A 13C, 15N and 77Se NMR Study of Some Diseleno Sulfonamides

¹³C, ¹⁵N and ⁷⁷Se NMR data are reported for ten title compounds. Some linear correlations of selenium, nitrogen and carbon chemical shifts values are described. A number of one- and two- bond ⁷⁷Se-¹³C coupling constants values are also given.     

Solid‐state NMR studies of 1,3‐imidazolidine‐2‐selenone and some related compounds

Solid‐state cross‐polarization magic angle spinning ¹³C, ⁷⁷Se and ¹⁵N NMR spectra were recorded for 1,3‐imidazolidine‐2‐selenone, its N‐substituted derivatives and some related compounds. The spinning sideband manifold intensities were used to obtain principal values of ¹³C and ⁷⁷Se chemical shift tensors. Large selenium chemical shift anisotropies were observed for these selenones. Copyright © 2003 John Wiley & Sons, Ltd.     

SEAL by NMR: Glyco‐Based Selenium‐Labeled Affinity Ligands Detected by NMR Spectroscopy

We report a method for the screening of interactions between proteins and selenium‐labeled carbohydrate ligands. SEAL by NMR is demonstrated with selenoglycosides binding to lectins where the selenium nucleus serves as an NMR‐active handle and reports on binding through ⁷⁷Se NMR spectroscopy. In terms of overall sensitivity, this nucleus is comparable to ¹³C NMR, while the NMR spectral width is ten times larger, yielding little overlap in ⁷⁷Se NMR spectroscopy, even for similar compounds. The studied ligands are singly selenated bioisosteres of methyl glycosides for which straightforward preparation methods are at hand and libraries can readily be generated. The strength of the approach lies in its simplicity, sensitivity to binding events, the tolerance to additives and the possibility of having several ligands in the assay. This study extends the increasing potential of selenium in structure biology and medicinal chemistry. We anticipate that SEAL by NMR will be a beneficial tool for the development of selenium‐based bioactive compounds, such as glycomimetic drug candidates.     

Complexation of Zn(II), Cd(II) and Hg(II) with thiourea and selenourea: A 1H, 13C, 15N, 77Se and 113Cd solution and solid-state NMR study

Zinc(II), cadmium(II) and mercury(II) complexes of thiourea (TU) and selenourea (SeU) of general formula M(TU)₂Cl₂ or M(SeU)₂Cl₂ have been prepared. The complexes were characterized by elemental analysis and NMR (¹H, ¹³C, ¹⁵N, ⁷⁷Se and ¹¹³Cd) spectroscopy. A low-frequency shift of the C=S resonance of thiones in ¹³C NMR and high-frequency shifts of N–H resonances in ¹H and ¹⁵N NMR are consistent with sulfur or selenium coordination to the metal ions. The Se nucleus in Cd(SeU)₂Cl₂ in ⁷⁷Se NMR is deshielded by 87?ppm on coordination, relative to the free ligand. In comparison, the analogous Zn(II) and Hg(II) complexes show deshielding by 33 and 50?ppm, respectively, indicating that the orbital overlap of Se with Cd is better. Principal components of ⁷⁷Se and ¹¹³Cd shielding tensors were determined from solid-state NMR data.     

Selenium-77 NMR chemical shifts of five-membered selenium and sulphur heterocycles with CSe,CS,and CO groups

This paper reports the ⁷⁷Se NMR chemical shifts of 1,3-dithiole-, 1,3-thiaselenole- and 1,3-diselenole-2-ones, -thiones and -selones, of the corresponding saturated compounds 1,3-diselenolane-2-one, -thione and -selone, and the 1,3-thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2-position. The ⁷⁷Se chemical shift values of the ring selenium and the C?Se groups are compared with the ¹³C chemical shift values of neighbouring carbon atoms. The relationships between the ⁷⁷Se chemical shifts of the C?Se groups and the wavelengths of their n→* absorption in the UV-visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution.     

77Se, 13C and 1H NMR investigations on ortho-carbonyl benzeneselenenyl derivatives

o-Carbonyl benzeneselenenyl compounds with COCH₃, CHO and COOCH₃ as carbonyl functions and SeCl, SeBr, SeSCN, SeSeCN, SeCN and SeCH₃ as selenium-containing groups, have been studied by ¹H, ¹³C and ⁷⁷Se NMR spectroscopy. The IR CO stretching frequencies of these compounds are also reported. If the SeCH₃ derivatives are excluded, the compounds mainly adopt a planar ‘cis’ conformation, due to an interaction between the CO group and the selenium atom. The range of over 800 ppm for the observed ⁷⁷Se chemical shifts makes ⁷⁷Se NMR spectroscopy a powerful tool for physical organic chemists.     

