1,721,118 research outputs found
Hybrid Solid-State Hydrogen Storage Materials
No full textThis thesis investigates the chemistry of ammonia borane (NH₃BH₃) relevant to the development of hydrogen storage systems for vehicular applications.
Because of its high hydrogen content and low molecular weight ammonia borane has the potential to meet stringent gravimetric hydrogen storage targets of >9 wt%. Two of the three moles of H₂ in ammonia borane can be released under relatively mild conditions, with the highest gravimetric yield obtained in the solid-state. However, ammonia borane does not deliver sufficient H₂ at practical temperatures and the products formed upon H₂ loss are not amenable to regeneration back to the parent compound.
The literature synthesis of ammonia borane was modified to facilitate large scale synthesis, and the deuterated analogues ND₃BH₃ and NH₃BD₃ were prepared for the purpose of mechanistic studies.
The effect of lithium amide on the kinetics of dehydrogenation of ammonia borane was assessed by means of solid-state reaction in a series of specific molar ratios. Upon mixing lithium amide and ammonia borane, an exothermic reaction ensued resulting in the formation of a weakly bound adduct with an H₂N...BH₃-NH₃ environment. Thermal decomposition at or above temperatures of 50◦C of this phase was shown to liberate >9 wt% H₂. The mechanism of hydrogen evolution was investigated by means of reacting lithium amide and deuterated ammonia borane isotopologues, followed by analysis of the isotopic composition of evolved gaseous products by mass spectrometry. From these results, an intermolecular multi-step reaction mechanism was proposed, with the rates of the first stage strongly dependent on the concentration of lithium amide present. Compounds exhibiting a BN₃ environment (identi-fied by means of solid-state ¹¹B NMR spectroscopy) were formed during the first stage, and subsequently cross link to form a non-volatile solid. Further heating of this non-volatile solid phase ultimately resulted in the formation of crystalline Li₃BN₂ - identified by means of powder X-ray diffractometry.
This compound has been identified as a potential hydrogen storage material due to its lightweight and theoretically high hydrogen content. It may also be amenable to hydrogen re-absorption.
The LiNH₂/CH₃NH₂BH₃ system was also investigated. Thermal decomposition occurred through the same mechanism described for the LiNH₂/NH₃BH₃ system to theoretically evolve >8 wt% hydrogen. The gases evolved on thermal decomposition were predominantly H₂ with traces of methane detected by mass spectrometry
Synthesis, Characterisation and Applications of Novel Ionic Liquids.
No full textA series of novel phosphinate-based ionic liquids have been synthesised using various organic phosphorus acids, such as mono-n-octylphosphinic acid (octylPO₂H₂), mono-n-hexylphosphinic acid (hexylPO₂H₂), di-n-octylphosphinic acid ((octyl)₂PO₂H), di-n-hexylphosphinic acid ((hexyl)₂PO₂H) and bis(2,4,4-trimethylpentyl)phosphinic acid ((TMP)₂PO₂H), by reaction with tetrabutylphosphonium hydroxide (Bu₄POH), tetrabutylammonium hydroxide (Bu₄NOH), pyridine (py) and triethylamine (Et₃N). Reactions simply involve neutralizing the organophosphorus acids with bases. The only byproduct, water, and excess amine, py/Et₃N can be easily removed under vacuum (Chapter 2).
Some of the physical and chemical properties of these ionic liquids have been characterized by NMR, ES-MS, TGA, UV-Visible spectroscopy etc. The formed tetraalkylphosphonium/tetraalkylammonium phosphinate ionic liquids are viscous, hygroscopic liquids, but are more thermally stable than trialkylammonium and pyridinium analogues. For example, for the most stable ionic liquid, [Bu₄P][(octyl)₂PO₂], its onset temperature of decomposition in thermal gravimetric analysis (TGA) is 358 °C (Chapter 2).
