Synthesis and molecular structures of fluorophosphoranes, R₃PF₂, isoelectronic with anionic fluorosilicates

Abstract

The new difluorophosphoranes Ph(o-Tol)₂PF₂ (1), Mes₃PF₂ (2), Ph(I-Np)₂PF₂ (3), (o-Tol)₃PF₂, (p-Tol₃PF₂, Ph(t-Bu)₂PF₂, and (Ph₂PF₂CH₂ containing bulky substituents were prepared by the fluorination reaction of precursor organophosphines with dimethylaminosulfur trifluoride. They were characterized by ¹H, ³¹P, and ¹⁹F NMR spectra. The molecular structures of 1-3 revealed trigonal bipyramidal geometries. Comparison of the structural data with that of isoelectronic anionic fluorosilicates along with the NMR data suggests the operation of a steric effect that increases bond lengths in the difluorophosphoranes 1-3 and in related anionic silicates. The data are discussed relative to enhanced reactivity observed for anionic silicates. 1 crystallizes in the monoclinic space group C2/c with a = 11.819(3) Å, b = 10.163(2) Å, c = 13.992(3) Å, β = 99.14(2)°, and Z = 4.2 crystallizes in the monoclinic space group C2/c with a = 10.531(2) Å, b = 12.667(2) Å, c = 18.110(4) Å, β = 104.21(2)°, and Z = 4. 3 crystallizes in the monoclinic space group P2₁/c with a = 15.868(2) Å, b = 7.434(1) Å, c = 18.213(4) Å, β = 112.34(2)°, and Z = 4. The final conventional unweighted residuals are 0.063 (1), 0.060 (2), and 0.040 (3).