The effects of intramolecular and intermolecular coordination on 31P nuclear shielding: phosphorylated azoles

The effects of intramolecular and intermolecular coordination on ³¹P nuclear shielding have been investigated in the series of tetracoordinated, pentacoordinated and hexacoordinated N‐vinylpyrazoles and intermolecular complexes of N‐vinylimidazole and 1‐allyl‐3,5‐dimethylpyrazole with phosphorous pentachloride both experimentally and theoretically. It was shown that either intramolecular or intermolecular coordination involving phosphorous results in a dramatic ³¹P nuclear shielding amounting to approximately 150 ppm on changing the phosphorous coordination number by one. A major importance of solvent effects on ³¹P nuclear shielding of intramolecular and intermolecular complexes involving N → P coordination bond has been demonstrated. It was found that the zeroth‐order regular approximation–gauge‐including atomic orbital–B1PW91/DZP method was sufficiently accurate for the calculation of ³¹P NMR chemical shifts, provided relativistic corrections are taken into account, the latter being of crucial importance in the description of ³¹P nuclear shielding. Copyright © 2012 John Wiley & Sons, Ltd.