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. * For communication II, see [1].The range of 31 P chemical shifts is known to exceed 500 ppm, which ensures high informative value of 31 P NMR spectroscopy in structural studies on organophosphorus compounds [2, 3]. One of the most interesting aspects of 31 P NMR spectroscopy is related to effects arising from intra-and intermolecular coordination of phosphorus to heteroatoms possessing an unshared electron pair (UEP). The effect of coordination may attain a considerable value comparable with the overall range of variation of phosphorus chemical shifts. For example, phosphorus pentachloride, which is a known electrophilic phosphorylating agent, both in crystal and in polar solvents undergoes dissociation into ions, whereas in nonpolar solvents it exists as five-coordinate phosphorus species, and the δ P value changes from -300 to 80 ppm, depending on the degree of coordination [4] (Scheme 1).In addition to available experimental data, up-todate quantum-chemical methods make it possible to get a deeper insight into the relation between δ P and the structure of organophosphorus derivatives with different coordination numbers of the phosphorus atom. 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). This process is facilitated by the presence of hydrogen chloride in the reaction mixture (via reversible hydrochlorination of the double bond. Phosphorylation of 1-vinyl-1H-pyrazole with an equimolar amount of PCl 5 favors formation of structure Z-II with six-coordinate phosphorus atom, which may be regarded as dipolar ion with intramolecular coordination.

The structure of novel phosphorus-containing N-vinylazoles prepared by action of phosphorus pentachloride has been studied by multinuclear (1)H, (13)C, (15)N, (31)P and two-dimensional (2D) NMR spectroscopy. N-vinyl-substituted 1,2-diazoles and 1,2,3-triazoles have undergone phosphorylation, exclusively, on double bond. N-vinylazoles-based hexa-coordinated phosphorus compounds have been synthesized for the first time. (31)P NMR spectroscopy provides the most convenient and unambiguous method for the investigation of E-Z-isomeric structures of phosphorylated enamines.

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Intermolecular coordination effects on the 31 P NMR spectra of molecular complexes of N-vinylimidazole and 1-allyl-3,5-dimethylpyrazole with phosphorus pentachloride were studied by theoretical and experimental methods. The formation of intermolecular dative N→P bond was shown to be accompanied by upfield shift of the phosphorus resonance signal by more than 200 ppm. Appreciable contribution of relativistic effects to 31 P NMR chemical shifts was revealed; the spin-orbital contribution to 31 P shielding constant was estimated at >210 ppm. Consideration of solvent effect was found to be crucial while studying steric structure of molecular complexes of azoles with phosphorus pentachloride and intermolecular coordination effects on 31 P NMR chemical shifts. * For communication III, see [1].We previously studied by theoretical methods the effect of intramolecular coordination on 31 P NMR shielding constants (chemical shifts) of [2-(1H-pyrazol-1-yl)ethenyl]phosphonium hexachlorophosphate(V) and 1,1,1,1-tetrachloro-1H-1λ 5 -pyrazolo[1,2-a][1,2,3]-diazaphosphol-8-ium-1-ide [1]. While developing our studies on theoretical calculations of 31 P chemical shifts [1][2][3], in the present work we examined molecular complexes of phosphorus pentachloride with some azoles, N-vinylimidazole (I) and 1-allyl-3,5-dimethylpyrazole (II). In keeping with the results of our experimental [4] and theoretical studies [1], the phosphorus atom in chlorophosphonium group is capable of forming a dative bond with pyridine-type nitrogen atom (i.e., sp 2 -nitrogen atom possessing an unshared electron pair). As a result, the coordination number of phosphorus increases to 5 or 6, and its resonance signal in the 31 P NMR spectrum is displaced upfield; therefore, 31 P NMR spectroscopy can be used to analyze structure of such intramolecular complexes.On the other hand, the presence in the heterorings of I and II of pyridine-type nitrogen atoms possessing enhanced nucleophilicity suggests that attack by phosphorus pentachloride can be directed at the heteroring with formation of the corresponding donor-acceptor molecular complexes III and IV [5, 6] (Scheme 1) rather than at the side-chain double bond. The 31 P NMR spectra of III and IV contained a singlet in the region δ P -258 to -296 ppm, which is typical of six-coordinate phosphorus atom. With a view to estimate the effect of intermolecular coordination on the 31 P shielding constants (chemical shifts) and prove the formation of dative bond in molecular complexes III and IV, we performed quantum-chemical calculations of 31 P NMR chemical shifts for the gas phase and with account taken of solvent effect (see table).The phosphorus shielding constants were calculated at the GIAO-B3LYP/DZP level of theory with account

The stereochemical structure of unsaturated phosphonic acids dichlorides containing fragments C=C-POCl 2 and C=N-POCl 2 was investigated by 31 Р NMR spectroscopy and quantum chemistry. Starting from the experimental measurement and theoretical calculation of 31 Р NMR chemical shifts confi gurations were assigned and the conformational composition of compounds under study was determined.

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Das N‐Vinyl‐octahydrocarbazol (I) reagiert mit Phosphorpentachlorid unter starker Harzbildung zu dem Hexachlorophosphat (II), das mit Schwefeldioxid in das Phosphonsäurechlorid (III) übergeht.