Ph.D. / The main objective of the research described in this dissertation was the preparation and characterisation of hindered organophosphorus compounds. For this purpose, ionic and free radical mechanisms were applied in the synthesis of selected hindered organophosphorus compounds, some with interesting spectral properties. A brief background of the element phosphorus and the early development of organophosphorus chemistry is provided. The early development of the chemical nerve agents derived from phosphorus, their toxicity and illicit manufacture by terrorist groups is discussed. The vital role played by the organisation for the prohibition of chemical weapons in enforcing the prohibition of the development, production, acquisition, stockpiling and the use of chemical nerve agents and their destruction by the state party is highlighted. The methodologies such as Michaelis Arbuzov, Michaelis Becker, Perkow Pudovik, Abramov and radical protocol reactions used to synthesise phosphorus containing compounds, are reviewed. In the present research project, diphenylphosphonous chloride and phenylphosphonous dichloride reagents were used in nucleophilic substitution reactions with bulky alcohols. This resulted in the synthesis and characterisation by 1H, 13C, 31P NMR and GCMS spectroscopy of the compounds shown in Scheme 0.1, where R’ was derived from 2,2dimethylpropanol, 3methylbutanol, 1,2dimethylpropanol, 3,3dimethyl2butanol, 1,1dimethylethanol and 2methyl2butanol. (R)xPCl(3x) R'OH Et3N (R)xP(OR')(3x) H2O2 or S8 (R)xP(OR)(3x) Y R=Aryl, and Y=O, S The importance of using activated alcohols in the form of metal alkoxides in the cases of 1,1dimethylethanol and 2methyl2butanol for successful reactions was demonstrated. The influence of steric hindrance on the reactivity of these ionic reactions was studied by substituting diphenylphosphonous chloride, or phenylphosphosphonous dichloride, with tertbutylphosphonous dichloride or ditertbutylphosphonous chloride. This resulted in no nucleophilic substitution reaction taking place between tertbutylphosphonous dichloride and hindered alcohols in the presence of triethylamine. For successful reactions, the use of excess activated hindered alcohols in the form of either the lithium or potassium alkoxide was required. It was found that replacing both of the chlorine atoms in tertbutylphosphonous dichloride with hindered alcohols like 1,1dimethylethanol and 2methyl2butanol was sluggish, and in the present study this could not be realised. It was demonstrated that ditert butylphosphonous chloride is resistant to react with activated hindered alcohols due to enhanced steric hindrance in the organophosphorus reagent. The use of freeradical mechanisms in the phosphoruscarbon (PC) bond forming reaction is briefly reviewed. The importance of finding a nontoxic replacement of organotin reagents in radical protocols is also highlighted. The scope of the present work was limited to the reaction of phosphonylcentered radicals generated by the triethylboraneoxygen system with various alkenes ranging from less electron rich to more electron rich alkenes, including those containing a free hydroxy moiety. The reaction of diphenyl thiophosphite or diphenyl phosphite (Scheme 0.2) in the presence of triethylborane under aerobic conditions with enol ether alkenes afforded the expected antiMarkovnikov products.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

A radioisotope of rubidium, 82Rb is used in positron emission tomography. Neutral crown ethers and cryptands have been studied as carrier ligands for Rb+ but exhibit low ion carrying capacity and high toxicity. The present study involved investigating a lariat ether containing an ionizable phosphoryl moiety and a lipophilic sidearm. This kind of molecule is expected to be ionized at physiological pH. It should be able to form neutral complexes with Rb+ and may be able to cross the blood-brain barrier. Molecular modeling of crown ether-alkali metal cation complexes indicates that a macrocycle containing more than 18 but less than 21 atoms can incorporate Rb+ ion in its cavity. Molecular modeling of some of the complexes of phospho-lariat ethers with rubidium using the Spartan'02 software package revealed that a lariat ether containing 20 member macrocycle will probably form the most stable complex with Rb+ion. Also, it was thought that more flexibility could be imparted to the macrocycle if it contains propyleneoxy units instead of ethyleneoxy units which form most crown ethers. Molecular modeling of two phospho-lariat ethers with 16 and 20 membered rings revealed that 20 membered macrocycle may be a better choice due to the side arm's participation in the complexation with Rb+ to a greater extent. Molecular modeling was used to find the bond angles and bond distances in this molecule. The synthesis to obtain ionizable phospho-bipodands was performed using subsequent benzylation, phosphorylation and hydrogenation steps. The characterization of products was done using HPLC, NMR and ESI-MS techniques. The synthetic scheme used was demonstrated to be plausible and could be used to obtain ionizable phoshobipodands. Extraction using solid phase anion exchange columns proved to be a good clean up procedure for obtaining pure bipodand. This bipodand could be used as a precursor for synthesizing an ionizable 20 membered lariat ether.

