Trimethylsilyl- and Trimethylstannyldimethylphosphane—Convenient and Versatile Reagents for the Synthesis of Polyfluoroaryldimethylphosphanes

Abstract

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.

Reactions of Polyfluoroarenes with MenE-MMe3 Reagents (MenE = Me2As, Me2P, Me2N, and MeS; M = Si, Sn): Synthesis of Polyfluoroaryl MenE CompoundsDedicated to Professor Dieter Naumann on the Occasion of his 60th Birthday

“…The δ F values of the meta-F atoms are typical for the wide series of known C 6 F 5 X compounds [3]. Both the 1 H and 19 F NMR data are close to those of the phosphorus analogues [1].…”

“…In view of the air and moisture sensitivity of the reagents Me 3 SiEMe 2 (E ϭ As, P, N) and the expected polyfluoroarylphosphane derivatives, high vacuum and Schlenk techniques were used as reported earlier [1]. The reactions were monitored by the time dependence of the yields estimated on the basis of the 1 H, 19 F and 31 P NMR signal intensities of the products.…”

“…Pentafluoropyridine reacts distinctly more readily than the other substrates forming 4-dimethylarsanotetrafluoropyridine 4 at 50°C within 1 h in 94 % isolated yield. On the whole, the reactions of polyfluoroarenes with Me 3 SiAsMe 2 exhibit the same regioselectivity, but are significantly slower than those with Me 3 S-iPMe 2 which reacts at an appreciable rate even at room temperature [1].…”

“…In the reaction of hexafluorobenzene not only 1 is formed but also the product of its further conversion: 1,4-bis(dimethylarsano)tetrafluorobenzene 5 in 48 (1) and 43 % (5) isolated yield, based on the amount of Me 3 SiAsMe 2 . This result is close to that we found for the corresponding reaction of C 6 F 6 with Me 3 SiPMe 2 [1]. Therefore, it seems possible to alter the portions of the mono-and the disubstituted product in the mixture by varying the molar ratio of Me 3 SiAsMe 2 and C 6 F 6 .…”

“…We recently reported that both Me 3 SiPMe 2 and Me 3 SnPMe 2 are effective, convenient and versatile reagents for introducing Me 2 P groups into polyfluoroarenes C 6 F 5 X by replacement of the fluorine atom in para position to X [1]. Since tertiary fluoroarylarsanes also are of interest as ligands in catalytically active transition metal complexes [2] and as starting materials for the preparation of arsano-substituted derivatives of fluorinated heterocycles, e. g. dibenzodioxin, phenoxathiin, phenoxazine etc., with probably higher biological activity as compared to the unsubstituted analogues, we have studied the reactions of a number of polyfluoroarenes and perfluoropyridine with trimethylsilyldimethylarsane Me 3 SiAsMe 2 .…”