published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

This thesis reports on the development and expansion of reliable synthetic di-and multi-tin precursors for the assembly of oligomeric organotin-oxo compounds in which the shape, dimension and tin nuclearity can be controlled. The reaction of polymeric diorganotin oxides, (R2SnO)m (R = Me, Et, n-Bu, n-Oct, c-Hex, i-Pr, Ph), with saturated aqueous NH4X solutions (X = F, Cl, Br, I, OAc) in refluxing 1,4-dioxane afforded in high yields dimeric tetraorganodistannoxanes, [R2(X)SnOSn(X)R2]2, and in a few cases diorganotin dihalides or diacetates, R2SnX2. This method appears to be particularly good for the synthesis of halogenated tetraorganodistannoxanes but a less suitable method for the preparation of dicarboxylato tetraorganodistannoxanes. Identification of [R2(OH)SnOSn(X)R2]2 (R = n-Bu; X = Cl, Br) and [R2(OH)SnOSn(X)R2][R2(X)SnOSn(X)R2] suggest a serial substitution mechanism starting from [R2(OH)SnOSn(OH)R2]2. A series of α, ω -bis(triphenylstannyl)alkanes, [Ph3Sn]2(CH2)n (n = 3-8, 10, 12) and some of their derivatives were synthesised and characterised. These α, ω-bis(triphenylstannyl)alkanes, [Ph3Sn]2(CH2)n were converted to the corresponding halides [R(Cl)2Sn]2(CH2)n (R = CH2SiMe3) and subsequently to the polymeric oxides {[R(0)Sn]2(CH2)n}m. Reaction of {[R(O)Sn]2(CH2)n}m with [R(Cl)2Sn]2(CH2)n. (n = 3, n' = 4 and n = 4, n' = 3) in toluene at 100°C results in a mixture of symmetric and asymmetric double ladders, where different spacer chain lengths (n and n') provide the source of asymmetry. The coexistence at high temperature of separate 119Sn NMR signals belonging to symmetric and asymmetric double ladders suggests an equilibrium that is slow on the 119Sn NMR time scale and the position of which is temperature dependent. However, 119Sn NMR spectroscopic experiments of {[R(0)Sn]2(CH2)3}m with [R(Cl)2Sn]2(CH2)n for longer spacers (n - 5, 6, 8, 10, 12) reveal that molecular self-assembly of symmetric spacer-bridged di-tin precursors of equal chain length is preferred over asymmetric species. An ether-bridged di-tin tetrachloride [R(Cl)2Sn(CH2)3]2O (R = CH2SiMe3) and its corresponding polymeric oxide {[R(O)Sn(CH2)3]2O}m were synthesised and characterised. Reaction of [R(Cl)2Sn(CH2)3]2O with {[R(O)Sn(CH2)3]2O}m results in a unique functionalised double ladder {{[RSn(Cl)](CH2)3O(CH2)3[RSn(Cl)]}O}4 whose structure in the solid state was determined by X-ray analysis. Identification of tetrameric functionalised double ladder as well as dimeric and monomeric species suggest the existence of an equilibrium in solution. The feasibility of the functionalised double ladder to form host-guest complexes with a variety of metal cations is investigated using electrospray mass spectrometry (ESMS). Evidence for such complexes is found only for sodium cations. The reaction between {[R(O)Sn]2(CH2)n}m (n = 3, 4, 8, 10) and triflic acid is described. The initial formed products [RSn(CH2)nSnR](OTf)4 are easily hydrolysed. For n = 3, self-assembly leads to a discrete double ladder type structure, {{[RSn(OH)](CH2)3[RSn(H2O)]}O}44OTf, which is the first example of a cationic double ladder. For n ≥ 3, hydrolysis gives polymeric products, as demonstrated by the crystal structure of {[(H2O)(OH)RSn]2(CH2)4-2OTf2H2O}m. Two spacer-bridged terra-tin octachlorides [R(Cl)2Sn(CH2)3Sn(Cl)2]2(CH2)n (R = CH2SiMes; n = 1, 8) and their corresponding polymeric oxides {[R(O)Sn(CH2)3Sn(O)]2(CH2)n}m were successfully synthesised and characterised. Attempts were made to synthesise quadruple ladders from these precursors. Reactions of [R(Cl)2Sn(CH2)3Sn(Cl)2]2CH2 with {[R(O)Sn(CH2)3Sn(O)]2CH2}m or (Y-Bu2SnO)3 result in, mostly insoluble, amorphous solids. Reactions of [R(Cl)2Sn(CH2)3Sn(Cl)2]2(CH2)8 with {[R(O)Sn(CH2)3Sn(O)]2(CH2)8}m or (t-Bu2SnO)s result in new tin-containing species which are presumably oligomeric. The synthesis of a series of alkyl-bridged di-tin hexacarboxylates [(RCO2)3Sn]2(CH2)n (n = 3, 4; R = Ph, c-C6H11, CH3, C1CH2) is also reported. The hydrolysis of these compounds is facile and complex. There appears to be no correlation between spacer chain length and hydrolysis product. However, the conjugate acid strength of the carboxylate does appear to be important. In general only insoluble amorphous polymeric organotin-oxo compounds were obtained.

