Kerstin Krüger

Diselenadiphosphetandiselenide und Triselenadiphospholandiselenide - Synthese und Charakterisierung mittels31P- und77Se-Festkörper-NMRSpektroskopie

1,3-Diselena-2,4-diphosphetan-2,4-diselenide, (RPSe2)2, mit R = Me, Et, t-Bu, Ph, 4-Me2NC6H4, 4-MeOC6H4 wurden nach verschiedenen Methoden hergestellt. Von den unloslichen Verbindungen wurden 31P- und 77Se-CP-MAS-Seitenbandspektren aufgenommen. Auf diese Weise konnte die Reinheit kontrolliert und an Hand der isotropen und anisotropen Werte der chemischen Verschiebungen sowie der Kopplungskonstanten 1JP–Se die Struktur der untersuchten Verbindungen bewiesen werden. Auserdem wurden zwei unter ahnlichen Synthesebedingungen entstehende 1,2,4-Triselena-3,5-diphospholan-3,5-diselenide, (RPSe2)2Se (R = Me, Et), untersucht, von denen die Struktur sowohl aus den 77Se-Satelliten der 31P-Losungsspektren als auch aus Festkorperspektren abgeleitet wurde. Am Beispiel von (t-BuPSe2)2 wurden die experimentell aus den Seitenbandspektren ermittelten Hauptachsenwerte der Phosphor- und Selen-Abschirmtensoren mit den aus IGLOBerechnungen (HF und SOS-DFPT) erhaltenen Werten verglichen und die aus den Berechnungen ermittelten Hauptachsenlagen diskutiert. Diselenadiphosphetane Diselenides and Triselenadiphospholane Diselenides – Synthesis and Characterization by 31P and 77Se Solid-State NMR Spectroscopy 1,3-Diselena-2,4-diphosphetane-2,4-diselenides (RPSe2)2 with R = Me, Et, t-Bu, Ph, 4-Me2NC6H4, 4-MeOC6H4 have been synthesized by different methods. The insoluble compounds were investigated by 31P and 77Se solid-state NMR and the purity of the compounds has been checked by their CP MAS sideband NMR spectra. The structure of the investigated compounds has been confirmed by the isotropic and anisotropic values of the chemical shifts and the 1JP–Se coupling constants. In addition, two new 1,2,4-triselena-3,5-diphospholane-3,5-diselenides, (RPSe2)2Se (R = Me, Et), formed under similar synthesis conditions, were investigated. Their structure was derived from the 77Se satellites of 31P solution spectra and from solid-state spectra. For (t-BuPSe2)2 the experimentally obtained principal values of phosphorus and selenium shielding tensors are compared with values from IGLO calculations (HF und SOS DFPT). The calculated orientations of the principal axes are discussed.

Anisotropy of chemical shift and J coupling for P-31 and Se-77 in trimethyl and triphenyl phosphine selenides

The 31P and 77Se magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments for selenium-77 enriched (70%) trimethylphosphine selenide 1 and triphenylphosphine selenide 2 were carried out in order to determine the nuclear magnetic shielding tensors of both nuclei and to establish values of the phosphorus-selenium indirect spin-spin coupling anisotropy delta J. The m = +1/2 and m = -1/2 subspectra were analysed by the dipolar-splitting-ratio method of Eichele and Wasylischen. For the C(S) molecule 1, delta J was obtained to be +640 +/- 260 Hz from the 31P spectrum and +550 +/- 140 Hz from the 77Se spectrum. Density functional theory (DFT) calculations give a delta J value of about +705 Hz. The value of delta J could not be determined unambiguously by analysis of the 31P spectra for the C1 molecules 2; nevertheless, an estimation of delta J was possible. The principal axis 3 of the phosphorus shielding tensor was determined to be nearly parallel to the PSe bond in 1 and 2. For the selenium shielding of 1, the same orientation was found, whereas in 2, the principal axis 2 of the selenium shielding was found to be oriented nearly along the PSe bond. The experimentally determined phosphorus nuclear magnetic shielding tensors agree well with those calculated by the IGLO method. For those two principal values of the selenium-shielding tensors corresponding to directions nearly perpendicular to the SeP bond, the agreement between calculated and experimental values is satisfactory. For the third one, corresponding to the principal axis close to the SeP bond, the calculated deshielding contributions are distinctly too small for both compounds investigated. Trends observed for the calculated molecular orbital (MO) contributions to the shielding as well as possible reasons for the underestimation of the deshielding contributions along the SeP bond are discussed.