Synthesis of new functionalized organoselenium compounds by heterocyclization of selenium dihalides with pent-4-en-1-ol

The reaction of selenium dihalides with pent-4-en-1-ol has been carried out for the first time. Efficient procedures for the synthesis of previously unknown bis(tetrahydrofuran-2-ylmethyl) selenide, dihalobis( tetrahydrofuran-2-ylmethyl)-λ⁴-selanes, and bis(tetrahydrofuran-2-ylmethyl) selenoxide have been developed on the basis of this reaction. The product structures have been studied by ¹H, ¹³C, and ⁷⁷Se NMR. Bis(tetrahydrofuran-2-ylmethyl) selenide and dihalobis(tetrahydrofuran-2-ylmethyl)-λ⁴-selanes represent equimolar mixtures of two diastereoisomers which display different signals in the ¹³C and ⁷⁷Se NMR spectra. The oxidation of bis(tetrahydrofuran-2-ylmethyl) selenide with sodium periodate in methanol leads to the corresponding selenoxide consisting of 4 diastereoisomers.     

Regioselective addition of sulfur dichloride and selenium tetrachloride to diallyldimethylsilane as the method of preparation of eight-membered heterocycles containing silicon and chalcogens

The electrophilic additiob of sulfur dichloride and selenium tetrachloride to diallyldimethylsilane proceeds strictly according Markownikoff rule and results in the formation of previously unknown saturated siliconcontaining heterocycles, 5,5-dimethyl-3,7-dichloro-1,5-thiasilacyclooctane and 5,5-dimethyl-1,1,3,7-tetrachloro-1,5-selena(IV)silacyclooctane. The structure of heterocycles obtained was confi rmed by ¹H, ¹³C NMR spectra, in the case of selenium-containing heterocycle, by ⁷⁷Se NMR spectrum, among them the 2D HMBC spectrum.     

Solution and solid state NMR studies of some selenium analogues of auranofin (an anti-arthritic gold drug)

Three mixed ligand complexes of gold(I) with phosphines and selenones, [Et₃PAuSe=C<]Br as analogues of auranofin (Et₃PAuSR) have been prepared and characterized by elemental analysis, IR and NMR methods. A decrease in the IR frequency of the C=Se mode of selenones upon complexation is indicative of selenone binding to gold(I) via a selenone group. An upfield shift in ¹³C NMR for the C=Se resonance of the selenones and downfield shifts in ³¹P NMR for the R₃P moiety are consistent with the selenium coordination to gold(I). ¹³C solid state NMR shows the chemical shift difference between free and bound selenone to gold(I) for ImSe and DiazSe to be ca 10 and 17?ppm respectively. Large ⁷⁷Se NMR chemical shifts (55?ppm) upon complexation in the solid state for [Et₃PAuDiazSe]Br compared to [Et₃PAuImSe]Br (10?ppm) indicates the former to be more stable and the Au–Se bond to be stronger than in the latter complex.     

Phenylselenenylalkanes,their adducts with the dirhodium complex Rh2(MTPA)4 and ligand exchange mechanisms in solution as studied by 1H, 13C and 77Se NMR spectroscopy

Twelve secondary phenylselenenylalkanes and ‐cycloalkanes were studied by ¹H, ¹³C and ⁷⁷Se NMR spectroscopy in the presence of the chiral dirhodium complex Rh₂[(R)‐MTPA]₄ [Rh–Rh; MTPA‐H = (R)‐(+)‐methoxytrifluoromethylphenylacetic acid, Mosher's acid]. The 1 : 1 and 2 : 1 adducts were identified in solution at low temperatures. Two different mechanisms of ligand exchange, ‘switch’ and ‘replacement,’ were characterized and their energy barriers estimated and steric congestion during the exchange transitions is discussed. Coordination‐induced shifts Δδ(⁷⁷Se) are generally negative (shielding). For menthone bis(phenylselenoacetal) (7), these values indicate that a selection of the two selenium atoms occurs showing that 7 prefers complexation at the equatorial selenium atom whereas the axial selenium atom is hardly involved. Copyright © 2003 John Wiley & Sons, Ltd.     

