Graduate / 0485

Graduate / 0485

This thesis describes the synthetic, structural and reactivity studies of η- cycloheptatrienyl-molybdenum and -tungsten chemistry. Chapter 1 presents an overview of the chemistry of η-cycloheptatrienyl derivatives of transition metals, in particular group 6 metals. The functional group properties of the η-cycloheptatrienyl ligand are also discussed. Chapter 2 describes the synthesis of [Mo(η-C₇H₇)(η⁵-C₇H₉)] from Mocl₅ or [MoCl₄(thf)₂], which provides a convenient route to η-cycloheptatrienyl-molybdenum compounds, such as [Mo(η-C₇H₇)LX₂] and [Mo(η-C₇H₇)L₂X], where L = tertiary phosphines or acetonitrile and X = halogen, [NBu₄] [Mo(η-C₇H₇)I₃], [Mo(η-C₇H₇)(η- C₅H₄R)] (R = H or Me) and [Mo(η-C₇H₇)(η⁵-C₉H₇)]. The X-ray crystal structures of [Mo(η-C₇H₇)(MeCN)I₂], [NBu₄][Mo(η-C₇H₇))I₃] and [Mo(η-C₇H₇)(η-C₅H₄Me)] are presented. The compound [Mo(η-C₇H₇))(MeCN)I₂], mixed with Me₃SiCH₂MgCl, is a catalyst for ring-opening polymerisation of norbornene giving trans polymer exclusively. The electron-transfer complexes [Mo(η-C₇H₇)(η-C₅H₄Me)][tcne] and {[Mo(η-C₇H₇))(η- C₅H₅}₂[tcnq]} and the intercalation compound {ZrS₂[Mo(η-C₇H₇)(η-C₅H₄Me)]o.22} are also described. An extension of these synthetic pathways to tungsten is described in chapter 3. Reduction of WCl₆ with sodium amalgam in the presence of cycloheptatriene gives [W(η- C₇H₇)(η⁵-C₇H₉)], which is a precursor to the compounds [W(η-C₇H₇)(MeCN)I₂], [W(η- C₇H₇)(PMe₃)X₂] (X = Br or I), [W(η-C₇H₇)(dmpe)I], [W(η-C₇H₇)(η-C₅H₄R)] (R = H or Me) and [Mo(η-C₇H₇)(η⁵-C₉H₇)]. The [W(η-C₇H₇)(MeCN)I₂] / Me₃SiCH₂MgCI system is an active catalyst for ring opening polymerisation of norbomene. The electronic structures of [W(η-C₇H₇)(η-C₅H₄R)] (R= H or Me) are discussed on the basis of their He I and He II photoelectron spectra. The intercalation of [W(η-C₇H₇)(η-C₅H₄Me)] into ZrS<suv>2</sub> is also described. The magnetic properties of the 17-electron compounds [Mo(η-C₇H₇)(MeCN)I₂], [Mo(η-C₇H₇)(PMe₃)I₂], [W(η-C₇H₇)(MeCN)I₂], [W(η-C₇H₇)(PMe₃)I₂] and [W(η-C₇H₇) (PMe₃)I₂] are discussed in chapter 4. They behave as one-dimensional antiferromagnets which was suggested by magnetic model fittings and the crystal structure of [Mo(η-C₇H₇)(MeCN)I₂]. Chapter 5 comprises of two parts. The first part describes a new series of binuclear thiolato-bridged molybdenum complexes [(η-C₇H₃R¹₄)Mo(μ-SR²)₃ Mo- (η-C₇H₃R¹₄)][BF₄] (R¹ = H or Me; R² = Et, Pr, Bu, Ph or CH₂Ph). Dynamic NMR studies reveal that all of these complexes (except for R² = Ph) are fluxional due to inversion at the pyramidal sulfur centre. Cyclic voltammetric studies show that they undergo two reversible one-electron reductions. Second part of this chapter describes the new bridging-imido compound [(η-C₇H₇)Mo(μ-NAr)₂Mo(η-C₇H₇)] (Ar = 2,6- diisopropylphenyl). Chapter 6 discusses the η-l,2,4,6-tetramethylcycloheptatrienyl-molybdenum system. The new η-tetramethylcycloheptatriene molybdenum compounds [M'(η-C₇H₄Me₄- 1,3,5,7)],[M'(η-C₇H₄Me₄-l,2,4,6)] and [M'(η-C₇H₄Me₄-l,3,4,6)], M' = Mo(CO)₃, and new η-tetramethylcycloheptatrienyl-molybdenum compounds [M"(CO)₃]+, [M"(CO)₂C1], [M"(dmpe)Cl], [M"(η-C₆H₅Me)]+ and [M"(acac)(PPh₃)], M" = Mo(η- CC₇H₃Me₄-1,2,4,6), and [Mo(η³-C₇H₃Me₄-l,2,4,6)(dmpe)(CO)₂Cl] are described. Chapter 7 gives the experimental details for the work described in preceeding chapters. Appendix A presents characterising data for all the new compounds and previously unreported data for known compounds. Crystallographic details for the X-ray structure determinations and X-ray powder diffraction data are listed in Appendix B and C respectively.

