Phosphorus-fluorine chemistry. Part XXVI. Phosphoranes involving the 1,3,2-dioxa-4,5-benzophosphole ring system

Abstract

Reaction of o-phenylenedioxybis(trimethylsilane) with fluorophosphoranes, R_nPF_5-n(n= 0, 1, 2, 3) was found to permit ready attachment of one (n= 2, 3; i.e. in the case of R₂PF₃ or R₃PF₂) or two (n= 0, 1; i.e. PF₅ and RPF₄) catechol rings onto five-co-ordinate phosphorus. The pinacol ester of phenylphosphonic acid, instead of a five-co-ordinate species, was obtained in the reaction of 4,4,5,5-tetramethyl-1,3-dioxa-2-silacyclopentane with phenyltetrafluorophosphorane. The resultant phosphoranes, (C₆H₄O₂)₂PF, RP(O₂C₆H₄)₂, R¹R²PF(O₂C₆H₄), and R₃P(O₂C₆H₄), were characterized by ¹H, ³¹P and, where appropriate, ¹⁹F n.m.r. spectroscopy. The stereochemistry of these compounds follows the previously established pattern, i.e. the catechol group occupies one axial and one equatorial position in a trigonal-bipyramidal framework. Because of this requirement, the compound (C₆H₄O₂)PF is exceptional in that the single fluorine atom is located in an equatorial site.