One of the applications of these novel phosphinate-based ionic liquids has been investigated. Au(0), Rh(0) and Ir(0) nanoparticles have been prepared in some of these phosphinate-based ionic liquids as a media and (or) reducing agents and have been characterized by SEM, TEM, Zetasizer, UV-Visible spectroscopy and IR spectroscopy. In general, the average particles size of Au(0), and Ir(0) were ca. 25 nm, but some of the particles average size formed was less than 2 nm, such as Rh(0) and Ir(0) nanoparticles formed in [Bu₄P][(octyl)₂PO₂] or [Bu₄P][(TMP)₂PO₂]. Generally, these phosphinate-based ionic liquids are good media to prevent nanoparticle aggregation (Chapter 3)
The Composition of Arylstibonic Acids
No full textThis thesis describes a detailed ESI-MS investigation into the arylstibonic acids, organo-antimony-containing compounds that are currently of interest as anticancer reagents. Four arylstibonic acids, of nominal formula RC6H4SbO3H2 [R = p-chloro-, p-tolyl-, p-nitro- and α-naphthyl-] were synthesised, and a further eight archival samples from the National Cancer Institute Repository were obtained for use in the project. Results indicate clearly that the acids exist as polyoxometalate aggregates [H8(RSb)12O28], rather than monomeric species, in both the solid state and in acetonitrile solution, thus resolving a century-old debate concerning the nature of their molecular composition. Variations in solvent, time in solution and pH have also defined the stability of these aggregates under different conditions. Synthesis of arylstibonic acids by traditional methods (pre-1940) has been shown to lead to products contaminated with cations present during their preparation. An improved method of synthesis has been devised, and the crystal structure of an intermediate in the synthesis of these acids, [C6NH6][p-O2NC6H4SbCl5], is reported. Salts of arylstibonic acids with a range of cations were investigated by ESI-MS and shown to form a diverse family of polyoxostibonates with nuclearities including Sb12, Sb14 and Sb16. Crystal structures containing some of these aggregates, verified through parallel studies with collaborators, are described. Preliminary study of mixed polyoxometalates (Sb/As) showed a strong tendency to form As4Sb2 species but these could not be fully characterised
Gold(I) complexes and co oxidation catalysts
Get PDFIsonitrile gold(I) nitrates, (RNC)AuNO₃ (R = Buᵗ, Et or Xy) have been prepared and fully characterised. These join the rare set of gold(I) species exhibiting ligation to oxygen and are the first examples of gold(I) bonded to both carbon and oxygen. Molecular aggregations of the monomeric units were revealed by X-ray crystal structure determinations. The aggregations are the result of secondary Au--Au interactions. These interactions are also apparent in the structures of the analogous complexes (RNC)AuCl (R = Et or Xy), which were characterised for comparative purposes.
(EtNC)AuCl and (BuᵗNC)AuNO₃ formed zig-zag chain structures from which the other unprecedented structures can be derived. (EtNC)AuNO₃ formed a concertinaed chain, (XyNC)AuNO₃ (1) a compressed chain and (XyNC)AuCl a tetrameric chain. The formations of these supramolecular motifs are attributed to various steric and electronic ligand influences on the inherent Au--Au attraction. In addition, intermolecular π-π contacts were observed for the (XyNC)AuX (X = Cl or NO₃) structures.
In each instance, the Au--Au interactions for (RNC)AuNO₃ were significantly shorter than those of the analogous (RNC)AuCl structure. The results demonstrated that the non-polarisable nitrate anion enhances the Au--Au attraction. This is contrary to previous theoretical calculations, which predict that soft anions enhance the Au--Au attraction. The structure of the ionic [(XyNC)₂Au]⁺NO₃- complex was also characterised. This did not exhibit Au--Au contacts; the packing structure was instead based on infinite π-π stacking.
The potential of gold(I) complexes as precursors to supported gold catalysts was assessed. The complexes were adsorbed (from a solution phase) onto transition metal oxide supports which were subsequently vacuum dried and calcined. Scanning Electron Microscopy (SEM) revealed a range of gold particle sizes on the calcined materials. The extent of gold dispersion was dependent on the chemical properties of the complex employed.
The use of the stable (Ph₃P)AuCl, (Ph₃P)AuMe and (BuᵗNC)AuCl complexes resulted in relatively large gold particles (20-200 nm). In the case of (Ph₃P)AuMe, metallic gold crystals were observed. Under ambient conditions these materials were inactive for CO oxidation. Under the same testing conditions, efficient catalytic CO oxidation was observed over materials prepared by using the unstable (BuᵗNC)AuNO₃ complex as a precursor. The gold particles on the active catalyst were too small to be resolved by SEM.
