This Thesis describes the synthesis and reactivity of Group 5 imido and hydrazido complexes with tridentate, trianionic ligands. Various synthetic routes towards these hydrazido compounds were explored and in which several intermediates were synthesised and their chemistry was explored. The reactivity of the imido and hydrazido complexes with unsaturated and other small molecules was also studied. <b>Chapter One</b> provides a general introduction to tridentate pincer and tripodal ligands. The structure, synthesis and reactivity of Group 4 and 5 imido and hydrazido complexes is also reviewed. <b>Chapter Two</b> describes three different synthetic routes towards tantalum hydrazido complexes with tridentate, trianionic ligands. Synthesis, characterization and bonding analysis of the precursor dichloride species Ta(NN₂^SiMe3)Cl₂, which is used as starting material for two of the synthetic routes, is also described. The synthesis, characterization and bonding analysis of the tantalum dialkyl and alkyl-amido precursors prepared in the multistep route is also explored. <b>Chapter Three</b> describes the synthesis and characterisation of Group 5 imido complexes with tridentate, trianionic ligands of the type Li₃(NN₂^R) and Li₃(NNN^SiMe3). Reactivity studies of the imido complex Nb(NN₂iPr)(N^tBu)(py)₂ with unsaturated and other small molecules are also explored. <b>Chapter Four</b> describes the synthesis and characterisation of Group 5 hydrazido complexes with tridentate, trianionic ligands by two different synthetic routes, alongside a bonding analysis of the imido compounds M(NN₂^R)(N^tBu)(py)₂ and their hydrazido analogues M(NN₂^R)(NNPh₂)(L)_x. Reactivity studies of the hydrazido complex Nb(NN₂^iPr)(NNPh₂)(py)₂ with unsaturated and other small substrates are also described. <b>Chapter Five</b> presents full experimental procedures and characterising data for the new methodologies and complexes reported in this Thesis.

Doctor of Philosophy / Department of Chemistry / Stefan Kraft / Highly toxic aromatic halogenated compounds such as PCB’s, PCDF’s and PCDD’s act as persistent organic pollutants and can bio-accumulate. These compounds are highly stable to oxidation, reduction and thermal degradation. Current remediation technologies are expensive and can cause the formation of even more toxic byproducts. It is clear that an environmentally friendly and inexpensive remediation technology is required. Our goal was the synthesis of dehalogenation catalysts incorporating aromatic side arms for the pre-concentration of the substrates to the catalysts. We envisioned that aromatic side arms would allow the aggregation of catalyst and substrate to form a pre-complex that would enhance rates of dehalogenation. Rapid and stereochemically predictable synthesis of N and C functionalized nickel cyclam complexes were a priority for this project. Synthesis of N-functionalized cyclam molecules and subsequent metal incorporation proceeds smoothly to form trans(III) nickel cyclam complexes. However longer reaction times, initiation periods and short catalyst lifetimes made these complexes unsuitable for long-term study. Cyclization of dipeptides and tetrapeptides using a metal template in basic conditions led to the formation of cyclopeptide nickel complexes with stereochemistry retained from the peptide precursors. Free cyclopeptides could be isolated from the nickel complexes by treatment with HCl. Cyclopeptides are reduced to the cyclam molecules via a LAH reduction in low to moderate yields. Nickel incorporation into the cyclam molecules produced C-functionalized nickel catalysts with stereochemical integrity maintained throughout the synthesis. Intermolecular CH-π interactions can be seen in the solid state for the nickel cyclam complexes with aromatic side arms. Reduction data show that the C-functionalized catalysts do not show improved rates of reduction for several aromatic substrates but small rate enhancements are observed for the reduction of chloronaphthalene over the unfunctionalized catalyst.