Novel synthetic applications of ambident azo-anions derived from hindered hydrazones have been investigated. Reaction with electrophiles occurred predominantly at carbon as the N-addition pathway was sterically retarded. Trityl, diphenyl-4-pyridylmethyl (DPP) benzhydryl, and t-butyldiphenylmethyl (BDP) hydrazones of various aldehydes and ketones were prepared in good yields from the corresponding hydrazines and carbonyls in aqueous methanol. The lithium salts derived from trityl and DPP hydrazones, by treatment with methyl lithium at -55°C, reacted with aldehydes and ketones to generate azo-alkoxides. These could be diverted to alcohols,by sequential protonation and spontaneous homolysis (about -20°C) in the presence of ethanethiol, or to alkenes,by treatment with phosphorus trichloride at -78 G followed by azo-homolysis. The reactions enabled efficient reductive cross-coupling of aldehydes and ketones. The mechanism of the alkene forming reaction was investigated. Anions of benzhydryl hydrazones were found to react inefficiently by a G-addition pathway giving mainly N-addition products. Anions of BDP hydrazones conveniently gave excellent yields of azo-alkanes upon treatment with alkyl halides,but no products were obtained on reaction with carbonyl electrophiles. The azo-alkanes could be isolated and purified and acted as key intermediates for several synthetically useful transformations. Homolysis in refluxing benzene with thiophenol gave alkanes in good yields. Phenylselenenyl-, bromo-, and chloro-alkanes,and β-alkylstyrenes were generated when thiol was replaced by diphenyl diselenide, N-bromosuccinimide, N-chlorosuccinimide and β-nitrostyrene respectively. Treatment of the azo-alkanes with trifluoroacetic acid generated benzophenone alkylhydrazones. These were dissolved in ethanol with concentrated hydrochloric acid, thereafter hydrolysis yielded alkylhydrazines or treatment with hydrogen (1 atm., 50°C, 20h) over 10% Pd/C generated primary amines by a novel use of carbonyls as α-aminocarbanion equivalents.

This thesis reflects two main aims. Firstly, the synthesis and characterisation of a number of potential anion receptors was undertaken and their anion binding properties were assessed. In so doing, a second aim was fulfilled, namely a comparison of the various methods of detecting the bound anion, and quantifying the binding strength. Four techniques appear in this thesis; ¹H nuclear magnetic resonance, UV-visible spectroscopy, electrochemistry and luminescent emission. Quantitative titrations were performed and, where possible, stability constants estimated. Chapter One provides an introduction to some of the themes of molecular recognition and provides a brief overview of the literature associated with anion recognition. A Prologue describes the design of the receptors studied; they all incorporate a metal centre and appended amide groups which provide sources of hydrogen bonding. The molecules are mostly cationic and a combination of positive charge and hydrogen bonding constitutes the binding interaction. Chapter Two is concerned with receptors based on cobalticinium, [Cp₂Co]⁺ . A number of receptors are presented and are found to bind anions with stability constants typically in the range of 500-1000 dm³mol^-1 . Receptors involving more than one cobalticinium centre are found to bind much more strongly and, furthermore, variations in functional groups appended close to the proposed coordination site impart selectivity; dihydrogen phosphate is bound more strongly than chloride. It is also found that different techniques give different stability constants and comment is made on this phenomenon. Chapter Three examines the role of positive charge in anion binding and describes the synthesis and coordination properties of several neutral receptors. These molecules retain hydrogen bonding sites, and it is found that this is sufficient to bind anions, but the strength of the interaction is greatly reduced. Chapter Four introduces another system, based on RuL(bpy)₂²⁺ , where L is a 4,4'-amide disubstituted bpy. The strength of binding is an order of magnitude greater than the cobalticinium systems as detected by several methods including emission studies, which are very sensitive. Comparison with a neutral, rhenium-based receptor is made. A dihydrogen phosphate-selective luminescent sensor is also presented. The Epilogue identifies areas for future research. Specialised introductions and summaries are found at the beginning and end of each chapter.