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se-NHC Adducts**

N-heterocyclic carbene ligands (NHC) are widely utilized in catalysis and material science. They are characterized by their steric and electronic properties. Steric properties are usually quantified on the basis of their static structure, which can be determined by X-ray diffraction. The electronic properties are estimated in the liquid state; for example, via the ⁷⁷Se liquid state NMR of Se-NHC adducts. We demonstrate that ⁷⁷Se NMR crystallography can contribute to the characterization of the structural and electronic properties of NHC in solid and liquid states. Selected Se-NHC adducts are investigated via ⁷⁷Se solid state NMR and X-ray crystallography, supported by quantum chemical calculations. This investigation reveals a correlation between the molecular structure of adducts and NMR parameters, including not only isotropic chemical shifts but also the other chemical shift tensor components. Afterwards, the liquid state ⁷⁷Se NMR data is presented and interpreted in terms of the quantum chemistry modelling. The discrepancy between the structural and electronic properties, and in particular the π-accepting abilities of adducts in the solid and liquid states is discussed. Finally, the ¹³C isotropic chemical shift from the liquid state NMR and the ¹³C tensor components are also discussed, and compared with their ⁷⁷Se counterparts. ⁷⁷Se NMR crystallography can deliver valuable information about NHC ligands, and together with liquid state ⁷⁷Se NMR can provide an in-depth outlook on the properties of NHC ligands.     

77Se-NMR einiger titanocendiselenolen-metallacyclen

The first ⁷⁷Se NMR was carried out on a titanocene diselenopyrocatechol derivative with Se bonded directly to the transition metal. Surprisingly, the Ti metallacycle shows, compared with Zr, a reversed shielding effect by proceeding from the non-cyclic Se system to the five-membered Se,Se′ co-ordinated heterocycle. This reflects the different bonding system in Ti and Zr bis (cyclopentadienyl) dichalcogenolene complexes. The results are discussed on the basis of the ⁷⁷Se NMR spectra, the dynamic ¹H NMR spectra (¹H DNMR), and the V. B. and M. O. bonding theories.     

J(77Se,1H) and J(77Se,13C) couplings of seleno‐carbohydrates obtained by 77Se satellite 1D 13C spectroscopy and 77Se selective HR‐HMBC spectroscopy

Seleno‐carbohydrates are those in which the oxygen of the glycosidic bond or the hydroxyl group is artificially replaced with selenium. This substitution changes ¹H and ¹³C chemical shifts and produces spin coupling constants involving ⁷⁷Se. Coupling constants, such as ^2‐3J(⁷⁷Se, ¹H), are likely to be useful for conformational analyses of glycans because such couplings are never observed in natural glycans. Several papers have discussed the relationship between ^2‐3J(⁷⁷Se, ¹H) and conformation; however, only few reports describe ^1‐3J(⁷⁷Se, ¹³C), which could also be useful. Here, we obtain ⁷⁷Se coupling constants of seleno‐carbohydrates from ⁷⁷Se‐selective HR‐HMBC and ⁷⁷Se satellites in 1D ¹³C spectra and examine their conformations using the Newman projection scheme.     

Selenophilicity of Copper in Selenium-Carbon Bond Formation from Selenous Acid Using Cu(II)/Sn(II) Reagent

A selenium transfer reaction from selenous acid to benzyl and alkyl halides is initiated in the presence of stannous chloride and a catalytic amount of cupric chloride resulting in the formation of the corresponding diorganoselenides and/or diorganodiselenides as the major products as indicated by ¹ H, ¹³ C, ⁷⁷ Se NMR, and MS. The reaction is characterized by a dual-metal effect at the selenium activation and transfer step. Thus, initial reaction of stannous chloride, cupric chloride, and selenous acid gives rise to α-Cu ₂ Se. Selenium transfer from the latter to the organic halide takes place with additional assistance of stannous chloride.     

Solution and solid-state NMR studies of some cadmium-selenone complexes

Cadmium(II) complexes of Imidazolidine-2-selenone (ImSe) and its derivatives have been prepared with the general formula Cd(RImSe)2Cl2 (where R=Me, Et, Pr, etc.). These complexes are characterized by elemental analysis, IR and NMR (1H, 13C, 77Se and 113Cd) spectroscopy. An upfield shift in C=Se resonance of selenones in 13C NMR and in 77Se and high-frequency shifts in N-H resonances in 1H are consistent with the selenium coordination to Cd(II). The 77Se nucleus in Cd(ImSe)2Cl2 is shielded by 38 ppm on coordination, relative to the free ligand. The principal components of the 77Se, 113Cd and 13C shielding tensors for the complexes were determined from solid-state NMR data. Large selenium chemical shift anisotropies were observed for these complexes.     

Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants studied at the SOPPA(CC2) level taking into account relativistic corrections

A systematic theoretical study of geminal and vicinal ⁷⁷Se–¹³C spin–spin coupling constants in the series of the open‐chain selenides and selenium‐containing heterocycles revealed that relativistic effects play an essential role in the selenium–carbon coupling mechanism, especially when the coupling pathway includes a triple bond, contributing to about 10–15% of their total values and noticeably improving the agreement of the calculated couplings with experiment. Both geminal and vicinal ⁷⁷Se–¹³C spin–spin coupling constants show marked stereochemical behavior as documented by their calculated dihedral angle dependence that could be used as a practical guide in stereochemical studies of organoselenium compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

Full four‐component relativistic calculations of the one‐bond 77Se–13C spin‐spin coupling constants in the series of selenium heterocycles and their parent open‐chain selenides

Four‐component relativistic calculations of ⁷⁷Se–¹³C spin–spin coupling constants have been performed in the series of selenium heterocycles and their parent open‐chain selenides. It has been found that relativistic effects play an essential role in the selenium–carbon coupling mechanism and could result in a contribution of as much as 15–25% of the total values of the one‐bond selenium–carbon spin‐spin coupling constants. In the overall contribution of the relativistic effects to the total values of ¹J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin‐orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second‐order polarization propagator approach (CC2) with the four‐component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of ¹J(Se,C). Solvent effects in the values of ¹J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2–78.4) are next to negligible decreasing negative ¹J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of ⁷⁷Se–¹³C spin‐spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1–0.2‐Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd.     

Organylselenoacetylene und selenocyanate; 77Se- und 13C-NMR-chemische verschiebungen und 77Se- 13C-spin-kopplungskonstanten

⁷⁷Se and ¹³C NMR chemical shifts and ⁷⁷Se-¹³C spinspin coupling constants of mono- and bis(organylseleno)acetylenes and organyl selenocyanates are shown. The changes of ⁷⁷Se chemical shifts caused by variation of the organyl groups are well reflected by known increments. The δ(⁷⁷Se) and ¹J(⁷⁷Se¹³C) values of the investigated compounds are discussed in relation to the corresponding alkyl- and vinyl-selenides. The ¹J(⁷⁷Se¹³C) values of the selenoacetylenes and selenocyanates as well as alkyl- and vinyl-selenides are linearly dependednt (i) on ¹J(¹³C¹H) values of the corresponding hydrocarbons, hydrogen cyanide respectively and (ii) on the product of the s-characters of the coupled Se and C atoms. These linear correlations prove the predominance of the Fermi contact term for changes of the one-bond ⁷⁷Se¹³C coupling in dependence on hybridization.     

Synthesis and Characterization of Unsymmetric 4-Picolyl Selenides

A number of unsymmetrical heteroaryl 4-picolyl selenides have been prepared by lithiation of 4-picoline using lithium diisopropylamide under cryogenic conditions. The intermediate 4-lithiopicoline formed was then reacted with elemental selenium followed by the addition of suitable electrophiles to give 4-picolyl alkyl selenides. 4-Lithiopicoline was also made to react directly with diaryl/dibenzyl diselenide to yield mixed 4-picolyl aryl/benzyl selenides. All these hitherto unknown selenides were characterized through various spectroscopic techniques viz., NMR (¹H, ¹³C, ⁷⁷Se), IR and mass spectrometry.     

Regioselective reactions of sulfur, selenium and tellurium chlorides with allyl trimethyl silane

Electrophilic addition of SCl₂, SeCl₂ and SeCl₄ to 2 equivalents of allyl trimethyl silane proceeds regioselectively to give bis[2-chloro-3-(trimethylsilyl)propyl] sulfide, selenide and selenium dichloride, respectively. The reaction with TeCl₄ affords only diallyl tellurium dichloride. The structures of the compounds were confirmed by ¹H, ¹³C, ⁷⁷Se and ¹²⁵Te NMR techniques.