Substituted Derivatives of Tungsten Hexafluoride

Majid, Abdul (1972) Substituted Derivatives of Tungsten Hexafluoride. PhD thesis, University of Glasgow.

Abstract

This thesis describes the perparations of series of derivatives of tungsten (VI) fluorides, and experimental techniques, used to investigate their physical and chemical properties, particularly 19F n.m.r spectroscopy and 18F tracer techniques. The substituents X of the series WF6- nXn which are investigated are -NMe2,-Net2, -OC6F5,-OC(O)R (where R=Me or CF3) , CN,NCO and Cl. They were chosen to develop different aspects of the chemistry of W(Vl), in particular to investigate the effects of ligands of different electronic and steric properties on the reactivities and stereochemistry of the compounds. Dialkyl amino derivatives of tungsten hexafluoride of the type WF6-n (NR2)n (R=Me,n=1 ;R=Et,n=1, 2 and 4) are obtained from the stoichiometric reactions of tungsten hexafluoride with dialkylamino trimethylsilanes. Attempts to prepare WF3(NEt2)3 by this method were unsuccessful and led to the formation of WF4(NEt2)2 or a mixture of unidentified species. The physical properties of WF5NR2 and WF4. (NEt2)2 are consistent with their being associated but WF2(NEt2)4 appears to be monomeric. Substitution of the fluoride by chloride, rather than W-N bond cleavage, occurs in reactions of WF5NEt2 with anhydrous hydrogen chloride. Analyses of the compounds obtained from the reactions of WF5NEt2 with Me3SiCl are consistent with the presence of more than one species, which are not completely characterized. WF5NEt2 reacts with (MeO)2S-O giving WF4(NEt2) (OS(O)OMe] which slowly decomposes to WF4(OMe)(NEt2). The n.m.r spectra of the products from the reactions of WF5MEt2 with trimethylmethoxysilene are consistent with the presence of more than one species. WF(OMe)2(NEt2)3 and WFCl2(NEt2)3 are obtained from the reactions of WF2(NEt2)4 with Me3SiOMe and Me3SiCl respectively. The reactions of tungsten hexafluorido with tris(dimethylamino) phosphine and trimethylsilyl imidazole are also described. Tungsten hexafluoride undergoes aminolysis with diethylamine, which has been followed by conductometric titrations in acetone solution, WF5OC6F5 and MoF5OC6F5 are prepared from the reaction of WF6 with Me3SiOC6F5(1 : 1 mole ratio). The molecular weight determinations and 19F n. m. r spectrum of WF5OC6F5 are consistent with its monomeric nature. The difference in the ortho and para fluorine chemical shifts of pentafluorophenyl group in WF5OC6F5 is smallest among the pentafluorophenyl derivatives, which suggests that -OWF5 is an pi electron acceptor group. The colour of both WF5OC6F5 and MoF5OC6F5 is ascribed to intramolecular charge transfer from the pentafluorophenyl ring to the non bonding orbitals of tungsten. The 19F n.m.r spectrum of the product obtained from the reaction of WF6 (1 mole) with Me3SiOC6F5 (2 moles) is consistent with a mixture including WF5OC6F5 and WF4(OC6F5)2. Carboxylato tungsten (VI) fluorides cannot be isolated from the reactions of WF6 with Me3SiOC(O)R, where R=CH3,CF3,C3F7. Tungsten hexafluoride undergoes substitution reaction with Me3SiX(X= CN or NCO), but the products are not completely charactrized. A fluorine-18 tracer technique has been developed to study the exchange reactions of WF6-nXn (where X=NEt2,0Me,OPh, OC6F5;n=1-4) with Me3SiF. The rate of exchange depends on the nature and number of substituents, concentrations, stoichiometry of the reactants and the reaction conditions. The mechanism of the exchange reactions can be related to the mechanism of substitution reactions.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Inorganic chemistry
• Date of Award: 1972
• Depositing User: Enlighten Team
• Unique ID: glathesis:1972-78599
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:09
• Last Modified: 30 Jan 2020 15:09
• URI: https://theses.gla.ac.uk/id/eprint/78599