The observed CO oxidation activity was proposed to be a two-component catalytic reaction involving gold nano-particles in intimate contact with a reducible oxide support. Reactant inhibition, which is commonly observed for catalysts with inert supports, is avoided in this system. This form of catalysis has received considerable recent attention for the CO oxidation reaction and provides guidance for attempts to enhance other heterogeneous catalytic processes
Polymetallic Silyl-Iron and -Ruthenium Compounds
No full textThe synthesis of iron and ruthenium compounds which contain either end-capped silyl units Fe-Si-Si-Fe or the linear sequence Si-Ru-Ru-Si respectively were explored.
(I) (II) (III)
End-capped iron species, e.g. I, were prepared using literature methods and two new related iron containing silyl species II and III were synthesised. These were prepared as model compounds for comparison with polymeric analogues.
(IV) (V)
Ruthenium silyl species of the type IV that maintain metal - metal bonding have been prepared. As an extension to this work inorganic polymeric species such as V were synthesised using the same preparation techniques.
The polymeric compounds were difficult to characterise as they were unable to be chromatographed or crystallised therefore, all data was from crude mixtures. Spectroscopic techniques involved FT - IR, ESMS, LDI-TOF and NMR spectroscopy. ESMS was an ineffective technique for the polymeric compounds however, LDI-TOF mass spectrometry gave broad curves with an average molecular weight ranging from 60,000 to 200,000 for different preparations.
Flexible siloxanes such as HSiMe2OSiMe2OSiMe2H gave molecular cluster derivatives with bridging ligands rather than polymers
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Some metallacyclic complexes of the late transition metals
Get PDFThe principal aim of this thesis is the synthesis and characterisation of four-membered metallacyclic complexes. Reactions of square-planar palladium(II), platinum(II) and gold(III) dihalide complexes with a variety of amides, some in the presence of silver(I) oxide are discussed.
Chapter one reviews the literature of small-ring metallacyclic chemistry, in particular the synthesis of four-membered metallacycles, as they are, in the main, the complexes that are further reported throughout the remainder of the thesis.
Chapter two reports the synthesis of four-membered metallalactam complexes [M{N(Ph)C(O)CHC(O)Ph}L₂] (2.11 - 2.15) formed from the reactions of square-planar L₂MCl₂ complexes [M = Pt, Pd, L = PPh₃, L₂ = 1,5-cyclooctadiene (COD), 1,2-bis(diphenylphosphino)ethane (dppe), 2,2’-bipyridine (bipy)] with 2-benzoylacetanilide [PhC(O)CH₂C(O)NHPh] in the presence of silver(I) oxide. The X-ray crystal structure of [Pd{N(Ph)C(O)CHC(O)Ph}(bipy)].CH₂Cl₂ (2.14.CH₂Cl₂) was determined to confirm the geometry of the compounds. The reactions of acetoacetamide [NH₂C(O)CH₂C(O)CH₃] with cis-[PtCl₂ (PPh₃)₂], [PtCl₂(dppe)] and [PdCl₂(bipy)] (2.16 - 2.18) in the presence of silver(I) oxide are also discussed.
Chapter three describes the isolation and characterisation of a platinum(II)-amidate complex, believed to be the first characterised intermediate in silver(I) oxide mediated reactions. For short reaction times the complex cis-[Pt{N(C(O)CH₂CN)(CO₂Et)}Cl(PPh₃)₂] (3.4) can be isolated from the reaction mixture of cis-[PtCl₂(PPh₃)₂] with N-cyanoacetylurethane [NCCH₂C(O)NHCO₂Et] in the presence of silver(I) oxide. For long reaction times this synthesis is known to afford the four-membered metallalactam [Pt{N(CO₂Et)C(O)CHCN}(PPh₃)₂].
Chapter four details the synthesis and characterisation of four-membered gold(III) lactam complexes. A series of metallalactam complexes were characterised from the reaction of [LAuCl₂] [L = {C₆H₃(CH₂NMe₂)-2-OMe-5} or {C₆H₄(CH₂NMe₂)-2}] with N-cyanoacetylurethane, 2-benzoylacetanilide, acetoacetanilide or acetoacetamide in the presence of silver(I) oxide. A representative of these gold(III) metallacycles, [{C₆H₄-CH₂NMe₂-2}Au{N(Ph)C(O)CHC(O)CH₃}] (4.13), was structurally characterised. A novel and unprecedented dimerisation occurred with [{C₆H₃-CH₂NMe₂-2-OMe5}Au{N(CO₂Et)C(O)CHCN}], that formed an eight-membered metallacycle (4.15) which was characterised by an X-ray diffraction study.