published_or_final_version / Chemistry / Master / Master of Philosophy

In this dissertation, catalytic C-F bond activation mediated by alumenium and silylium species, improved methods for the synthesis of highly chlorinated carboranes and dodecaborates, new type of P2Si= pincer silylene Pt complexes and PBP pincer Rh complexes are presented. In Chapter II, the design and synthesis of P2Si= and PBP ligand precursors is described. BrC6H4PR2 is shown to be a useful building block for PXP type of ligands with o-arylene backbone. RLi reagents displayed high chemoselectivity towards electrophiles, such as Si(OEt)4 and BX3 (X = Hal). In Chapter III, new chlorination methods to synthesize [HCB11Cl11]- and [B12Cl12]2- are presented. [HCB11Cl11]- was obtained via reactions of Cs[HCB11H11] with SbCl5 or via reactions of Cs[HCB11H11] with Cl2 in acetic acid and triflic acid. Heating Cs2[B12H12] in mixtures of SO2Cl2 and MeCN led to the isolation of Cs2[B12Cl12] in high yield. In Chapter IV, Et2Al[HCB11H5Br6] or Ph3C[HCB11H5Br6] were shown to be robust catalysts for sp3 C-F bond activation with trialkylaluminum as the stoichiometric reagent. Trialkylaluminum compounds were also shown to be able to be used as “clean-up” reagent for the C-F bond activation reactions, which led to ultra high TON for the catalytic reactions. In Chapter V, a series of (TPB)M complexes (M = Ni, Pd, Pt) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The resulting metal complexes displayed strong dative M→B interaction and unusual tetrahedral geometry for four-coordinate 16ē species, due to the cage structure of the ligand. In Chapter VI, (PSiHP)PtCl was synthesized via the reaction of the ligand precursor and Pt(COD)Cl2, which was used to obtain a series of (PSiHP)PtX complexes(X= I, OTf, Me, Ph, Mes). After hydride abstraction by Ph3C[HCB11Cl11], the X ligand (X= I, OTf, Me, Ph) migrated from the Pt center to silicon center to give a cationic pincer silyl species. The migration was not observed when mesityl was used as the X ligand, which resulted in the first known pincer complex with central silylene donor. Our approaches towards PNP pincer boryl Rh complexes were summarized in Chapter VII. (PBPhP)Rh pivalate complex underwent C-Ph bond activation to yield the pivalate-bridging Rh borane complex.

La thèse se concentre sur la synthèse et la caractérisation de nouveaux complexes de manganèse comme alternative possible aux complexes de gadolinium, actuellement les agents de contraste de choix pour l’Imagerie par Résonance Magnétique (IRM). Dans cette perspective, nous nous sommes intéressés à trois groupes de ligands pentadentés pour la complexation de Mn2+. Des nombres de coordination de 6 ou 7 ont été déterminés par cristallographie pour ces complexes, permettant la coordination d’une ou deux molécules d’eau en première sphère de coordination de Mn2+. La stabilité thermodynamique de ces complexes est plus faible que celle de complexes polyaminocarboxylates et leur dissociation est très rapide comparée à [Mn(nota)] et [Mn(dota)]2-. Seuls les complexes de Mn2+ avec des ligands macrocycliques à 12 atomes sont oxydés en Mn3+ à l’air. Les relaxivités des complexes bishydratés sont deux fois plus élevées que celles des complexes monohydratés et elles sont comparables à celles des agents de contraste commerciaux. Les données de RMN d’17O mesurées à différentes températures ont montré que l’échange d’eau peut être lent, intermédiaire, ou rapide selon le ligand. Les mesures à hautes pressions ont confirmé que le mécanisme d’échange est de type dissociatif pour les complexes avec un nombre de coordination de 7 et de type associatif pour les complexes avec un nombre de coordination de 6. Les petits anions bidentés endogènes peuvent remplacer une molécule d’eau dans les complexes bishydratés de macrocycles pentaazotés à 15 atomes, alors que pour les autres soit le complexe se décompose, soit il n’y a pas d’influence. / The thesis is focused on the synthesis and characterization of novel manganese complexes as alternative to Gd3+ chelates which are wide-spread contrast agents in Magnetic Resonance Imaging (MRI). In this perspective, three structurally different groups of pentadentate ligands for Mn2+ complexation have been investigated. Coordination numbers of 6 or 7 were determined in the crystal structure of the Mn2+ complexes enabling one or two water molecules in the first sphere. The thermodynamic stability of the chelates is lower than that of polyaminocarboxylate complexes and their dissociation is very fast in comparison to [Mn(nota)] and [Mn(dota)]2–. Only Mn2+ complexes with 12- membered ligands undergo oxidation in air to Mn3+ species. The proton relaxivities of the bishydrated complexes are two times higher than those for monohydrated complexes and are comparable to those of commercial contrast agents. Variable-temperature 17O NMR data revealed that the water exchange varies from slow to intermediate or to extremely fast, depending on the ligand. High-pressure 17O NMR measurements confirmed dissociative water exchange mechanism on complexes with CN = 7 and associative mechanism on complexes with CN = 6. Small endogenous bidentate anions are capable of replacing only one water molecule in the bishydrated complex with the 15-membered pentaaza ligand (L2), while in other cases the complex is decomposed or no influence is observed.

