Phosphinodefluorination of polyfluorobenzenes by silylphosphines Ph(R)PSiMe3 (R = Me, Ph): Further experimental and computational evidences for the concerted ANDN mechanism of aromatic nucleophilic substitution

Trimethylsilylphosphines PhRPSiMe3 (1 R = Me, 2 R = Ph) have been shown to phosphinodefluorinate 1,2,3- (3), 1,3,5- (4) and 1,2,4-trifluorobenzene (5) in benzene solution or without solvent at 150–200 °C to form the respective (difluorophenyl)methylphenyl- and -diphenylphosphines in high NMR yields under harder conditions compared to the previously reported reactions of Me2PSiMe3 with the same substrates. Hexafluorobenzene (6), pentafluorobenzene (7) (at 150 °C), octafluorotoluene (8) and pentafluoropyridine (9) (at 20 °C) react with phosphine 2 without a solvent almost quantitatively under fluorine 1,4-disubstitution (for 6) or monosubstitution (for 7–9) by the Ph2P group to give the corresponding (polyfluoroaryl)diphenylphosphines in 50–60% (for 6–8) and 95% (for 9) isolated yields. The regio and substrate selectivities exhibited by 3–5 in the reactions of the single substrates and in competitive reactions of 3 vs. 4 with 1 or 2 and 4 vs. 5 with 2 indicate relative fluorine substituent rate factors fo-F > fm-F consistent with the concerted ANDN mechanism which is supported by high level quantum chemical DFT-studies for the reactions of the substrates 3 and 4 with 1, 2 and 10 as well as for 6 with 2.