Solid-state nuclear magnetic resonance investigations on chlorocyclophosphazenes

The present study deals with solid-state nuclear magnetic resonance (NMR) investigations on hexachlorocyclotriphosphazene (N3P3Cl6) and T and K form of octachlorocyclotetraphosphazene (N4P4Cl8). Using 31P NMR we have recorded spectra of different magic-angle spinning (MAS) frequencies and static powder spectra. By means of the analysis of spinning sideband intensities the isotropic chemical shifts and the principal values of the chemical shift tensor could be determined. Because of the interactions between phosphorus and the neighbouring chlorine nuclei in the MAS spectra of N3P3Cl6 and N4P4Cl8 more lines were found to exist than was expected with regard to the isotropic chemical shift values according to the crystallographic phosphorus positions. To support this evidence solid-state spectra of the geminally disubstituted compound 2,2,4,4-tetrachloro-6,6-bisthiophenylcyclotriphosphazene [N3P3Cl4(SPh)2] were used. In addition, by means of the individual gauched localized orbitals (IGLO) method 31P NMR chemical shifts, principal values and the orientation of the principal axes of the shielding tensor were calculated for the chlorocyclophosphazenes.

Crystal structure, nuclear magnetic resonance spectroscopy and individual gauge for localised orbitals (IGLO) calculations of C6H4P2S6, a new tetrathiadiphosphorinane, and comparison with related P–S compounds

The reaction of 1,2-diphosphinobenzene with sulfur yielded a new constitution of a tetrathiadiphosphorinane ring: 4,6-(1,2-phenylene)-4,6-dithioxo-1,2,3,5,4λ5,6λ5-tetrathiadiphosphorinane the crystal structure of which has been determined, orthorhombic, space group Pbca(no. 61), a= 12.846(4), b= 16.929(7), c= 11.178(6)A and Z= 8. The tetrathiadiphosphorinane ring has a chair structure with axial positions of the 1,2-phenylene carbons and equatorial positions of the terminal sulfur atoms. One molecule per unique volume is an independent structural unit. This is consistent with the fact that the solid-state 31P cross-polarisation magic angle spinning (CP MAS) NMR spectra give two sets of slightly different principal values of the nuclear magnetic shielding tensor. A comparison with the crystal structure and the solid-state NMR data of trans-2,4-diphenyl-2,4-dithioxo-1,3,2λ5,4λ5-dithiadiphosphetane and cis-2,4-(1,8-naphthalenediyl)-2,4-dithioxo-1,3,2λ5,4λ5-dithiadiphosphetane shows that the nuclear shielding does not only depend on the molecular structure. Short intermolecular S ⋯ S distances lead to deshielding effects on the 31P nucleus. Results of individual gauge for localised orbitals (IGLO) calculations of the 31P nuclear shielding of isolated molecules agree, nevertheless, satisfactorily with the experimental principal values and additionally allow the determination of the orientation of the principal axes in the molecular framework. The IGLO calculations indicate that the principal 3 axis for the most shielded principal value lies nearly parallel with the PS bond.

METHYLTRITHIOPHOSPHONIC ACID AND RELATED COMPOUNDS - SYNTHESIS, SOLUTION, AND SOLID-STATE NMR SPECTROSCOPY AS WELL AS SHIELDING TENSOR CALCULATIONS

Abstract Methyltrithiophosphonic acid (1) has been prepared in a pure state. The thermal decomposition of 1 into 2,4-dimethyl-2,4-dithio-1,3,2,4-dithiadiphosphetane (3) proceeds via dimethylpentathiodiphosphonic acid (2), which has been characterized by its 1H and 31P high resolution NMR parameters and by a derivatization reaction with norbornadiene. Solid-state 31P CP MAS spectra of 1, 3, and the related compounds, 3,5-dimethyl-3,5-dithio-1,2,4,3,5-trithiadiphospholane (4), and 3,6-dimethyl-3,6-dithio-1,2,4,5,3,6-tetrathiadiphosphorinane (5), have been measured. The experimentally determined phosphorus anisotropic shielding tensors are compared with results of IGLO calculations. From a comparison of the experimental values with those calculated for different geometry optimized conformations of 1, 4, and 5 structural assignments became possible: In the solid state 1 most probably shows a trans orientation of the H-S-P─S unit, 4 probably realizes a half-chair and 5 a chair conformation, both with bisaxial ...

SOLID-STATE NMR STUDIES AND CRYSTAL STRUCTURE OF THE LAWESSON-REAGENT

Abstract X-ray diffraction of the toluene solvate of the Lawesson reagent, C14H14O2P2S4.C7H3, gives the following crystal data: triclinic, PT (no. 2). a = 6.831 (2), b = 9.393 (3), c = 9.793 (3) A, α = 70.33 (2), β = 83.28 (2). γ = 71.35 (2)°, V = 560.6 A3, Z = 1, and D2 = 1.471 Mg m−3. The bond lengths and angles are very close to those observed in the solvent-free crystals. The toluene molecule is disordered over two positions related by an inversion center. The asymmetric unit consists of half the formula unit. This is consistent with the fact that the solid-state 31P CP MAS NMR spectrum gives one set of principal values of the nuclear magnetic shielding tensor. Similar values were obtained for solvates of other aromatic compounds such as benzene, o-dichlorobenzene, methoxybenzene and p-dimethoxybenzene. A comparison with the data for the solvent-free Lawesson reagent shows that the nuclear shielding depends not only on the molecular structure but can also be influenced by short intermolecular S==S dis...

