Nucleophilic substitution reactions involving phosphate monoesters have been investigated. Two general syntheses of O-alkyl or O-aryl [16O,18O] thiophosphate monoesters are reported. An independent and general method for the determination of the enantiomeric excess of isotopically chiral thiophosphate monoesters has been developed and the absolute configurations of the diastereoisomers of (2R)-O-(O-ethyl thiophosphoryl)-3, 4S-dimethyl-5S-phenyl-l,3,2-oxazaphos- pholidin-2-one have been assigned. The solvolysis of p-nitrophenyl [R-16O,18O] thiophosphate in ethanol gives rise to ethyl [16O, 18O] thiophosphate with a large degree of racemisation of configuration (~80%). This observation is consistent with the formation of a thiometaphosphate intermediate of finite life-time which is then trapped by ethanol with accompanying loss of stereochemical integrity. This study provides the first direct evidence for a monomeric thiometaphosphate in protic solvent. During the course of developing the stereochemical analysis, it was noted that O-ethyl thiophosphate reacts with cis-2-chloro-3, 4-dimethyl- 5-phenyl-l, 3, 2-oxazaphospholidin-2-one with ca. 10% inversion and 90% retention of configuration. This system also reacts with fluoride ion with complete loss of stereochemistry. Cis-2-chloro-3, 4-dimethyl-5- phenyl-l, 3, 2-oxazaphospholidin-2-one and the corresponding 2-thione are epimerised to the more stable trans isomers by pyridine and other nucleophilic catalysts. These reactions require an in-line exocyclic displacement at a phosphorus centre held in a five-membered ring. Nucleophilic substitution at di- and tri-esters have also been studied. The stereochemical course of the hydrolysis of the 1, 3, 2-dioxaphosphor- inan-2-one system involving good leaving groups such as chloride and fluoride occur with inversion of configuration via an in-line mechanism, whereas hydrolysis of this system involving poor leaving groups occurs with retention of configuration via a pseudorotation mechanism.

This thesis deals with the palladium-catalyzed nucleophilic substitution of π-activated alcohols in which the C–O bond of a non-manipulated hydroxyl group is cleaved. The thesis is divided in two chapters describing two different catalytic systems. Chapter 2 describes a heterogeneous palladium-catalyzed transfer hydrogenolysis of primary, secondary, and tertiary benzylic alcohols to generate the corresponding aromatic hydrocarbons using formic acid as the hydrogen donor. A detailed mechanistic investigation of this reaction has been conducted that establish the kinetic order of each reaction component and also the deuterium kinetic isotope effects. This data provide a mechanistic picture that the hydride transfer from formic acid to palladium, and not the C–O bond cleavage, is involved in the rate-determining step and that a catalytic amount of a base promotes the transfer hydrogenolysis. Chapter 3 describes the development, mechanistic studies and synthetic scope of a homogeneous palladium-catalyzed amination of allylic alcohols. Isolation of the catalyst precursor and equilibrium studies of the palladium and π-acidic triphenylphosphite ligand show unique properties of this catalytic system. Stereochemical, kinetic, and kinetic isotope studies have been performed to provide insight into the mechanism of C–O bond cleavage of allylic alcohol and C–N bond formation catalyzed by the palladium complex. Interestingly, both O–H and C–O bond cleavages are involved in rate-determining steps.

No description available.

