- and f-block complexes were then undertaken using in situ free carbene production as well as the attempted isolation of the free carbene, both of which also proved unsuccessful. Chapter Five provides an overall conclusion to the work presented in Chapters Two, Three and Four within this thesis. Chapter Six gives the experimental and characterising data for the complexes and reactions.

This study aims synthesis of metal/polymer one dimensional nanostructures by micelle formation, reduction, and electrospinning route, and to analyze the morphological characteristics of composite nanofibers. The study was carried out in three main steps. First, the reverse micelle structures were established between the anionic surfactant and the metal ion. The surfactant acts as an agent to bind metal ions together so that the arrangements of metal ions can be controlled in the solution. As the surfactant concentration increases, reverse micelles grow and reverse wormlike micelle structures are observed. Wormlike micelles are elongated semi flexible aggregates which form a spherocylinder form repeating units. Metal ions are in the core and surrounded with the surfactant. The polymer attached to the wormlike structure acts as a shield and prevents phase separation in a hydrophilic medium. Different polymer and surfactant concentrations were tried to determine the optimum polymer and surfactant concentrations for reverse micelle formation. The size analyses of the reverse micelle structures were done by dynamic light scattering technique. In the second step, metal ions in the micelles were reduced by using hydrazine hydrate to obtain metal cores in the center of wormlike micelles. Finally, electrospinning was carried at room temperature and in air atmosphere. The characterization of nano composites was done by Scanning Electron Microscopy. It was found that the size of the reverse micelle structures affects the distribution of metal nano partices in polymer nano fibers. In order to distribute the metal nano particles homogeneously, the optimum size of reverse wormlike micelles was found to be between 420 and 450 nm.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Charles G. Riordan, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

This Thesis describes the syntheses, characterisation and reactivity of rare earth metal boryl and gallyl compounds. Experimental and computational studies were performed to investigate the structure and bonding in these compounds. <b>Chapter 1</b> introduces key metal-boryl and metal-gallyl compounds of the s, p, d and f-blocks via literature review. <b>Chapter 2</b> describes the syntheses, structures and bonding analyses of rare earth metal boryl compounds. A short introduction to rare earth metal cations is given. Chapter 3</b> describes the syntheses, structures and bonding analyses of rare earth metal gallyl compounds. The preparation of a new class of rare earth metal cations will also be reported. A short introduction to rare earth metal amidinates is given. <b>Chapter 4</b> presents reactivity studies of the rare earth metal gallyl compounds described in Chapter 3. To facilitate a direct structure and reactivity comparison, the corresponding boryl compounds were also synthesised. The results of a comprehensive DFT computational study to investigate the structure and bonding in these compounds are also presented. A short introduction to metalelement and metalmetal bond reactivity is given. <b>Chapter 5</b> presents full experimental procedures and characterising data for the new compounds reported. <b>Appendix<b> <b>CD Appendix</b> contains .cif files for all new crystallographically characterised compounds described.

This organometallic study involves the use organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are typically electrophilic and are stabilized by a single π-donor substituent, and contain low oxidation state metals (often but not always from Group 6). They are highly reactive and can give access to a range of biologically active compounds through cyclopropanations, insertions, coupling and photochemical reactions. Synthesis and characterization of three MOM-protected α-alkoxy organostannanes was successfully carried out via a nucleophilic addition of tributylstannyllithium to suitable aldehydes, and immediate protection of the alcohol with MOM. Two N-BOC protected α-amino organostannanes were successfully synthesized and characterized via α-lithiation and tin-lithium exchange in the presence of TMEDA. Tin-lithium transmetallation of the organostannanes allowed access to the organolithiums required for the synthesis of novel Fischer carbenes. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with Meerwein salt, resulting in the Fischer carbene and a by-product, tetrabutyltin, which proved difficult to remove. Several Fischer carbenes were synthesized and characterized, some simple and known and some novel. In silico work explored the reaction coordinate of the [2+2] cycloaddition towards the formation of β-lactams, and the photoactivation cycle that precedes this process. Computational work also showed the effect of the ligand on the stability and reactivity of the carbene. It was found that in some cases the oxygen on the ligand could negatively influence the stability of the carbene (when compared to a simple methyl carbene). A link between bond orders and back donation in Fischer carbenes was explored in an attempt to theoretically predict the stability of a range of carbenes. / Microsoft� Office Word 2007

This investigation deals with the preparations of cyclic organosilanes via two different types of organometallic precursors: borane adducts to chlorovinylsilanes and tertbutyllithium adducts to chlorovinylsilanes. The regiospecificity of the hydroboration of various types of boranes to chlorovinylsilanes was studied by three different methods. It was found that, by using bulky hydroborating agents, about 80% isomerically pure terminal borane adducts to chlorovinylsilanes could be obtained. While the adducts are potential precursors to silacyclopropanes, when these borane adducts were treated with bases such as sodium methoxide and methyl Grignard, no evidence for silacyclopropane formation was found.

