Synthetic and kinetic studies of the reversible addition of a bridging NSN fragment to the electron-rich heterocycles (R 2 PN)(SN) 2 (R = Me, Ph, F)

Abstract

The oxidative addition of Cl 2 (using SO 2 Cl 2 ) to the six-membered ring (R 2 PN)(SN) 2 (R = Me, Ph) produces the mixed phosphazene–thiazyl heterocycles, (R 2 PN)(NSCl) 2 , which react with Me 3 SiNSNSiMe 3 to give the bicyclic compounds R 2 PS 3 N 5 . The latter undergo thermal decomposition, at ca. 100 °C in toluene, via reductive elimination of an NSN unit to regenerate (R 2 PN)(SN) 2 in high yield. Kinetic measurements of this process, using 31 P nmr spectroscopy, yield an activation energy of 102.4 ± 6.0 kJ mol −1 for the release of the NSN fragment from Me 2 PS 3 N 5 . The thermolysis route has been used to prepare the thermally unstable (F 2 PN)(SN) 2 , characterized as a 1:1 adduct with norbornadiene.