The reactions of cis-[PtCl₂(PPh₃)₂] with either cyanoacetic acid or phenoxyacetic acid in the presence of silver(I) oxide are reported in chapter five. The reaction of phenoxyacetic acid with cis-[PtCl₂(PPh₃)₂] was found to form the simple platinum(II) bis(carboxylate) complex, cis-[Pt(O₂CCH₂OPh)₂(PPh₃)₂] (5.9). Conversely, cyanoacetic acid undergoes a novel decarboxylation reaction which results in the formation of the platinum(II) bis(alkyl) complex cis-[Pt(CH₂CN)₂PPh₃)₂] (5.7). The X-ray crystal structures of these two complexes are described.
Chapter six discusses the triethylamine-mediated syntheses of four-membered metallalactam complexes. The reactions of cyanoacetylurea [NH₂C(O)NHC(O)CH₂CN] with cis-[PtCl₂(PPh₃)₂], [PtCl₂(COD)], [PtCl₂(dppe)] and [PdCl₂(dppe)] in the presence of triethylamine and details of their characterisation are described. One complex, cis-[Pt{N(C(O)NH₂)C(O)CHCN}(PPh₃)₂] (6.5), was structurally characterised and was found to crystallise as an H-bonded dimer. The reactions of N-cyanoacetylurethane, 2-benzoylacetanilide and acetoacetanilide with cis-[PtCl₂(PPh₃)₂] in the presence of silver(I) oxide are known to give well-characterised four-membered metallalactam complexes. The results of the reactions of these compounds when reacted under similar conditions, but with triethylamine as the base and halide abstractor, are also discussed.
Chapter seven describes a selection of four crystal structures. The X-ray structure of the first coordinatively saturated iridaureylene complex, [Ir{N(Me)C(O)NAc}(Cp*)(PPh₃)] (7.4), which is isoelectronic with four-membered metallalactam complexes, is described. The complex was found to adopt a “bar-stool” geometry. The structures of the complexes, [Rh{O₂CC₆H₄-S-2}Cp*]₂ (7.8) and [Ru{O₂CC₆H₄-S-2}(p-cymene)]₂ (7.9) were studied and found to be dimeric compounds. The complexes were found to adopt a pseudo-octahedral geometry, with a three-coordinate, bridging thiolate sulfur. The fourth structural analysis was that of the novel chelation product of cis-[Pt{NCH₂CH₂C(O)}₂(PPh₃)₂] with uranyl nitrate [UO₂(NO₃)₂]. The complex was found to form an eight-membered heterocycle (7.15), with the platinum bis(lactam) complex coordinating to the uranium via the lactam oxygen atoms
Electrospray-friendly ligands for the mass spectral analysis of transition-metal complexes
Get PDFThe key aim of this project was to develop the concept of electrospray-friendly ligands as a new ionisation method for the analysis of neutral metal complexes by electrospray mass spectrometry (ESMS). This involved introducing active functional groups into traditional ligands which do not otherwise undergo chemical ionisation under ESMS conditions.
Electrospray-friendly ligands (as illustrated above for PPh₃ derivatives) were incorporated into a series of metal carbonyl complexes of Mo, Fe and Ru, metal halide complexes of Pd, Pt and Au, and a number of zero-valent complexes of Pt and Pd. All carbonyl complexes with ES-friendly phosphine, arsine and stibine ligands ionised by protonation, yielding strong [M + H]⁺ ions as the only signals in the spectrum. The metal halide complexes followed the known halide-loss mechanism. Pt(0) and Pd(0) complexes did not require functionalised ligands, as their PPh₃ derivatives already gave [M +H]⁺ ions. Mo and W carbonyl complexes of the two ‘naturally’ electrospray friendly ligands tpa (tpa = 1,3,5-triaza-7-phosphaadamantane) and tcep [tcep = tris(2-cyanoethyl)phosphine] could also be studied readily by ESMS. While all tpa complexes gave [M + H]⁺ ions, complexes of tcep preferred ionisation by NH₄⁺. The ionisation efficiencies of selected ligands and complexes are discussed.
