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Phenylfluorophosphoranes: axial-equatorial fluorine exchange in RC6H4PF3H and intermolecular exchange in the PhPF2(H)OMe-MeOH-base system
Kruczynski, Leonard J.,Lemire, Alberta E.,Marat, Kirk,Janzen, Alexander F.
, p. 488 - 491 (2007/10/02)
Activation parameters for axial-equatorial fluorine exchange in arylfluorophophoranes PC6H4PF3H, where R = o-CF3, m-CF3, m-CH3, were studied by the dynamic nmr technique. Δ G298(excit.) varied between 53 and 56 kJ mol-1.The synthesis of difluoromethoxyphenylphosphorane, PhPF2(H)OMe, from PhPF2 and MeOH is catalyzed by small amounts of Et3N, pyridine, PhPF3H, or HF.Rapid intermolecular ligand exchange occurs in PhPF2(H)OMe after addition of methanol and a base such as triethylamine or pyridine.Under these conditions, exchange of fluorine, hydrogen, and methoxy ligands occurs, as shown by 1H, 19F, and 31P nmr.From a line shape analysis of the 31P nmr spectrum, the rate of P-F cleavage was found to be first order (1.17 +/- 0.2) in Et3N concentration, with Δ G(excit.)298 = 50 kJ mol-1 and Δ S (excit.) = -67 J mol-1 deg-1.An equilibrium constant of 1.8 at 25 deg C was found for the reaction of PhPF2(H)OMe with PhPF2.
