Investigations into the Chemistry of highly fluorinated phosphorus alkoxides

This thesis covers the diverse chemistry of fluorinated phosphorus alkoxides, which display Lewis basic, Lewis acidic, weakly coordinating anion or cation chemistry, depending on thenumber of substituents at the phosphorus centre. The chemistry of highly fluorinated phosphorus (III) alkoxides with the general formula PR3-n(ORF)n {R = Ph; ORF = C(CF3)3, CH(CF3)2; n = 1 to 3} has been re-explored after initial work in the area from the late 1970s.1,2 These are found to be useful as ligands with the combined properties of being both electron-poor and sterically bulky, an area in ligand space that to date is sparsely filled. In order to assess the steric properties of the ligands, Tolman “ligand cone angles” (θ) have been calculated for [Ni(CO)3L] and [W(CO)5L] complexes of each ligand from DFT optimised structures at the (RI-)BP86/SV(P) level and for [Ru(η5-C5H5)(NCMe)2-nL1+n]+[PF6]- (n = 0, 1) and [RhCl(CO)L2] complexes from single-crystal X-ray diffraction data. The first structural characterisation of a metal complex with the tris(perfluoro-t-butyl)phosphite, [Ru(η5-C5H5)(NCMe)2P{OC(CF3)3}3]+[PF6]- (θ = 195 ) is also reported. Structural analysis of P{OC(CF3)3}3 suggests it is very rigid without significant conformational flexibility compared to the P{OC(CH3)3}3 analogue. The electronic properties of these ligands were assessed using both a method suggested by Gusev involving the CO stretching frequencies and bond lengths of a [IrCpCOL] complex. The use of experimental data; 1JPW, 1JRhP, IR data from [W(CO)5L] and M-P bond lengths (M = Ru, Rh) from [Ru(η5-C5H5)(NCMe)2-nL1+n]+[PF6]- (n = 0, 1), [RhCl(CO)L2] complexes were also employed.3 Interestingly the fluorinated phosphites; P{OCH(CF3)2}3 and P{OC(CF3)3}3 are found to have similar electronic properties to the incredibly electron-poor PF3 ligand, but with added steric bulk. In addition, preliminary investigations into the synthesis of highly fluorinated alkoxy-containing phosphonium cations which have the potential to form base resistant cations have been explored. For example, oxidation of highly fluorinated alkoxy-containing phosphorus (III) ligands have also been achieved, resulting in the formation of phosphonium cations such as [MePPh2OCH(CF3)2]+[O3SCF3]-. In addition to new cations, the potential for P(V)-alkoxides to form new WCAs has been explored. For example, the synthesis of a novel suprafluorophosphate anion, [P{OCH(CF3)2}5F]- has been investigated. This anion has been isolated as the following novel salts; [Ag(NCMe)4]+[P{OCH(CF3)2}5F]-, [Na(NCMe)6]+[P{OCH(CF3)2}5F]-, [Ag(PR3)3]+[P{OCH(CF3)2}5F]-; R = Ph, iPr, Me, and [NEt4]+[P{OCH(CF3)2}5F]-, some of which are even stable towards hydrolysis at room temperature. This suggests there is potential for the [P{OCH(CF3)2}5F]- anion to be the next generation of [PF6]- type anion.