Thesis (Ph. D.)--University of Hong Kong, 1988.

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.

This thesis describes the reductive functionalisation of the uranyl(VI) dication by metalation of the uranyl oxo-groups (O=UVI=O), using reductants from Group I, Group II, Group IV, Group XII and Group XIII as well as from the lanthanide and actinide series of the periodic table. Chapter 1 introduces uranium and nuclear waste, and gives an introduction into uranium(V) chemistry. It further compares the chemistry of uranyl(V) to neptunyl(V), with a specific focus on solid state interactions. The chemistry of the Pacman calixpyrroles is briefly introduced. These macrocyclic ligands form the basis for the synthesis of uranyl Pacman, which represents the major uranyl complex investigated in this thesis. Chapter 2 describes the reductive and catalytic uranyl oxo-group metalation using Group XIII and Group I reagents. It presents the reductive uranyl alumination using di-(iso-butyl)-aluminium hydride and Tebbe’s reagent to form the first Al(III)- uranyl(V) oxo complexes (AlIII-O-UV=O). The chapter shows how the transmetalation of these aluminated uranyl(V) complexes with alkali metal hydrides and alkyls leads to the formation of mono-metalated alkali metal uranyl(V) complexes (MI-O-UV=O). The combination of these two reactions is developed into a catalytic synthesis of the latter. The use of elemental alkali metals is described as another pathway of accessing alkali metal uranyl(V) complexes, carried out in collaboration with Dr. Rianne M. Lord. Chapter 3 describes the synthesis of the first Group IV uranyl(V) complexes, using low-valent titanium and zirconium starting materials. The chapter includes magnetic measurements on the first Ti(III)-uranyl(V) complex and a comparison of computational results regarding a selection of uranyl(V) complexes from this thesis. The magnetic measurements were carried out by Dr. Alessandro Prescimone, University of Edinburgh, and analysed by Dr. Nicola Magnani, Institute for Transuranium Elements, Karlsruhe, Germany. Theoretical calculations were carried out by Xiaobin Zhang and Prof. Dr. Georg Schreckenbach, University of Manitoba, Canada. The chapter further describes the reductive metalation of uranyl using elemental Mg, Ca and Zn and their respective metal halides. Chapter 4 describes the uranyl functionalisation using f-elements and their complexes. It describes the attempted mono-metalation using lanthanides and the formation of a Sm(III)-bis(uranyl(V)) complex. It further describes the uranyl reduction using actinides and the synthesis of the first U(IV)-uranyl(V) complex. The chapter further describes the first Np(IV)-uranyl(V) complex and the attempted synthesis of a Pu(IV)-uranyl(V) complex. These syntheses were performed in collaboration with Michał S. Dutkiewicz at the Institute for Transuranium Elements (ITU) in Karlsruhe, Germany. This work was carried out with the help of Dr. Christos Apostolidis and Dr. Olaf Walter and supervised by Prof. Dr Roberto Caciuffo. Chapter 5 describes the reductive uranyl functionalisation in a redox-active dipyrromethene ligand, collaboratively carried out with James R. Pankhurst and Lucy N. Platts. The synthetic work and analyses were performed jointly with Lucy N. Platts (master student under the supervision of the author); UV-vis spectra and cyclic voltammograms were recorded by James R. Pankhurst and Lucy N. Platts. The chapter presents the synthesis of a new uranyl(VI) complex and its two-electron reduction to uranium(IV) using a titanium(III) reductant. Additionally the chapter describes the reductive uranyl silylation in a dipyrromethane complex of which the ligand was designed by Dr. Daniel Betz. Section 6 describes the synthetic procedures. Section 7 gives references to the work of others. Section 8 shows the publication related to this thesis. Section 9 is a table of the complexes described in this thesis.

