A study of NMR chemical shielding in 5-coordinate phosphorus compounds (phosphoranes)

Calculations of the phosphorus NMR chemical shielding in 5-coordinate phosphorus compounds have been carried out using the gauge-including-atomic-orbital (GIAO) 6-311 + G(nd,p) basis set at both scaled density functional theory (sDFT) and estimated infinite order Moller-Plesset (EMPI) approaches. Results are generally in accord with previous studies on 3-coordinate phosphor-us compounds but fail badly for compounds containing multiple chlorine atoms and indicate a need for a relativistic treatment of these species. We observe that some compounds with reported experimental P-31 NMR chemical shifts far downfield of the calculated values are in fact in the range known from experiment and calculation to be in that expected for phosphonium ions; the reported structures need to be reconsidered. (c) 2005 Elsevier Ltd. All rights reserved.