Increased coordination via sulfur donor action in cyclic pentaoxyphosphoranes and the parent cyclic phosphite. Influence of pentafluorophenoxy ligands

The pentafluorophenoxy ligand was introduced into the new cyclic pentaoxyphosphoranes S[(t-Bu)MeC6H2O](2)P(OC6F5)(O2C6Cl4) (1); S [(t-BU)MeC6H2O](2)P(OC6F5)(O2C14H8) (2), and S [(t-Bu)MeC6H2O](2)P(OC6F5)(3) (3). X-ray analysis revealed hexacoordinate structures formed by sulfur donor action present as a bridging atom in flexible eight-membered rings for 1-3. X-ray analysis showed that sulfur coordination also occurred with the same type of ring system as part of the phosphite S[(t-Bu)Me6H2O](2)P(OC6F5) (4) to give a pseudo-trigonal-bipyramidal geometry. The pentafluorophenoxy ligand present in the oxyphosphoranes 1-3 as well as in the phosphite 4 acts comparably to a chlorine atom in its ability to enhance phosphorus electrophilicity as measured by the degree of P-S coordination and geometrical displacement toward a more highly coordinated state. The phosphite 4 has a P-S donor distance of 2.876(2) Angstrom, considerably longer than the range of P-S distances from 2.366(3) to 2.495(2) Angstrom obtained for the pentaoxyphosphoranes 1-3. These data express quantitatively the relative electrophilicity of phosphorus as a function of coordination number and substituent composition.