published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

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This thesis discusses the investigation of the two-dimensional S = œ Heisenberg antiferromagnet copper formate tetrahydrate (CFTH) and the layered triangular lattice material NaTi0₂ which was thought to be a candidate for the possession of a non-classical antiferromagnetic ground state due to the frustration inherent in a triangular antiferromagnet. Single crystals of CFTH are investigated using elastic, quasielastic and inelastic neutron scattering, electron spin resonance (ESR) spectroscopy and DC magnetometry. Using the appropriate theory, these measurements are used to determine values for the terms in the Hamiltonian which describes the interactions between the Cu²⁺ ions in this material. The Hamiltonian is compared with that of La₂Cu0₄, and the two are determined to be quite similar. There does not appear to be any evidence for a non-classical ground state in either material. This was proposed to exist in La₂Cu0₄ to account for the superconductivity of doped samples. The difficulties in preparing pure NaTi0₂ have been surmounted, and a technique is described for preparing powder samples with very reproducible structural and magnetic properties. The structural properties have been investigated using X-ray and neutron diffraction, the latter at temperatures between 100 K and room temperature. The magnetic properties have been probed using DC magnetometry and ESR spectroscopy. The sample dependence of the structural and magnetic properties of samples prepared in slightly different ways is discussed. The temperature dependence of the magnetic susceptibility and of the structural parameters is explained by comparison with other oxides and chlorides of trivalent Ti and V, many of which show similar behaviour. The magnetic and structural changes which occur between 200 and 250 K are assigned to changes in the Ti-Ti bonding within the layers, which leads to a transition between two metallic states with subtle differences in their band structures.

This thesis describes the application of (arene)Cr(CO)3 methodology to the Stereoselective and enantioselective synthesis of substituted arenes. Chapter one reviews the main methods of preparation and decomplexation of (arene)Cr(CO)₃ complexes and the electronic and steric influences of the Cr(CO)₃ unit on the arene. Chapter two demonstrates that the benzylic oxygen directing effect in complexation reactions operates via a direct oxygen bond to the incoming metal unit. Attachment of bulky ft-acceptor groups, such as t-butyldimethylsilyl, to the benzylic oxygen overrides this directing effect. Chapter three describes the regioselective Cl functionalisation of the cryptopine skeleton. Complexation of dihydrocrytopine gives only a single product, the relative configuration of the product being determined using an X-ray crystal structure analysis. Subsequent alkylation of the O-methyl derivative gives Cl alkylated products. Chapter four describes the regioselective ortho functionalisation of ephedrine and pseudoephedrine derivatives. Treatment of (1S,2R)-(N,O-dimethylpseudoephedrine) Cr(CO)₃ with n-butyllithium leads to exclusive removal of the pro-(R) ortho proton. The observed stereoselectivity arises via</em deprotonation from cyclic bidentate five-membered chelates. Chapter five describes the regioselective C4 and C5 functionalisation of (hydrocotarnine)Cr(CO)₃. Complexation of 1-methylhydrocotarnine occurs to give exclusively the exo-1-methyl derivative. Further functionalisation to give the 1,5- and 4,5-dimethyl products is also described. Chapter six describes the synthesis of ortho substituted (benzaldehyde)Cr(CO)₃ complexes. Chiral material is available via preferential kinetic hydrolysis of, or classical separation of, the L-valinol derived imines. Chapter seven describes the Stereoselective addition of nucleophiles to (o-anisaldehyde) Cr(CO)₃ and (o-trialkylsilylbenzaldehyde)Cr(CO)3. With (o-anisaldehyde)- Cr(CO)₃ the additions are completely stereoselective giving the (RR,SS) diastereoisomer. With (o-trialkylsilylbenzaldehyde)Cr(CO)₃ the ratio of products is influenced by the nature of Lewis acidic species present. Chapter eight describes the Stereoselective benzylic elaboration of (o-methoxybenzyl methyl ether)Cr(CO)₃ achieved via selective removal of the exo benzylic proton from transition states with the methoxy groups anti to each other.

This thesis deals with the applications of organopalladium and organochromium chemistry to the functionalisation of the benzopyran ring system, at a variety of oxidation levels. Section I demonstrates the functionalisation of 3-, 6-, and 8-bromochromones via palladium (0) insertion into the C-Br bond. The resultant arylpalladium species are shown to undergo addition to the least substituted end of a variety of olefins including methyl acrylate, acrylonitrile and styrene. Subsequent palladium-hydride elimination leads to overall palladium catalysed vinylation of the chromone and the synthesis of a number of novel compounds. Vinylation occurs regiospecifically at the site of chromone bromination and is shown to allow clean substituent introduction into each of the three sites. The palladium catalysed reaction of 3,6-dibromo-chromone with methyl acrylate leads to vinylation at both the C3 and C6 positions. Carbonylation of the 6-bromochromone in ethanol or butanol leads to the 6-ethyl or 6-butyl esters respectively. The palladium catalysed vinylation of the 6-bromochromone with ethyl vinyl ether leads to a mixture of products from addition of the chromone to either end of the olefin. With p-bromophenol or p-bromo-N,N-dimethylaniline the reaction gives exclusively the acetylated product arising from addition to the more substituted end of the olefin. This change in orientation is rationalised by considering the polarisation of the olefin and the arylpalladium species. Section II demonstrates the functionalisation of chroman and 4-chromanol via coordination to the Cr(CO)₃ moiety. (η⁶-Chroman)Cr(CO)₃ is synthesised and is shown to undergo regiospecific ring deprotonation at C8 under kinetic conditions or regiospecific benzylic deprotonation at C4 under thermodynamic conditions. The resultant anions are quenched with alkyl halides, aldehydes, Eschenmoser's salt and methyl disulphide resulting in selective functionalisation of either site. No mixed products are observed. The uncomplexed arene is shown to be totally unreactive under identical conditions. (η⁶-4-Chromanol)Cr(CO)₃ is synthesised and is shown to undergo regiospecific C8 ring deprotonation by comparison with authentic samples of the C5 and C8 methylated alcohols. Protection of the hydroxyl group as its methyl, t-butyldimethylsilyl or methoxymethyl ethers is found not to alter the regiochemistry of deprotonation. The 4-chromanol t-butyldimethylsilyl and tri-i-propylsilyl ethers are synthesised and coordinated to the metal unit. Cleavage of the silyl ethers is shown to proceed with loss of stereochemistry, indicating C-0 bond cleavage.

