Trimethylsilyl- and trimethylstannyldimethylphosphane--convenient and versatile reagents for the synthesis of polyfluoroaryldimethylphosphanes.
Trimethylsilyldimethylphosphane (Me3SiPMe2) and the corresponding tin compound (Me3SnPMe2) were used as reagents for the substitution of fluorine by the Me2P group in polyfluoroarenes C6F5X (X = F, H, Cl, CF3) and C5NF5. The reactions occur even under mild conditions (T = 0-20 C), either in benzene or without solvent, to give as a rule 4-X-1-(dimethylphosphano)tetrafluorobenzenes (XC6F4PMe2, 1-4) and 4-(dimethylphosphano)tetrafluoropyridine (C5NF4PMe2, 5), respectively, in yields between 75 and 95%. In the case of C6F6, double substitution is also observed, which affords 1,4-bis(dimethylphosphano)tetrafluorobenzene (6). A very efficient route to the compounds XC6F4PMe2 (X = F, H, Cl, CF3) and C5NF4PMe2 was developed as a one-pot reaction of the corresponding fluoroarenes with tetramethyldiphosphane (P2Me4) and trimethyltin hydride (Me3SnH) at moderate temperatures. This process was tested for C6F6 and perfluorobiphenyl which gave C6F5PMe2 (1) and 4,4'-bis(dimethylphosphano)octafluorobiphenyl (7), respectively. The results, which included kinetic measurements that used the intensities of the 31P signals, revealed the influence of the substrate type on the rate of reaction in the sequence: C5NF5>C6F5CF3> C6F5Cl, C6F5PMe2>C6F5H>C6F6>> C6H5F. Ab initio calculations were carried out on the model reactions of pentafluoropyridine with silylphosphane, phosphane or phosphide to discriminate between possible reaction mechanisms. The novel phosphanes were characterised by spectroscopic investigations (NMR, MS), by preparation of the related thiophosphanes ArFP(=S)Me2 (8-14), their spectroscopic and analytic data and single crystal X-ray diffraction studies on five of these derivatives.
Syntheses, Structures, and Redox Properties of 1,4-Bis(dimesitylphosphino)-2,3,5,6-tetrafluorobenzene and the Corresponding Bis(phosphoryl) and Bis(phosphonio) Derivatives.
Sterically hindered 1,4-bis(dimesitylphosphino)-2,3,5,6-tetrafluorobenzene (1) was synthesized by the aromatic nucleophilic substitution of lithium dimesitylphosphide with hexafluorobenzene. Two phosphorus atoms of 1 were oxidized and methylated to give the corresponding bis(phosphoryl)benzene 2 and bis(phosphonio)benzene 32+·2TfO− (TfO− = trifluoromethanesulfonyl), respectively. On the other hand, reaction of 1 with butyllithium and phenyllithium gave more crowded 2,5-dibutyl-1,4-bis(dimesitylphosphino)-3,6-difluorobenzene (4) and 1,4-bis(dimesitylphosphino)-2,5-difluoro-3,6-diphenylbenzene (5), respectively. Structures of 1, 2, 32+·2TfO−, 4, and 5 were confirmed by conventional spectroscopic methods; particularly 19F NMR spectroscopy reflected their crowded structures. Molecular structures of 1, 2, and 32+·2TfO−, were further investigated by X-ray crystallography, where unusually large bond angles around phosphorus atoms were observed. Electrochemical measurements were carried out to investigate redox p...
Electrochemical reactions of fluoro-compounds. Part II. The preparation of substituted fluoro-aromatic derivatives
2,4,5,6-Tetraflucro-1,3-phenylenediamine has been prepared by the electrochemical reduction of 1-amino-3-iminoheptafluorocyclohex-1-ene at a mercury cathode. Similarly, by reduction of other amino-imino-fluorocyclohex-1-enes and aminoheptafluorocyclohexenones, 2-trifluoromethyl-4,5,6-trifluoro-1,3-phenylenediamine, 1-amino-2,4,5,6-tetrafluorophenol, and 1-isopropylamino-2,4,5,6-tetrafluorophenol were obtained. The reduction of 1-methylamino-3-methyliminoheptafluorocyclohex-1-ene was anomalous, and gave 2,5,6-trifluoro-4H-NN′-dimethyl-1,3-phenylenediamine. 1-Amino-3-imino-pentafluorocyclopent-1-ene gave 1,3-diamino-3H-pentafluorocyclopent-1-ene without loss of fluorine. The polarographic reduction of the cyclohexene derivatives and some mono substituted heptafluorocyclohexa-1,3 and 1,4-dienes has also been investigated, and changes in E½ discussed in terms of the Hammett σp function.