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Title: New routes to fluorocarbon-containing phosphines
Author: Herbert, Christopher James
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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Routes to sterically demanding organofluorine-containing phosphines are described, and the stereoelectronic properties and chemistry of the resulting new ligands investigated. The synthesis of Cy2P(CF=CF2), 3, has been accomplished. The nucleophilic substitution of Ph2P(CF=CF2) with tBuLi produces the (Z)-isomer, Ph2P(Z-CF=CF(tBu)), 5-(Z), predominantly, which has been shown to be less electron-withdrawing than Ph2P(CF=CF2), and similar in size to 3. The bis-trifluoropropynyl substituted phosphine PhP(tfp)2, 7, has been prepared, and its reaction with tBuLi investigated. This results in the formation of three previously unknown species, the gem¬-difluorocyclopropenyl-containing compound, PhtBuP(dfcp), 8, (Z)-Ph2P(CH=C(t¬Bu)CF3), 9, and PhtBuP(tfp), 10. The nucleophilic substitution occurs preferentially at the phosphorus centre, as shown by the reaction with one equivalent of tBuLi at -60°C, where compounds 9 and 10 are formed. A new route to perfluoroalkyl-containing phosphines has been discovered. The addition of a perfluoroalkyl iodide to Ph2PSiMe3 results in the formation of six new phosphines, and has been shown to be extendable to partially fluorinated systems. The route can also be applied to iPr2PSiMe3, and to the chiral phosphine PhMePSiMe3. Three examples, Ph2PRf (Rf = CF(CF3)2, 15, (sC4F¬9), 18, (cyc-C6F11), 19), have been produced on a preparative scale. The reaction of the bis-trimethylsilyl phenyl phosphine with (CF3)2CFI has been investigated, though it does not result in the production of the bis-perfluoroalkyl-substituted phosphine, instead the previously unknown P-chiral compound, PhP(H)CF(CF3)2, 27 is formed. Mechanistic studies have indicated that Ph2P-PPh2 is the intermediate, and that there is no evidence of a radical mechanism. There is no reaction between Me2(S)P-P(S)Me2 and (CF3)2CFI, though there is when Me2P-P(S)Me2 is used, suggesting that the lone pair of the intermediate diphosphine is necessary for the reaction to proceed. This has resulted in the formation of the new compound, Me2PCF(CF3)2, 28. The chemistry of the perfluoroalkyl-containing phosphines has been investigated; they do not quaternise, but are oxidatively sensitive. The phosphorus(V) selenides of 15, 18, and 19 have been prepared, and based on their 1JPSe coupling constants, the perfluoroalkyl-groups impart a greater electron-withdrawing effect than perfluorovinyl, trifluoropropynyl, or alkoxy fragments. The oxidation of 15 and 18 with XeF2 has also been accomplished, and shown to yield the corresponding F2PPh2Rf compounds. The molybdenum(0) pentacarbonyl complexes of 3, 7, and 15 have been synthesised and perfluoroalkyl-groups have again been shown to be more electron-withdrawing than perfluorovinyl and trifluoropropynyl groups by comparison of v(CO) values. The gold(I) chloride complexes of Ph2PCF3, 15, and 18 and the platinum(II) dichloride complexes of 3 and 15 have been prepared, and the size of these ligands has been estimated from the crystal structures. Compound 18 has been shown to be the largest of these compounds, with a cone angle of 187°.
Supervisor: Brisdon, Alan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: fluoroalkyl ; fluorocarbon ; phosphine ; fluorine ; electron-withdrawing