>Magister Scientiae - MSc / Herein we report the successful synthesis of a class of stable and flexible Schiff-base chelators capable of coordinating both ruthenium (II) and rhenium (VII) and which would be catalytically active for oxo-transfer reactions. The synthesis of bidentate (L1), tetradentate (L2-L3), and multidendate ligands (DL1-DL4) of nitrogen was a result of a reaction of primary amine with 2-pyridinecarboxaldehyde. Ligand (L3) is reported herein for the first time. The amines (n-propylamine, ethylenediamine, butanediamine, diaminobutane, propylene iminopyridyl (DAB-PPI) dendrimer) were varied as to afford metal complexes that exhibit different physical and chemical properties. The ligands were isolated and fully characterized by IR, NMR spectroscopy and elemental (H, C, N) analysis.The Schiff-base complexes of methyltrioxorhenium (MTO): Methyl(n-pyridin-2-yl)methylene)propan-1-amine)trioxorhenium (C1), Methyl([bis(pyridin-2- yl)formylidene]butane-1,4-diamine)trioxorhenium (C2), Methyl(diaminobutane propylene imonopyridyl)trioxorhenium G1(DC1) and G2(DC2) have exhibited sensitivity to water than MTO itself. Rapid ligand-exchange reactions in solution are observed at elevated temperatures. The MTO Schiff-base complexes are also slightly sensitive to light and slowly decompose as they are exposes to air. These complexes were isolated and fully characterized by IR, NMR, UV-Vis, EA and MS. In the ESI mass spectra of compound C1-C2 and DC1-DC2 show the peaks of the Schiff-base ligand and the MTO moiety separately, without a traceable fragmentation pattern. The isotopic cluster and the molecular ion peak were observed.The mononuclear ruthenium compounds (B1 and B3) were prepared from dichlorotetrakis(dimethyl sulfoxide)ruthenium (II) metal precursor by reacting the synthesized ligands (L2 and L3) with the metal precursor. Compounds (B2 and B4) were obtained by subsequently stabilizing the neutral compounds (B1 and B2) as hexaflourophosphate salts via metathesis employing thallium (I) hexafluorophosphate (V).The homobimetallic cationic compound (B5) was synthesized by reacting the dinuclear complex [(p-cymene)2RuCl2]2 with ligand (L4).The neutral tetranuclear (V1 and V3) and octanuclear (V2 and V4) (N,N) ruthenium(II) metallodendrimers were synthesized mimicking the same route as for the neutral mononuclear compounds (B1 and B3). The compounds (V1-V4) were prepared from the dichlotetrakis(dimethyl sulfoxide)ruthenium(II) based on the synthesized dendritic scaffolds (DL1-DL4). Compounds (V5 and V6) were fashioned in a similar manner to compound (B5),by reacting the iminopyridyl dendritic scaffolds (DL1 and DL3) with the dinuclear precursor[(p-cymene)2RuCl2]2 to afford two complexes of the type [{(p-cymene)RuCl2}4G1, V5] and [{p-cymene)RuCl2}8G2, V6]. Electronic spectra of the prepared complexes were obtained (in a Sharpless Biphasic solvent system: CCl4:MeCN:H2O) in order to understand the nature of the active species in the catalytic cycle and to propose a mechanism for the catalytic cycle .Confirmation of the prepared complexes (B1-V6) was done using several spectroscopic techniques (IR, NMR, UV-Vis, ESI-MS) in conjuction with elemental analysis.The compounds C1-DC2 were then tested towards the epoxidation of selected cyclic alkenesi.e cyclohexene and cis-cyclooctene, respectively and straight chain alkenes. The catalyzed epoxidation reactions were carried out at room temperature employing using Urea hydrogen peroxide adduct (UHP) as the oxidant and dichlomethane (DCM) as the solvent. The complexes displayed high catalytic activity and selectivity when applied to the epoxidation of cyclohexene and cis-cyclooctene with urea hydrogen peroxide adduct (UHP) as oxidant in dicholoromethane. The epoxidation reaction was quantified using gas chromatography.Conversions reached 100% for all the complexes within 6 hours. The catalytic activity of complex C1 and C2 was relatively low compared to the catalytic activity of complex DC1 and DC2.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.