Trimethylsilyl- and trimethylstannyldimethylphosphane - Convenient and versatile reagents for the synthesis of polyfluoroaryldimethylphosphanes

Trimethylsilyldimethylphosphane (Me3SiPMe2) and the corresponding tin compo und (Me3SnPMe2) were used as reagents for the substitution of fluorine by t he Me2P group in polyfluoroarenes C6F5X (X=F, H, Cl, CF3) and C5NF5. The re actions occur even under mild conditions (T = 0 - 20 degreesC), either in b enzene or without solvent, to give as a rule 4-X-1-(dimethylphosphano)tetra fluorobenzenes (XC6F4PMe2, 1-4) and 4-(dimethylphosphano)tetrafluoropyridin e (C5NF4PMe2, 5), respectively, in yields between 75 and 95%. In the case o f C6F6, double substitution is also observed, which affords 1,4-bis(dimethy lphosphano)tetrafluorobenzene (6). A very efficient route to the compounds XC6F4PMe2 (X=F, H, Cl, CF3) and C5NF4PMe2 was developed as a one-pot reacti on of the corresponding fluoroarenes with tetramethyldiphosphane (P2Me4) an d 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 P-31 signals , revealed the influence of the substrate type on the rate of reaction in t he sequence: C5NF5>C6F5CF3> C6F5Cl, C6F5PMe2 > C6F5H > C6F6 much greater th an C6H5F. Ab initio calculations were carried out on the model reactions of pentafluoropyridine with silylphosphane, phosphane or phosphide to discrim inate between possible reaction mechanisms. The novel phosphanes were chara cterised by spectroscopic investigations (NMR, MS), by preparation of the r elated thiophosphanes ArFP(=S)Me-2 (8 - 14), their spectroscopic and analyt ic data and single crystal X-ray diffraction studies on five of these deriv atives.