This Thesis describes the synthesis, structural characterization and properties of some tin(II) and tin(IV) compounds containing bidentate ligands. Chapter 1 describes the main spectroscopic techniques used in the identification of tin(II) compounds; infra-red, ¹¹⁹Sn Mössbauer and n.m.r spectroscopy are outlined, and relevant examples given. A comprehensive listing is given of the main spectroscopic and structural properties of known tin(]3) compounds. Chapter 2 describes the general synthetic methods employed for the formation of tin(II)-oxygen heterocyclic compounds. A range of catecholate and related complexes of tin(II) were synthesized and the role of the substituent investigated with regard to their physical properties, especially their solubilities. The use of 4-nitrocatechol leads to a soluble product, {Sn[O-4-NO₂-C₆H₃O][OC₄H₈]}>sub>n</sub>, which enabled it to be studied spectroscopically and its solid state structure to be determined. The nature of the bonding in {Sn[O-4-NO₂-C₆H₃O][OC₄H₈]}_n was investigated using Extended Hiickel molecular orbital calculations. Chapter 3 describes the chemical reactivity of the novel, soluble, tin(II)-oxygen heterocycle {Sn[O-4-NO₂-C₆H₃O][OC₄H₈]}_n. Reaction with iodine gives SnI₂ [O-4-NO₂-C₆H₃O][OC₄H₈]<sub>2<sub>. Reaction with the Lewis base such as 1,2-diaminopropane gives Sn[NH₂CH₂CH(Me)H₂N][O-4-NO₂-C₆H₃O][OC₄H₈], whilst benzyltriethylammonium chloride gives {[Et₃BzN][SnCl(O-4-NO₂-C₆H₃O)]}_n. The solid-state structure of the compound consists of polymeric chains of [SnCl(O-4-NO₂-C₆H₃O)]^- and associated [Et₃BzN]⁺ cations. Reaction with BF₃.Et₂O gives the adduct F₃B.Sn[O-4-NO₂- C₆H₃O][OC₄H₈]. Reaction with W(CO)<sub>5_{thf gives {(OC)₃W.Sn[(O-4-NO₂- C₆H₃O)(OC₄H₈)]}₂ in which the tungsten atoms are believed to be bound η⁶ to the aromatic rings. Reaction with bis(triphenylphosphine)platinum-ethylene or tris(triphenylphosphine)platinum gives {PtH[PPh₃]₃}{[μ₂-O][μ₂-OH][Sn(O-4-NO₂- C₆H₃O)]₂}, the anion containing tin(II) and tin(IV) centres. Reaction with RhCl[CNC₈H₉]₃ gives {RhCl[CNC₈H₉]₃[μ₂-Sn(O-4-NO₂-C₆H₃O)]}₂. Reaction with Ph₃PAuCl gives the cluster Au₄(PPh₃)₄(μ₂-SnCl₃)₂, which is the first known example of a compound containing a μ₂-SnX₃ fragment. In comparison with SnCl₂, {Sn[O-4-NO₂- C₆H₃O][OC₄H₈]}_n only weakly inserts into the platinum-chlorine bonds of PtCl₂(dppe). Two molar equivalents of SnCl₂ reacts with PtCl₂(dppe) to give Pt(dppe)(SnCl₃)₂. Addition of a further equivalent of SnCl₂ in the presence of tetraethylammonium chloride gives [Et₄N][Pt(dppe)(SnCl₃)₃]. The platinum centre in this ion has a distorted trigonal bipyramidal geometry. Chapter 4 describes the synthesis of a number of tin(II)-sulphur heterocycles. The reaction between Sn[SC₆H₄S] and TMEDA gives a soluble adduct, Sn[SC₆H₄S]TMEDA. A number of tin(II)-nitogen heterocycles were also synthesized. Their intense colours and their instability towards air oxidation indicated that they were monomeric in the solid-state. Chapter 5 outlines the basis for non-linear optical properties, especially their SHG effects. A wide range of tris(catecholato)tin(IV) compounds were synthesized and tested for SHG activity. A number were found to have a significant SHG effect, especially [(O-4- NO,sub>2}-C₆H₃O)₃Sn][NHEt₃]₂, which has an SHG effect 1.33 x urea.

Offprints of two author's journal articles inserted at end of the v. / Bibliography: leaves 10-12 / 216 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1985

Typescript (photocopy) / viii, 283 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1980