CRYSTAL STRUCTURE, SOLID-STATE NMR STUDIES AND IGLO CALCULATIONS OF 1-HYDROXYCYCLOHEXANEPHOSPHONIC ACID

Abstract X-ray diffraction of 1-hydroxycyclohexanephosphonic acid, C6H13O4P, gives the following crystal data: orthorhombic, P212121 (no. 19), a = 6.558(1), b = 7.644(2), c = 16.271(1) A, V = 815.65 A3, Z = 4, and Dx = 1.467 g/cm3. The molecular structure shows a chair conformation of the cyclohexane ring with the phosphonate group in equatorial position. The asymmetric unit consists of the formula unit. Solid-state 31P CP MAS NMR spectroscopy of different crystallization fractions of the title compound gives two sets of principal values of the nuclear magnetic shielding tensor caused by different modifications of the acid. According to IGLO caculations the most shielded component is almost along the P[dbnd]O bond. The results are compared with the principal values of some other C6 phosphonic acids.

Density Functional Theory, Calculations of Potential Energy Surfaces and Reaction Paths

The Density-Functional-Theory (DFT) [1] is an alternative to the traditional wave function based methods, such as Hartree-Fock plus Configuration Interaction or many-body perturbation theory, for calculations of the potential energy surfaces of molecules. In principle, this formalism allows to solve the many body problem of the electron-electron interaction through a set of quasi one particle Schrodinger-like equations — the Kohn-Sham equations [2]. In practice, approximations for the consideration of exchange and correlation energy are necessary. The so-called local density approximation (LDA) [2] was used mostly for an approximate treatment of exchange and correlation. The LDA seems to be a useful tool for handling of many electron systems like molecules. Originally, a domain of solid state physics since the pioneering investigations on molecules by Gunnarsson, Harris, Jones, Baerends and Ellis in the 1970’s [3, 4, 5] the DFT-LDA has become increasingly attractive for chemical systems, and in this way, also for studying chemical reactions. This holds essentially true due to the success of the corrections to LDA by the gradient corrections [6, 7]. One advantage of the DFT is a much lower computational effort required for the calculations of rather large molecules, compared with the “post-Hartree Fock methods” like Configuration Interaction or many body perturbation theory. Several computer codes for DFT calculations of molecules have been developed- as to review, see e.g. [8l.

31P SOLID STATE NUCLEAR MAGNETIC RESONANCE INVESTIGATIONS ON SUBSTITUTED ETHYLMERCAPTOCYCLOTETRAPHOSPHAZENES

Abstract The present study deals with 31P magic angle spinning solid state nuclear magnetic resonance (NMR) investigations on various substituted ethylmercaptocyclotetraphosphazenes. Through analyses of spinning side band intensities the isotropic chemical shifts, the principal values of the magnetic shielding tensor, the span and skew could be determined and interpreted with regard to the different substituents of the compounds. In addition, the crystal structural parameters of N4P4Cl4(SC2H5)4 were determined by X-ray structural analysis. Using these parameters 31P NMR chemical shifts and the principal values of the magnetic shielding tensor were calculated by the individual gauged of localized orbitals (IGLO) method.

2-THIOXO-1,3,2-DITHIAPHOSPHOLANES -SOLID-STATE MAS NMR AND CRYSTAL STRUCTURE INVESTIGATIONS AS WELL AS IGLO CALCULATIONS OF 31P SHIELDING TENSORS

Abstract 2-Thioxo-1,3,2-dithiaphospholanes with P-substituents R = Me, Et, i-Pr, t-Bu, Ph, 3,5-Me2C6H3, and 4-MeOC6H4 were prepared and characterized by solution and high resolution solid-state 31P and 13C NMR spectroscopy. The influence of different alkyl and aryl substituents at the phosphorus atom on the anisotropy of 31P chemical shift and on the molecular structure is discussed. The orientation of the principal axes with respect to the molecular frame is predicted from the solid-state 31P NMR results. Quantum chemical calculations of the 31P shielding tensors by the IGLO method confirm these results. The crystal structures of 2-tert-butyl-2-thioxo-1,3,2-dithiaphospholane and 2-(3,5-dimethylphenyl)-2-thioxo-1,3,2-dithiaphospholane are presented and discussed.