<p> Arenechromiumtricarbonyl complexes have been known for many years and numerous studies of the chemistry of these molecules have been reported. The presence of the chromiumtricarbonyl unit changes the reactivity of the complexed arena, in most cases due to its strong inductive electron withdrawing effect. The resulting lowered electron density in the aromatic ring allows reactions to be carried out which would otherwise be extremely difficult if not impossible, notably nucleophilic substitution. When methoxide ion was reacted with optically pure methyl o-fluorobenzoatechromiumtricarconyl, racemization of approximately 50% was observed in the product. A brief study confirmed SN2 kinetics, but further investigation was warranted. Having eliminated the possibility of decomplexationrecornplexation, two other mechanisms were postulated -a partial decomplexation allowing the arene to roll over, or attack by methoxide at another ring position. In an effort to determine which mechanism was operating, the synthesis of a number of appropriately substituted halo-arenechromiumtricarbonyl complexes was attempted. The successful synthesis of methyl 2-chloro-5-methylbenzoatechromiumtricarbonyl wns achieved, albeit with some difficulty in in low yield, but the corresponding 2-chloro-3-methyl complex could not be made. In the case of the corresponding 2-fluoro compounds, the arenes themselves could not be made by a variety of synthetic routes, 80 synthesis of the complexes could not be attempted. The results of the reaction of methoxide ion with methyl 2-chloro-5-methylbenzoatechromiumtricarbonyl indicate that the reaction proceeds via the roll-over mechanism, although a definite conclusion cant be drawn at this time. A potentially useful synthesis of bis-(chromiumtricarbonyl)-benzo-phenones has also been developed. </p> / Thesis / Master of Science (MSc)

No description available.

Diels-Alder polyphenylenes (DAPPs) are chemically and thermally stable polymers, used for dielectric resins, gas separation membranes, and fuel cell proton exchange membranes. Highly fluorinated DAPPs are expected to have better thermal stability and chemical resistance, higher glass transition temperatures, improved compatibility with other fluorinated polymers (like NafionTM), and better adhesion to certain surfaces such as some metals. This thesis proposes a synthesis of highly fluorinated DAPPs by reacting novel, fluorinated bis-cyclopentadienone (CPD) monomers with known aromatic dialkynes. This thesis starts with an introduction to DAPP synthesis, properties, and applications. The second chapter focuses on the synthesis of 4,4′-bis[1,2,4-tris(perfluoro-4-tolyl)cyclopentadien-5-one-3-yl]octafluorobiphenyl (CPD monomer). In the first step, disodiumbis(cyclopentadieny)octafluorobiphenyl was combined with 6 equivalents of octafluorotoluene in HMPA to give 4,4′-bis[1,2,4-tris(perfluoro-4-tolyl)cyclopentadiene-3-yl]octafluorobiphenyl. Oxidation to the corresponding diketone was effected using selenium dioxide. The synthesis of CPD monomer presented several unexpected challenges that were ultimately overcome. The third chapter describes a series of initial polymerization experiments as well as some model reactions that were carried out to understand monomer reactivity. Finally the future research plan of synthesizing different polymers by Diels-Alder reaction and nucleophilic substitution reaction has been discussed. / Master of Science

The second order rate constants for nucleophilic substitution by methoxide of (Z)- and (E)-O-methylbenzohydroximoyl fluorides [C6H4C(F)=NOCH3] with various substituents on the phenyl ring [p-OCH3 (1h, 2h), p-CH3 (1g, 2g), p-Cl (1f, 2f), p-H (1e, 2e), (3,5)-bis-CF3 (1i, 2i)] in 90:10 DMSO:MeOH have been measured. A Hammett plot of these rate constants vs σ values gave positive ρ values of 2.95 (Z isomer) and 3.29 (E isomer). Comparison of these rates with methoxide substitution rates for Omethylbenzohydroximoyl bromide [C6H4C(Br)=NOCH3] and Omethylbenzohydroximoyl chloride [C6H4C(Cl)=NOCH3] reveal an element effect for the Z isomers of Br:Cl:F(1e) = 2.21:1.00:79.7 and for the E isomers of Cl:F(2e) = 1.00:18.3. With the p-OCH3-imidoyl halides the following element effects are found: Br:Cl:F(1h) = 2.78:1.00:73.1 for the Z isomer and Br:Cl:F(2h) = 1.97:1.00:12.1 for the E isomer. Measurement of activation parameters revealed ∆S≠ = -17 eu for 1e and ∆S≠ = -9.9 eu for 2e. Ab initio calculations (HF/6-31+G*, MP2/6-31+G*//HF/6-31+G*, B3LYP/6- 31+G*//HF/6-31+G*, HF-SCIPCM/6-31+G*//HF/6-31+G*) were performed to define the reaction surface. These calculations demonstrate a relatively large barrier for nucleophilic attack in relation to halogen loss and support the experimental findings that this reaction proceeds by an addition-elimination mechanism (AN# + DN). The imidoyl fluorides have been used to synthesize highly functionalized O-methyloximes by reaction with enolate anions derived from malononitrile, ethyl cyanoacetate, and diethyl malonate. Acid-catalyzed isomerization of compounds containing the O-methyloxime moiety have been investigated with ab initio calculations (HF/6-31+G*, MP2/6- 31+G*//HF/6-31+G*, B3LYP/6-31+G*//HF/6-31+G*). Barriers for rotation around the C-N bond following protonation have been calculated. The calculated barriers are discussed in relation to an isomerization mechanism of protonation-rotation versus a nucleophilic catalysis.