<p>While crucial advancements have been made in understanding transition metal−nitrogen interactions, the actinides have not been studied in such depth as their transition metal counterparts. Uranium has shown to catalyze the Haber−Bosch process to produce NH₃ but more attention has turned to transition metals such as iron due to their low cost and accessibility. It is thought that transition metal imido species are essential intermediates to this process; therefore, it is critical to understand NH bond cleavage and formation on the metal. To study the potential that uranium has, it is important to bridge the knowledge gap of uranium with its transition metal counterparts and further understand NH bond cleavage and formation on the metal to make the suspected imido intermediate.</p> <p>Redox neutral methods have been popular and effective for synthesizing uranium imido complexes such as starting with a uranium(IV) amide and deprotonating it with a base to yield its respective uranium(IV) imido. It was of interest to understand if the bisTp* uranium(III) system would be amenable to a deprotonation pathway. To test this, the reactivity of Tp*₂UBn with bulky 4-(2,6-di(pyridin-2-yl)pyridin-4-yl)benzenamine (terpy-aniline) and sterically smaller p-toluidine (ptol-aniline) was explored to first synthesize uranium(III) anilido species. Following successful synthesis, their reactivity is explored to yield respective uranium(IV) imido species by oxidative deprotonation.</p> <p>In addition to redox neutral methods, synthetic processes that rely on redox reactions at the uranium center have also been successful but are less common since the starting material must be a stable, low-valent uranium species. Our group has explored this method to make uranium(IV) imido species where the addition of 1 equivalent of organic azide to trivalent Tp*₂UBn or one equivalent of organic azide and potassium graphite to Tp*₂UI results in the formation of uranium(IV) imido species. The downside to this is azides are explosive and their synthesis could inhibit synthesis of diverse complexes. A redox method that eliminated usage of explosive azides is of interest so the reactivity of hydrogen atom transfer (HAT) reagents, Gomberg’s dimer or the 2,4,6-tri-tBu-phenoxy radical (·OMes*), with uranium(III) anilido complexes of varying steric bulk and electronic profile was explored. Conversion to their respective uranium(IV) imido species was achieved and this method was also explored with uranium(III) amides smaller than a phenyl since their respective azide are too dangerous to synthesize.</p> <p>Following isolation of uranium(III) anilido complexes and exploring reactivity it was of interest to understand how they compare to phosphorus analogues and how reactivity and interactions might be similar. Reactivity of Tp*₂UBn with phosphines of various steric bulk and electronic profile allowed for the isolation of uranium(III) phosphido complexes and their reactivity showed to be different than previously explored uranium(III) anilido counterparts. The electronic differences of the pnictogens were also observed in the crystal structures.</p> <p>With the differences in reactivity and electronic effects between the nitrogen and phosphorous complexes having been observed, our curiosity expanded to explore more uranium-pnictogen interactions. Therefore, synthesis of bis-substituted arsine and bis-substituted phosphine ligands were conducted for reactivity with Tp*₂UBn. Preliminary data reveals these bonds are more unstable and reactive relative to uranium(III) anilido species, likely due to the electronic mismatch between oxophilic uranium and soft pnictogens. Where applicable, compounds were characterized by multinuclear NMR spectroscopy, infrared spectroscopy, electronic absorption spectroscopy, single crystal X-ray crystallography, and quantum chemical calculations.</p>