Methylzinc tetrahydroborate, [MeZnBH₄], has been prepared by two routes and the structure of the solid determined by X-ray crystallography to reveal helical polymers in which MeZn and BH₄ units alternate. The latter functions as a bidentate ligand with respect to each of the adjacent metal atoms. Investigation by mass spectrometry and matrix isolation shows that the vapour consists of an equilibrium mixture of monomeric and dimeric species. The pattern of infrared bands for the monomer is characteristic of a bidentate BH₄ group, a finding consistent with the results of DFT calculations. Disproportionation into [Me₂Zn] and [Zn(BH₄)₂] is a common feature of the chemistry of methylzinc tetrahydroborate, although it has been possible to isolate and characterize the adduct [MeZnBH₄.SMe₂]. The reaction between [B₄H₁₀ and [Me₂Zn] in the gas phase affords colourless acicular crystals of [(MeZn)₂B₃H₇] in yields of ca. 10%. This compound has been characterized by chemical analysis and by NMR and vibrational spectroscopy. X-ray crystallography reveals that the product is a dimer, [(MeZn)₂B₃H₇]₂, featuring two distinct zinc environments. Two B₃H₇ZnNe ligands, formally derived from B₃H₈ by replacement of a µ₂-H by a µ₂-ZnMe unit, each function in a bis(bidentate) manner linking together two other MeZn centres through pairs of Zn-H-B bridges. The structures of several aluminium tetrahydroborates in the solid phase have been investigated by X-ray diffraction. The structure of dimethylaluminum tetrahydroborate has been shown to consist of helical polymeric chains in which Me₂-Al and BH₄ units alternate. Here, too, the BH₄ groups exhibit bidentate ligation with respect to each of the adjacent metal atoms, although the degree of interaction between the metal centre and the BH₄ group is somewhat less than in [MeZnBH₄ ]. Solid aluminium tris(tetrahydroborate) exhibits two phases with a transition temperature in the range 180-195 K. Each phase is made up of discrete Al(BH ₄ )₃ units, the principal differences relating to the packing of the individual molecules. In the a phase the Al(BH ₄ )₃ molecules display an angle of 78.2° between the AlB₃ and Al(µ-H)₂ planes and are disposed about a 2₁ crystallographic screw axis; in the ß phase the molecular units conform to D_3h symmetry. Dimethylindium octahydrotriborate, [Me₂ lnB₃ H₈ ], has been synthesized by the reaction between trimethylindium and tetraborane(10) and characterized by chemical analysis and by NMR and vibrational spectroscopy. X-ray diffraction of a single crystal reveals that the solid consists of [Me₂ lnB₃ H₈] units, although there is evidence of charge separation in the sense [Me₂ln]⁺[B₃ H₈ ]^- and of secondary interaction between terminal hydrogen atoms and adjacent indium centres. The infrared spectrum of the matrix-isolated vapour is consistent with a monomeric structure similar to that of [Me₂ AlB₃ H₈].