No description available.

Halogenated monocyclic and bicyclic heteroaromatic azines, possessing a six or ten w-electron system and one or two ring nitrogens, have been shown to undergo nucleophilic displacement of halide ion with a variety of nucleophiles. A detailed review of the relative reactivity of compounds of these classes, as well as halogenated heteroaromatic azines containing as many as four nitrogen atoms has appeared. / Ph. D.

The first chapter of this dissertation reports the synthesis of highly fluorinated Diels-Alder polyphenylenes. The first section of this chapter describes the three-pot synthesis of a perfluoroarylated bis(cyclopentadienone) monomer. The synthesis begins with the previously reported substitution reaction of decafluorobiphenyl and sodium cyclopentadienide. To the resulting 4,4'-octafluorobiphenylene-linked bis(cyclopentadiene), six perfluoro-4-tolyl groups (three on each of the two cyclopentadienyl moieties) are attached by nucleophilic aromatic substitution (SNAr) reactions. The remaining ring methylenes are subjected to a selenium dioxide-catalyzed oxidation to obtain the desired bis(cyclopentadienone) monomer. The next part of this chapter describes the polymerization of the perfluoroarylated bis-(cyclopentadienone) monomer and bis(4-ethynylphenyl) ether. The reaction affords an oligomer (Mn ~ 14,000 g/mol according to size-exclusion chromatographic analysis) that is soluble in several solvents and that decomposes above about 300°C according to thermogravimetric analysis. The second chapter of this dissertation describes a novel method to oxidize per-fluoroarylated cyclopentadiene compounds to the corresponding ketones using catalytic selenium dioxide and stoichiometric hydrogen peroxide. The first part of this chapter shows the synthesis of some perfluoroarylated cyclopentadiene substrates, while the second part of the chapter explores the oxidation of these compounds along with other perfluoroarylated cyclopentadienes already available within our research group. This chapter also explains how the reactivity of the perfluoroarylated cyclopentadienes under the oxidation conditions depends on their structure. Generally more electron-deficient cyclopentadienes react more readily, while sterically crowded cyclopentadienes react more reluctantly. This third chapter of this dissertation describes the synthesis and characterization of a reversible Diels-Alder polymer from an octafluorobiphenylene-linked bis(cyclopentadiene). In the first section, the synthesis of a reversible homopolymer of the bis(cyclopentadiene) monomer is described. The polymer reaches an optimized molecular weight of 11,000 g/mol (degree of polymerization is 20) under the reaction conditions because there is an equilibrium between polymerization and depolymerization even at the mild polymerization temperature (65°C). The TGA trace of the polymer shows that chain degradation takes place beyond 300°C. The thermal reversibility of the polymer was examined by bulk thermolysis, and flash-vacuum thermolysis. The second section describes the synthesis of a methylated bis(cyclopentadiene) that does not undergo self-polymerization at comparatively lower temperature but instead reacts with a second bis(maleimide) monomer. The resulting polymer typically shows a number-average molecular weight of 15,400 g/mol. This polymerization also is limited by the attainment of steady-state end group concentrations. The reversibility of the polymerization is demonstrated by solution thermolysis experiments in which unmasked cyclopentadiene groups are trapped by a monofunctional maleimide. / Ph. D.