Guo-cong Guo. / "June 1999." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Chapter 1 focuses on the computational study of Zr(CH2Ph)4 and chapter 2 discusses synthesis, characterization and density functional study of 2-imidazolethione. Chapters 3 - 6 describe the synthesis, structural characterization several multidentate tripodal ligands, namely tris(mercaptoimidazolyl)-hydroborato ligand, [TmR], tris(2-pyridylseleno)methyl ligand, [Tpsem], bis(2-pyridonyl)(pyridine-2-yloxy)methyl ligand, [O-poBpom] and allyl-tris(3-t-butylpyrazolyl)borato ligand, [allylTpBut], and their application to main group and transition metals. Chapter 1 describes the analysis of a monoclinic modification of Zr(CH2Ph)4 by single crystal X-ray diffraction, which reveals that the Zr-CH2-Ph bond angles in this compound span a range of 25.1°; that is much larger than previously observed for the orthorhombic form (12.1°;). In accord with this large range, density functional theory calculations demonstrate that little energy is required to perturb the Zr-CH2-Ph bond angles in this compound. Furthermore, density functional theory calculations on Me3ZrCH2Ph indicate that bending of the Zr-CH2-Ph moiety in the monobenzyl compound is also facile, thereby demonstrating that a benzyl ligand attached to zirconium is intrinsically flexible, such that its bending does not require a buffering effect involving another benzyl ligand. Chapter 2 describes the structure of 1-t-butyl-1,3-dihydro-2H-benzimidazole-2-thione which has been determined by X-ray diffraction. The compound exists in the chalcogenone form instead of chalcogenol form, which is similar to its oxo and selone counterparts. Comparison of 2-imidazolone, 2-imidazolethione and 2-imidazoleselone compounds shows that two N-C-E bond angles in the chalcogenone forms are not symmetric. This trend can be reproduced by density functional theory calculations. Additionally, H(mbenzimBut) has intermolecular hydrogen bonding interactions, whereas its selenium counterpart does not. The C-E bond lengths of 2-imidazolone, 2-imidazolethione and 2-imidazoleselone compounds are intermediate between those of formal C-E single and double bonds, which is in accord with the notion that zwitterionic structures that feature single C+-E- dative covalent bonds provide an important contribution in such molecules. Furthermore, NBO analysis of the bonding in H(ximBut) derivatives demonstrates that the doubly bonded C=E resonance structure is most significant for the oxygen derivative, whereas singly bonded C+-E- resonance structures dominate for the tellurium derivative. This result appears to be counterintuitive, based on the fact that it opposes the trend that one would expect on the basis of electronegativity difference, however, studies on XC(E)NH2 derivatives provide solid support for it. In this regard, the C~E bonding in these compounds is significantly different to that in chalcogenoformaldehyde derivatives for which the bonding is well represented by a H2C=E double bonded resonance structure. Chapter 3 describes the computational study on [TmMeBenz] anion and the synthesis and characterization of [TmButBenz]Na, [TmButBenz]Tl and [TmButBenz]Tl. It is worth noting that the two thallium compounds are the first structurally characterized monovalent monomeric [TmR]Tl complexes. Chapter 4 describes the synthesis and characterization of a few [TmR]M (M = Ti, Zr, Hf) complexes, including (i) Cp[TmBut]TiCl2 and Cp[TmBut]ZrCl2, which are analogues of Cp2TiCl2 and Cp2ZrCl2; (ii) [TmBut]Zr(CH2Ph)3 and (iii) [TmBut]Hf(CH2Ph)3 and [TmAd]Hf(CH2Ph)3, which are the first structurally characterized [TmR]Hf complexes. Chapter 5 describes two multidentate, L3X type ligands, which feature [CN3] and [CNO2] donors, namely tris(2 pyridylseleno)methane, [Tpsem]H, and bis(2-pyridonyl)(pyridin-2-yloxy)methane, [O-poBpom]H. They have been synthesized, characterized, and employed in the synthesis of zinc and cadmium complexes. Chapter 6 describes the synthesis and structural characterization of a new [Tp] ligand featuring an allyl substituent on the central boron atom, namely [allylTpBut]Li is reported. The compound reacts steadily with CH3CH2SH under 350 nm UV light via a thiol-ene click reaction. The resulting [CH3CH2S(CH2)3TpBut]Li complex can further react with metal halide. For example, the reaction of [CH3CH2S(CH2)3TpBut]Li with ZnI2 produced [CH3CH2S(CH2)3TpBut]ZnI at room temperature. This study provides a simple model on the immobilization of [Tp] metal complexes to the polymer chains with -SH terminals.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 185-195).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 99-107).

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Naresh Dalal, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (Jan. 19, 2005). Includes bibliographical references.