Phosphorus-fluorine chemistry. Part XXVI. Phosphoranes involving the 1,3,2-dioxa-4,5-benzophosphole ring system
Reaction of o-phenylenedioxybis(trimethylsilane) with fluorophosphoranes, RnPF5-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.