Thiolate complexes of Ni, Pd, Pt, Au and Hg were prepared using the ligands SC₆H₄OMe-p (S*) and p-SC₅H₄N (S•), but only the S•-complexes reliably underwent the protonation-type mechanism. The Cd-thiolate complexes [Cd₄(SPh)₁₀]²⁻, [S₄Cd₁₀(SPh)₁₆]⁴⁻ and [S₄Cd₁₀(SPh)₂₈]²⁻ underwent rapid ligand exchange with S*, but yielded insoluble products with S•. The complexes [Pt₂(μ-S)₂(L)₂] (L = PPh₃, P*, P**, P***. P•. As***¹) were prepared, and by means of ESMS, aspects of ligand exchange as well as reactivity towards other metal centres were investigated.
Isonitrile derivatives of [Fe₃(CO)₁₂] and [Ru₃CO)₁₂] were prepared by ligand exchange with CNPh, CNC₆H₄OMe-p (CNPh*) and tosylmethylisocyanide. Substitution was observed for up to six CO ligands. Pyrolysis of [Fe₃(CO)₁₁(L)] and [Fe₃(CO)₁₀(L)₂] (L =CNPh, CNPh*) led to the products [Fe₃(CO)₉(μ₃ - η²-L)] and [Fe₃(CO)₈(μ₃-η²-L) (L)], respectively. All complexes could be studied by ESMS as their [M + H]⁺, [M + MeO]⁻ or [M – H]⁻ ions, depending on the exact nature of the analyte. [Fe₃(CO)₁₀(CNPh)₂] was characterised structurally (below) and revealed an unprecedented substitution pattern, together with unexpected partial disorder in the metal framework.
Detection by ESMS of products of the type [Ru₄(CO) ₁₄₋ₙ(L)ₙ] (L = CNPh, CNPh*; n =2-4) in the reactions with ruthenium carbonyl led to the isolation and structural characterisation of [Ru₄(CO)₁₂(CNPh)₄], which is the only fully characterised isonitrile derivative of [Ru₃(CO)₁₂] with four metal atoms and exhibits an unusual imine-type bonding mode for the bridging isonitrile ligands.
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¹As*** = As(C₆H₄OMe-p)
Reactions of cyclomanganated compounds
Get PDFThis thesis describes novel reactions of cyclomanganated compounds of the general form shown below. The ligand is bonded by a metal-carbon σ-bond, with X acting as a donor atom to form the chelate ring. The organic ligands were derived from aryl and heteroaryl ketones, chalcones, dienones and azabutadienes.
A preliminary investigation has previously been undertaken into the reaction of carbon disulfide with some orthomanganated aryl ketones. In the present study these reactions were further investigated, with the isolation of new η2-S, S-dithiocarboxylate complexes, e.g. 46. In other cases the reaction of carbon disulfide with cyclomanganated compounds afforded the novel Mn4 species 50 in low yield.
The reactions of orthomanganated acetyl-aryl compounds with organic isocyanides (C≡NR) afforded a number of novel compounds. For example η2-(2-acetylphenyl)-tetracarbonylmanganese (79) afforded four different types of products depending on the isocyanide; tert-butyl isocyanide produced 82, ethyl isocyanide produced 95 and 96, and 4-methoxyphenyl isocyanide produced 98 and 99.
With orthomanganated 2-acetylthiophene, CNBut gave the quinone species 88 and 89,which showed high anti fungal and antitumor activity.
Cyclomanganated dienones (e.g. 127) were previously known to react with alkynes to give either (η5-pyranyl)Mn(CO)3 (e.g. 130) or (η5-oxocycloheptadienyl)Mn(C0)3 (e.g.129) products. The factors influencing which product is formed were more systematically investigated and a deuterium-labelling experiment was used to probe the1,2-phenyl shift that occurs for the (η5-oxocycloheptadienyl)Mn(C0)3 products .
A preliminary investigation of the reactions of 4-phenyl-1-(4-tolyl)-l-azabuta-1, 3-diene(TAD) with PhCH2Mn(CO)5 and unsaturated substrates including phenyl acetylene, methyl acrylate, PhNCO, ButNC and carbon disulfide is also described. A number of novel compounds were produced, including 169 from the reaction involving PhNCO.
In contrast η2-(5-methoxy-2-acetylphenyl)tetracarbonylmanganese with ally1 isothiocyanate gave simply 2-allyl-4-methoxyacetophenone by allylation of the orthomanganated starting compound. Allyl bromide behaved similarly. However, allyl bromide and ethyl bromide when reacted with the cyclomanganated chalcone 54 gave furanone products (e.g. 190 and 191). An oxidative addition and reductive elimination mechanism was proposed to explain this reaction.
Among others, the crystal structures of 50, 89 and 130 were determined
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