Phosphorus–fluorine chemistry. Part XXXIV. Fluorophosphoranes involving potential intramolecular donor–acceptor interaction. Crystal and molecular structure of the product of the reaction of phosphorus pentafluoride with 2-methyl-8-trimethylsiloxyquinoline

Abstract

Fluorophosphoranes (RPF4; R = F, Me, Et, or Ph) reacted with 8-trimethylsiloxyquinolines to give yellow-green monosubstituted oxinato-fluorophosphoranes, stable at 20°in vacuo which, on the basis of 31P n.m.r. data, displayed the previously unobserved intramolecular N→P co-ordinate bond. The stability of this bond decreased with decreasing electronegativity of the ligand R, so that the product of the reaction between 8-trimethylsiloxyquinoline and trifluorodimethylphosphorane showed no evidence of six-co-ordination. Crystals of the complex F4P(oxMe)(oxMe = 2-methyl-8-oxyquinoline) are monoclinic, space group P21/m, with a= 8·258(4), b= 6·803(3), c= 9·453(4)A, β= 106·97(5)°, Z= 2. The molecule possesses a crystallographic plane of symmetry; co-ordination around phosphorus is almost perfectly octahedral. The N→P co-ordinate bond length [1·91l(4)A] is much longer than the N–P σ bond distance (1·769 A). The structure was solved by direct methods and refined to R 0·051 for 816 unique reflections recorded on a linear diffractometer.