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

Abstract

The effects of intramolecular and intermolecular coordination on (31)P 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 (31)P nuclear shielding amounting to approximately 150 ppm on changing the phosphorous coordination number by one. A major importance of solvent effects on (31)P 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 (31)P NMR chemical shifts, provided relativistic corrections are taken into account, the latter being of crucial importance in the description of (31)P nuclear shielding.

Quantum chemical calculations of31P NMR chemical shifts: scopes and limitations

“…53,55 Intra-or intermolecular coordination involving phosphorus results in a dramatic 31 P nuclear shielding amounting to approximately 150 ppm upon changing the phosphorus coordination number by one. Namely, if molecules in solution are prone to association or selfassociation, the isolated molecular model will not be correct.…”

“…[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] In several systematic studies it was shown 48-55 that a satisfactory agreement between calculations and experiments is observed when quite a ''heavy'' basis set or high level of theory ‡ was used although deviations and exceptions were also found. In fact, there are relatively few reports on 31 P NMR CS calculations using quantum chemical methods.…”

Recent advances in computational 31P NMR: Part 1. Chemical shifts

“…Specific solvation of 93( E ) , 93( Z ) , and 94( Z ) with nitromethane reported by Chernyshev, et al had been investigated by adding several molecules of CH 3 NO 2 into solvation cavity, the latter in turn being polarized within the IEF‐PCM scheme, thereby accounting for the electrostatic, dispersion–repulsion, and cavitation nonspecific solvation effects. It followed that 31 P NMR chemical shifts calculated for isolated molecules were in a reasonably good agreement with experiment for 93( E ) and 94( Z ) , whereas in the case of 93( Z ) , theoretical values exceeded experiment by about 150 ppm.…”

“…A year later, Chernyshev, et al performed a systematic study of solvent effects on 31 P NMR chemical shifts in the phosphorus derivatives of N ‐vinylimidazole ( 92 ) in its intermolecular complexes with phosphorus pentachloride, the products of its phosphorylation, namely, tetra‐, penta‐, and hexacoordinated N ‐vinylpyrazoles 93( E ) , 93( Z ) , and 94( Z ) shown in Scheme . It was demonstrated that either intramolecular or intermolecular coordination involving phosphorus results in a dramatic 31 P NMR shielding amounting by as much as 150 ppm on changing phosphorus coordination number by one, which indicated the major importance of solvent effects on 31 P NMR chemical shifts of intramolecular and intermolecular complexes with N → P coordinate bond.…”

“…The phosphorylation of N ‐vinylpyrazole with phosphorus pentachloride. Adapted from Chernyshev, et al…”