The clean reaction of 5-lithio-6-diisopropylphosphinoacenaphthene (1') with dichlorophosphines, RPCl₂ (R = Ph, Fc, NMe₂, iPr), led to the formation of peri-substituted phosphino-phosphonium chloride salts 2-5. The synthetic utility of these salts was demonstrated in a range of reactions. Mixed tertiary/secondary bis(phosphines) (6 and 7) were prepared by the LiAlH₄ reduction of phenyl or ferrocenyl phosphino-phosphoniums (2 and 3), and the bis(borane) adduct of 6 was prepared by reduction of 2 with BH₃•SMe₂. Reaction of 2 and 3 with a large excess of MeOTf at elevated temperature gave 1,2-diphosphoniums (11 and 12), which were subjected to reduction and co-ordination to a molybdenum(0) centre. An investigation into the co-ordination chemistry of 2 revealed three distinct modes of reactivity. In the reaction with [(nor)Mo(CO)₄] the Mo(0) complex [(2)Mo(CO)₄Cl] (18) was isolated, in which monodentate co-ordination was observed. [PtCl₂(cod)] reacts with the chloride and triflate salts of 2 to form [(2Cl)PtCl₂] (19) and [((2Cl)PtCl)₂][TfO]₂ (21) respectively, both of which show co-ordination of 2 as a bidentate phosphine/chlorophosphine ligand. A palladium(II) dimer (22) in which 2 forms a chelating phosphine/phosphide ligand was isolated from the oxidative addition of 2 to a palladium(0) complex. The geminally bis(peri-substituted) tridentate phosphine (27) was prepared by reaction of 1' with half an equivalent of iPrPCl₂. 27 has a rather strained geometry, and displays restricted dynamics on an NMR timescale, which leads to anisochronicity of all three phosphorus nuclei at low temperatures. Strained bis and tris(sulfides) 28 and 29 and the bis(selenide) 30 have been isolated from the reaction of 27 with sulfur and selenium, respectively. A series of co-ordination complexes, [(27)Cu(MeCN)][BF₄] (32), [(27)PtCl][Cl] (33), [(27)FeCl₂] (34) and fac-[(27)Mo(CO)₃] (35), with tetrahedral, square planar, trigonal bipyramidal and octahedral geometries, respectively, were synthesised. In all of these complexes the tris(phosphine) backbone is distorted, but to a significantly smaller extent that in the chalcogenides 28-30.

Triaryl phosphates were synthesized from white phosphorus and phenols in aerobic conditions and in the presence of iron catalysts and iodine. Full conversion to phosphates was achieved without the use of chlorine or chlorinated solvents, and the reactions do not produce acid waste. Triphenyl phosphate, tritolyl phosphate and tris(2,4-di-tert-butyl)phenyl phosphate were synthesized by this method with 100% conversion from P₄. Various iron(III) diketonates were used to catalyse the conversion. Mechanistic studies showed the reaction to proceed via the formation of phosphorus triiodide (PI₃), then diphenyl phosphoroiodidate (O=PI(OPh)₂) before the final formation of triphenyl phosphate (O=P(OPh)₃). The nucleophilic substitution of O=PI(OPh)₂ with phenol to form O=P(OPh)₃ was found to be the rate determining step. It was found that by modifying the reaction conditions the same catalytic systems could be used to synthesize triphenyl phosphite directly from P₄. Triphenyl phosphite was synthesized in selectivities of up to 60 %. The mechanism of these transformations was also elucidated. Independent syntheses of the intermediate in the reaction mechanism, O=P(OPh)₂I and its hydrolysis products diphenyl phosphate (O=P(OPh)₂OH) and tetraphenyl pyrophosphate ((O)P(OPh)₂-O-P(O)(OPh)₂) were developed from PI₃. The 2,4-di-tert-butyl phenol analogues of these compounds were also prepared. Bis-(2,4-di-tert-butylphenyl) phosphoroiodidate was then reacted with various alcohols to produce a series of mixed triorgano phosphates.

No description available.