Synthesis and Application of a Bidentate Ligand Based on Decafluoro‐3‐phenyl‐3‐pentanol: Steric Effect of Pentafluoroethyl Groups on the Stereomutation of O‐Equatorial C‐Apical Spirophosphoranes

1,1,1,2,2,4,4,5,5,5‐Decafluoro‐3‐phenyl‐3‐pentanol was prepared by a Cannizzaro‐type disproportionation reaction, and the dimetallated compound was used as a bidentate ligand, which is bulkier than the Martin ligand (1,1,1,3,3,3‐hexafluoro‐2‐phenyl‐2‐propanol). A P? H spirophosphorane was synthesized by utilizing the new bidentate ligand, and the structure of the product was essentially the same as that of the P? H phosphorane with Martin ligands. Phosphoranes that exhibit reversed apicophilicity (O‐equatorial) were also synthesized and could be converted into the corresponding stable stereoisomers (O‐apical). The crystal structures of O‐equatorial phosphoranes and the O‐apical isomers were slightly affected by the steric repulsion of pentafluoroethyl groups. Kinetic measurements revealed that the stereomutation of O‐equatorial methylphosphorane to the O‐apical isomer was slowed. The activation enthalpy for the stereomutation of the former to the latter was higher than that of the phosphorane with Martin ligands by 5.1 kcal mol^?1.