Experiments to measure (i) the reactivity of lithium peroxide and lithium oxide in ambient air as a function of relative humidity and reactant particle size, (ii) the solubility of lithium hydroxide and lithium hydroxide monohydrate in three alcohols, namely methanol, ethanol and 1 and 2-propanol, as a function of time and temperature, (iii) the efficiency of the production of lithium peroxide in alcohol medium as a function of the concentration of LiOH.H 2O in methanol, the concentration of hydrogen peroxide, the kind of alcohol, the kind of feed material, and temperature and the time of mixing, (iv) the analysis of the precipitates, (v) the temperature of the precipitate decomposition in isothermal and non-isothermal conditions in ambient and neutral conditions as function of time, (vi) the activation energy of the precipitate decomposition, (vii) the temperature of the lithium peroxide decomposition in isothermal and non-isothermal conditions as function of time and (viii) the activation energy of lithium peroxide decomposition were performed. / The purpose of the study was to gather the data necessary to evaluate the production of lithium peroxide, Li2O2, and subsequently lithium oxide, Li2O, to be used as a feed for a silicothermic reduction process for the production of metallic lithium. The proposed basis for the production of Li2O2 was the conversion of lithium hydroxide or lithium hydroxide monohydrate by hydrogen peroxide in an alcohol medium. Alcohols were chosen because they are members of a class of non-aqueous solvents that can selectively dissolve the anticipated contaminants while precipitating the desired products. / It was found that the addition of hydrogen peroxide to alcohol solutions containing lithium hydroxide monohydrate resulted in the formation of lithium peroxide as lithium hydroperoxidate trihydrate with eight adduct molecules of methanol, i.e., Li2O2•H2O 2•3H2O•8CH3OH and involved the peroxide group transfer. The optimum conditions for the production of lithium peroxide were found to be (i) the least water concentration in the system (ii) the use of the temperature lower than ambient temperature and (iii) fast separation of the precipitate and raffinate to prevent dissociation of the precipitate or dissolving into the raffinate. / The high solubility of LiOH.H2O and at the same time the low solubility of Li2CO3 and of Li2O2 in methanol resulted in selection of methanol as the best alcohol of those studied for the proposed method of Li2O2 production. It also yielded high purity lithium peroxide. The production of Li2O 2 using H2O2 (35 %wt) required an excess of hydrogen peroxide equal to 2.6 times the stoichiometric amount. / The thermal decomposition of the lithium hydroperoxidate trihydrate precipitate started with the rejection of the adduct methanol molecules, followed by co-evolution of H2O and H2O2 from the resulting Li 2O2•H2O2•H2O. The activation energy of the decomposition reaction of the precipitate was measured as 141 kJ/mol. At temperatures greater than 200°C, lithium peroxide was found to be very reactive with atmospheric air. However, in an argon atmosphere, it rapidly decomposed losing the majority of the oxygen atoms, followed by the gradual slow diffusion of oxygen gas absorbed on the lithium oxide.

No description available.

The synthesis and characterization of pyridinyl &alpha / -diimine Pd(II) complexes having a functionalized hydrocarbon attached to the imino nitrogen was performed. The catalytic activity of these complexes were then evaluated in the polymerization of ethylene and in the Heck coupling reaction of methyl acrylate with iodobenzene.<br /> <br /> Unconjugated &beta / -diimine complexes of palladium were also synthesized and their activities towards ethylene polymerization and the Heck coupling of methyl acrylate and iodobenzene also evaluated and compared to that of the &alpha / -diimine complexes. Three of the &alpha / -diimine complexes synthesized showed activity towards ethylene polymerization, these being the complexes bearing the allyl, styrene and phenol functionalities. &omega / -Carboxylato complexes which were also synthesized showed no activity towards ethylene polymerization.<br /> <br /> The polymer produced was found to be high density linear polyethylene with an average PDI of 2.54 with Mn values ranging between 3.42 and 6.90 x 10-5 and Mw values ranging between 6.05 and 17.6 x 10-5.<br /> <br /> The complexes bearing the allyl, styrene and phenol functionalities, as well as the &omega / -carboxylato complexes active in the Heck coupling reactions of methyl acrylate with iodobenzene. None of the unconjugated &beta / -diimine complexes prepared showed any activity towards ethylene polymerization even at high Al/Pd ratios. The activity of these complexes towards the Heck arylation reaction was comparable to that of the &alpha / -diimine complexes showing similar activities.

Copy of author's previously published article inserted. / Includes bibliographies / vi, 230 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis studies the B-cyclodextrins which are modified at the primary rim to incorporate an additional coordination or hydrophobic recognition site. The natural organic host, cyclodextrin and its chemically modified derivatives, are utilised as hosts for the inclusion of a range of guests. The study contributes to understanding the fundamental factors influencing selectivity of binding and the stability of the complexes formed when a guest is bound essentially at two recognition sites. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 1996