<p>  </p> <p>This thesis will focus on two broad topics: the synthesis and characterization of various diruthenium aryl compounds and of mono- and bis-alkynyl unsymmetric compounds based on Ru(II)(dppm)₂ and Ru(II)(dppe)₂ bridges (dppm = 1,2-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphophino)ethane).</p> <p>Chapters 1–3 focus on multiply bonded metal–metal compounds, utilizing four different ‘paddlewheel’ motifs (dinuclear ruthenium units that are supported by four bidentate ligands). These highly stable mono- and bis-aryl diruthenium compounds are readily prepared using lithium-halogen exchange reactions. Two different oxidation states have been accessed, Ru₂(II,III) and Ru₂(III,III), through modification of the paddlewheel ligands or coordination of a small, π-accepting ligand at the vacant ruthenium site in Ru₂(<em>ap</em>)₄(Ar) compounds (<em>ap</em> = 2-anilinopyridinate; Ar = aryl). Chapter 1 discusses the modification of the bidentate ligand to yield two unique Ru₂(<em>ap</em>')₄(Ar) series, which both exhibit improved solubility over the previously reported un-modified Ru₂(<em>ap</em>)₄(Ar) series, and the structural, electronic, and optical characterizations of the compounds within these two new Ru₂(II,III) series. Chapter 2 builds upon our lab’s previous studies on electron transfer between the two ruthenium centers in [Ru₂(<em>ap</em>)₄]₂(μ-C≡C)_x compounds and applies this towards synthesizing and characterizing mixed-valency within a Ru₂(III,III) phenylene bridged compound [(NC)Ru₂(<em>ap</em>)₄]₂(μ-1,4-C₆H₄). Chapter 3 highlights the synthesis and characterization of bis-aryl and bis-alkynyl Ru2(III,III) compounds, Ru₂(amtfmp)₄(Y)₂ (Y = -C≡CPh, -Ph), supported with the electron-withdrawing paddlewheel ligand amtfmp (amtfmp = 2-amino-3-(trifluoromethyl)pyridinate). </p> <p>Chapters 4 and 5 are focused on the synthesis and characterization of both mono- and bis-alkynyl unsymmetric compounds to study photo-induced electron transfer (PET) processes. Chapter 4 features as an introduction to the synthesis of these Ru(II)(dppm)₂ and Ru(II)(dppe)₂alkynyl compounds along with some material applications. Chapter 5 discusses the mono- and bis-alkynyl compounds based on Ru(II)(dppm)₂ and Ru(II)(dppe)₂ bridges that utilized a highly electron-withdrawing chromophore ‘acceptor’ ligand, NAP^R (R = isopropyl, mesityl), to generate the <em>B-A</em> (mono-alkynyl) and <em>D-B-A</em> (unsymmetric bis-alkynyl) compounds.</p>

The use of ligand in transition-metal catalysed reactions has had a considerable impact. The present manuscript aims at showing the influence of ligands in the palladium catalysed Suzuki-Miyaura cross-coupling reaction. In chapter one, the mechanism of this reaction will be described based on the numerous contribution published in the literature. It will be shown that the electronic and steric properties of the ligands have a huge repercussion on the catalytic activity of the metal. In the second chapter, the electronic and steric properties of the widely used Buchwald-phosphine ligand will be investigated. For this purpose, bis-carbonyl iridium(I) complexes were synthesized and their characterization allowed determining their TEP (Tolman electronic parameter) and their buried volume %V[subscript(bur)]. Then three next chapters of this thesis will focus on the syntheses and characterizations of new palladium complexes bearing N-heterocyclic carbenes (NHC). Their design was made in a view to obtain high activity in cross coupling reaction, particularly in the Suzuki-Miyaura cross coupling. Their activation under the catalytic conditions leads to the formation of palladium(0) species that can be mono- or bis-ligated. The influence of the ligand on the catalyst activity will be discussed. A palladium(II) precatalyst leading to mono-ligated active species will be described. Its activity in cross-coupling is very good, since activated and non-activated aryl chlorides could be coupled with aryl boronic acids at room temperature using low catalyst loadings. Unfortunately, the catalyst activity decreased with temperature. This result showed the fragility of the mono-ligated active species. In a view to obtain more robust catalysts that can perform high turnover numbers, new palladium(II) precatalysts bearing two ancillary ligands were developed. Mixed systems NHC- phosphites and NHC-phosphines are described. NHC-phosphites precatalysts displayed very good activity, but the phosphites are unfortunately sensitive to reaction conditions, limiting their role of active species shield. NHC-phosphine bearing complexes were highly active and could perform up to 10,000 turnovers with unactivated aryl chlorides. Very interestingly, these catalysts were also able to couple benzylchlorides and allyl chlorides with a wide range of boronic acids at very low catalyst loadings. These reactions had also the great advantage to proceed in aqueous solvents at very high substrate concentration. The activation mechanism of these complexes was investigated. Dichloropalladium(II) complexes were reduced under the catalytic conditions to lead palladium(0) species. Therein, it is shown that this reduction step was rate-determining in catalysis. Some palladium(0) intermediates xxiv were synthesized and showed good to excellent activities at low temperature under the exact same conditions. They displayed high reactivity towards oxygen and moisture and have to be handled under inert atmosphere. A particular complex had the ability to react with molecular dioxygen to form a stable peroxo-complex. Interestingly, this complex displayed excellent activity in water under aerobic conditions. This system was of great advantage since the reaction could be set up under air using cheap and user-friendly reagents displaying low toxicity. Moreover, the readily available distilled water used as solvent did not require prior degassing. Symmetrical and unsymmetrical bis-NHC palladium(0) complexes were successfully synthesized. They display excellent activity in the Suzuki-Miyaura cross coupling and turnover frequencies as high as 300 could be obtained at room temperature with unactivated arylchlorides and arylboronic acids. These complexes were also found excellent catalysts for the coupling of benzylchlorides with arylboronic acids. Mechanistic studies showed that no ligand dissociation occurred during the coupling suggesting as bis-ligated active species.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy