Synthesis and¹⁷O Nmr Spectroscopy of a Series of¹⁷O Labeled Triarylphosphine OXIDES

Abstract

A series of nine 17 O labeled triarylphosphine oxides [(pwas synthesized, 17 O NMR spectroscopic studies were carried out (toluene solvent / 95 °C and CDCI3 / 60 °C) and the spectrum was fit with two Lorentzian peaks. The chemical shifts range from 5 51.8 to 55.7 in toluene and 8 44.8 to 48.9 in CDCI3, while ^p o varies from 159.6 to 168.6 Hz in toluene. The data were fit to the Taft DSP and Hammett equations and related to other NMR parameters for this system and the analogous X 5 -phosphazenes [(p-R-C6H 4 ) 3 PNPh]. Using the Taft DSP equation the 17 O substituent chemical shifts gave pj and p R with opposite signs which is different from what is observed with the X 5 -phosphazenes. VpQ. on the other hand correlates best with the Hammett a+ constants. The data are consistent with a triple bond contribution to the PO bonding.