A Convenient,Selective Synthesis of Bis[2,4‐bis(trifluoromethyl)phenyl]phosphane Derivatives Starting from 1,3‐Bis(trifluoromethyl)benzene

The reaction of the sterically shielded phosphane derivative, dichlorodiethylaminophosphane, Cl₂PNEt₂, with an excess of a mixture of 2,6‐bis(trifluoromethyl) and 2,4‐bis(trifluoromethyl)phenyl lithium gives bis[2,4‐bis(trifluoromethyl)phenyl]diethylaminophosphane, [2,4‐(CF₃)₂C₆H₃]₂PNEt₂, in 72 % yield as a colourless solid, while 2,6‐bis(trifluoromethyl)phenyl lithium remains unchanged in solution. The amino derivative crystallizes in the monoclinic space group P2₁/c (a 869.2(1), b 1857.4(1), c 1357.6(1) pm, β 100.57(4)°, Z = 4). Treatment of [2,4‐(CF₃)₂C₆H₃]₂PNEt₂ in CHCl₃ solution with conc. HCl allows the synthesis of [2,4‐(CF₃)₂C₆H₃)]₂PCl. [2,4‐(CF₃)₂C₆H₃]₂PCl reacts with H₂O in THF solution with quantitative formation of the corresponding secondary phosphane oxide. To obtain bis[2,4‐bis(trifluoromethyl)phenyl]phosphinic acid, [2,4‐(CF₃)₂C₆H₃]₂P(O)OH, quantitatively, a CHCl₃ solution of [2,4‐(CF₃)₂C₆H₃]₂P(O)H, has to be stirred in an NO₂ atmosphere. The phosphinic acid crystallizes is the triclinic space group (a 754.2(1), b 927.6(2), c 1305.5(2) pm, α 85.11(2)°, β 75.45(1)°, γ 79.99(2)°, Z = 2). From the reaction of the phosphinic acid with either elemental sodium or with cyanide salts, the corresponding phosphinate salts are obtained in an almost quantitatively yield.