The Preparation and Properties of Tungsten Hexafluoride Derivatives

Noble, Alexander MacIver (1970) The Preparation and Properties of Tungsten Hexafluoride Derivatives. PhD thesis, University of Glasgow.

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The original aim of this investigation of the virtually unexplored chemistry of tungsten hexafluoride, WF6, was to assess its usefulness as a fluorinating agent towards organic compounds. It is shown that WF6 is a mild,selective fluorinating agent, limited in its applications. The work includes a study of the properties of derivatives of WF6, and 19F nuclear magnetic resonance spectroscopy has been used extensively. A Raman spectroscopic study of the coloured solutions of in the donor solvents benzene and acetonitrile indicates that the octahedral symmetry of WF6 is preserved and that the extent of donor-acceptor interaction is small. Nitromethane was found to be a convenient solvent for the preparation of the complex fluorides R4N+WF6- (R = nBu, nPr) by reaction of with the appropriate tetraalkyl ammonium iodide. Attempts to isolate a solid donor-acceptor complex of with a polycyclic aromatic hydrocarbon were unsuccessful Oxotetrafluoro(dimethyl ether)tungsten(VI), WOF4. OMe2 , was obtained in good yield from the reaction of with dimethyl ether under forcing conditions, and it is formulated as a monomeric, octahedral complex on the basis of its spectroscopic properties. The analogous complex WOF4. OEt2 decomposes readily. The interaction of WF6 with thioethers and selenoethers has been studied, and the complexes WF6(Et2S)2 and WF6(Et2Se)2 have been characterised. 19F n. m. r. evidence has been obtained for the formation of the dimeric fluorine-bridged anion W2O2F9 - as hydrolysis product of WF6 derivatives. The fluorination of some oxygen-containing compounds of sulphur and phosphorus by WF6 has been studied. The reaction of WF2 with dimethyl sulphoxide is complicated by the formation of HF, and one of the products is formulated as bis(monofluoromethyl)ether. WF6 undergoes substituent-exchange reactions with sulphite esters to yield alkoxy and phenoxy tungsten(VI) pentafluorides, WF5 or, (R=Me,Et,Ph) and fluorosulphite esters, ROS(O)F. The properties of these products are described. Pyrosulphuryl fluoride, S2O5F2 , is formed in the reaction of WF6 with sulphur trioxide. The reaction of WF6 with trimethyl phosphite gives initially WF5 OMe and PF(OMe)2 , but subsequent reactions occur to give (MeO)2P(O)Me, MeP(O)(F)OMe, (MeO)3PMe+WOF5- and WOF4. OP(OMe)2Me. The products obtained depend on the reaction conditions. PF3 is formed in the reaction of WF6 with dimethyl phosphite, and WF5OMe, WOF4. OP(OMe)2Me and MeP(O)(F)OMe are the products of the reaction of WF6 with (MeO)2P(O)Me. The reactions of WF5OMe with dimethyl sulphite, trimethyl phosphite, benzene, pyridine and dialkyl ethers are described. The fluorination of methylalkoxysilanes and trimethylphenoxysilane with WF6 has yielded a series of methoxy and phenoxy tungsten(VI) fluorides, WF6-n(OR)n, n = 1-4 (Me) n = 1, 2 (Ph), and some evidence for the formation of WF4(0Et)2 and WF3(OPh)3 has been obtained. 19F n. m. r. spectra indicate that these compounds are monomeric in solution, and geometrical isomers have been distinguished in some 19 cases. The 19 F resonances are all to high field of WF6, and the effects of OMe and OPh substituents on the chemical shifts are approximately additive. WF4(OMe)2 isomerises to WOF4.OMe2, and thermal decompositions of methoxy tungsten(VI) fluorides yield Me2O or MeF with some reduction of the tungsten. WOF4 is formed in low yield in the reaction of WF6 with hexamethyldisiloxane; the other products are Me3SiF and reduced tungsten species. Cleavage of the Si-N bond in dimethylaminotrimethylsilane with WF6 was observed, but dimethylamino derivatives of WF6 were not isolated. Some of the factors which may determine the 19F chemical shifts and stereochemistry of the tungsten fluoro-complexes prepared in this work are discussed. The 183W chemical shifts of some of the complexes have been obtained by heteronuclear magnetic double resonance techniques, and these are all to low field of WF6.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Inorganic chemistry, Physical chemistry
Date of Award: 1970
Depositing User: Enlighten Team
Unique ID: glathesis:1970-78530
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:12
Last Modified: 30 Jan 2020 15:12

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