Quantum-chemical calculations of NMR chemical shifts of organic molecules: II. Influence of medium, relativistic effects, and vibrational corrections on phosphorus magnetic shielding constants in the simplest phosphines and phosphine chalcogenides

Abstract

The influence of solvent nature, relativistic effects, and vibrational corrections on the accuracy of calculation of 31 P chemical shifts of the simplest phosphines, phosphine oxides, phosphine sulfides, and phosphine selenides was studied. Consideration of the above factors at the stage of both geometry optimization and calculation of magnetic shielding constants was found to appreciably improve the accuracy of calculation of 31 P NMR chemical shifts in the series of phosphines and phosphine chalcogenides. * For communication I, see [1].Interest in the chemistry of phosphines and phosphine chalcogenides has increased considerably since late 1980s when direct reaction of red phosphorus with electrophiles in the presence of superbasic catalysts (Trofimov-Gusarova reaction) has been discovered [2]. This reaction made it possible to synthesize previously unknown or difficultly accessible phosphines and phosphine oxides which could be converted into phosphine sulfides and phosphine selenides [3]. The compounds thus obtained exhibited many practically important properties, and some of them are now used in the design of catalysts [4] and for the synthesis of semiconducting nanomaterials [5] and extractants for noble, rare-earth, and transuranium elements [6].In addition, phosphines and phosphine chalcogenides are classical model compounds for stereochemical studies by various physicochemical methods and up-to-date computational methods of quantum chemistry [7]. In this connection, of exceptional interest is development of procedures for theoretical calculations of spin-spin coupling constants and magnetic shielding constants (NMR chemical shifts) for phosphorus nuclei. It is known [8] that these parameters provide unique information on stereochemical structure of organophosphorus compounds.The first communication in the given series [1] was concerned mainly with calculations of 31 P NMR chemical shifts of organophosphorus compounds in the gas phase at different levels of quantum-chemical theory with the use of different basis sets. In the present work we performed a detailed study on the influence of such factors as solvation, relativistic effects, and vibrational corrections on the accuracy of calculation of phosphorus magnetic shielding constants in the series of simplest phosphines, phosphine oxides, phosphine sulfides, and phosphine selenides.All calculations of 31 P NMR chemical shifts were performed for the most favorable conformations of phosphines and phosphine chalcogenides in terms of the well known density functional theory using B3LYP functional [9, 10], following the gauge-invariant atomic orbital approach (GIAO) [11] with the Kutzelnigg IGLO-III basis set [12] (GIAO-B3LYP/IGLO-III). According to our recent data [1], this procedure ensures most accurate calculation of phosphorus chemical shifts. Search for stable conformers (including harmonic vibration analysis of localized stationary points on the potential energy surface) and optimiza-

Relativistic Effects in NMR of New Prospective Water-Soluble Ligands SeP(CH2OH)3 and H[Se2P(CH2OH)2]

“…Most likely, that is because of effects of the environment (especially taking into account that the compound exists as anion in the solution) which may have a great impact on 13 P NMR shifts [41,42]. Another possible reason is that we do not take into account Table 1 Spin-spin coupling J P,Se for selenides of some phosphines characterizing the donor-acceptor properties vibrational corrections, which also affect NMR shifts [41,43]. These effects may also be the reason why calculated J P,C and J P,H spin-spin constants are that different from the experimental values.…”

Quantum-chemical calculation of NMR chemical shifts of organic molecules: III. Intramolecular coordination effects on the 31P NMR chemical shifts of phosphorylated N-vinylazoles

“…In this work, the 31 P NMR shielding constants were calculated in terms of the density functional theory (DFT) using B3LYP functional [6,7] according to the gauge-including atomic orbital (GIAO) approach [8]. We previously found [1] that relativistic effects are crucial in the calculations of δ P for molecules containing 3rd and larger Period elements [1]. For instance, the spin-orbital contribution to δ P for trimethylphosphine sulfide and trimethylphosphine selenide attains 10 and 40 ppm, respectively.…”

“…The present communication continues the series of studies involving ab initio calculations on shielding constants [1,5]; in this work we examined effects of intramolecular coordination of the phosphorus atom in trichloro[2-(1H-pyrazol-1-yl)ethenyl]phosphonium hexachlorophosphate(V) (I) and 1,1,1,1-tetrachloro-1H-1λ 6 -pyrazolo[1,2-a][1,2,3]diazaphosphol-8-ium-1-ide (II). Phosphorylation of 1-vinyl-1H-pyrazole with PCl 5 gave Z isomer of salt I, which was stable at room temperature; it underwent Z-E isomerization at elevated temperature (Scheme 2).…”

“…Relativistic effects and effects of the medium are determining in the theoretical calculation of 31 P NMR chemical shifts. * For communication II, see [1].…”

“…Abstract-Theoretical and experimental studies on magnetic shielding of the phosphorus nucleus in trichloro-[2-(1H-pyrazol-1-yl)ethenyl]phosphonium hexachlorophosphate(V) and 1,1,1,1-tetrachloro-1H-1λ 6 -pyrazolo-[1,2-a] [1,2,3]diazaphosphol-8-ium-1-ide showed that intramolecular coordination of the phosphorus atom in the chlorophosphonium group to the nitrogen atom in the pyrazole ring leads to upfield shift of the phosphorus signal (to δ P 170 ppm) and that the contribution of the spin-orbital contribution to the 31 P chemical shift reaches 15%. Relativistic effects and effects of the medium are determining in the theoretical calculation of 31 P NMR chemical shifts.…”