Chiral water-soluble secondary phosphines (2-6) were obtained by nucleophilic phosphination of FC6H4-4-SO3K (la), FC6H3-2,4-(SO3K)(2) (Ib), and FC6H4-2-SO3K (Ic) with RPH(2) (R = Ph, 2,4,6-Me(3)C(6)H(2), 2,4,6-iPr(3)C(6)H(2)) in the superbasic medium DMSO/KOH by employing steric control of substitution at phosphorus by bulky substituents R and sulfonic groups in the ortho position of the aromatic ring systems in Ib or Ic. The secondary phosphines may be deprotonated in DMSO/KOH to give phosphido anions which on reaction with alkyl halides (PhCH(2)Cl, Br(CH2)(3)Br, and C12H25Br) yield mono- or bidentate tertiary phosphines (7-10). Ligands of this type are alternatively accessible by nucleophilic arylation of secondary phosphines, e.g. Ph(Me)PH or Ph(H)P(CH2)(3)P-(H)Ph with la or Ib, respectively. The crystal structure of the starting material 1b . H2O (space group P2(1)/m) has been determined. In the solid state of 1b . H2O the individual molecules are interconnected by ionic interactions between the potassium cations and the SO3- anions. The C-F bond (C(1)-F 1.347(4) Angstrom) is shorter than that in C6H5F (1.356(4) Angstrom). The unit cell of 7a . 0.5H(2)O (space group ), the first structurally characterized chiral phosphine with a sulfonated phenyl substituent, contains the two enantiomers. Due to the asymmetrical substitution at phosphorus the PC3 skeletons are significantly distorted (P(1)-C(1,11,31) 1.864(10), 1.825(8), 1.841(7) Angstrom). The electronic structure of sulfonated fluorobenzenes FC6H5-n(SO(3)M)(n) (M = K, NH4, n = 1-3) is discussed on the basis of quantum chemical calculations. In particular, the reactivity difference toward nucleophilic phosphination within the series is rationalized in terms of steric factors and of the -I effect of the sulfonic groups.