Partial Double Bond Character Research Articles

カルコゲノイミニウム塩：系統的合成と炭素‐炭素結合形成反応への応用

A variety of seleno and telluroiminium salts were obtained by reacting the corresponding seleno and telluroamides with methyl triflate at room temperature for 30s. X-ray molecular structure analysis, 13C NMR spectra, and molecular orbital calculations of seleno- and telluroiminium salts suggested that the electrons on the chalcogen atom of the salts are somewhat delocalized with respect to the iminium group, and C-Se and C-Te bonds have a partial double-bond character. Aromatic thio- and selenoiminium salts reacted with a lithium acetylide at their iminium carbon atoms, whereas the aromatic telluroiminium salt reacted at the tellurium atom. This difference in reactivity was elucidated by molecular orbital calculations of the model compounds. Based on the reactivity test of a series of chalcogenoiminium salts, two types of new reactions were developed. Alkynylation of thio- and selenoiminium salts led to α, β-unsaturated ketones. The reaction involves the [1, 3] -shift of MeS- and MeSe-groups to give aminoallenes as intermediates. Alternatively, the sequential reactions with organolithium and -magnesium reagents selectively gave propargylamines. The wide applicability of these reactions is also shown.

Acyclic Telluroiminium Salts: Isolation and Characterization

The isolation, structure, and reactions of acyclic telluroiminium salts were disclosed. The delocalization of electrons on the tellurium atom and the partial double-bond character of C-Te bonds in the salts are discussed on the basis of X-ray molecular structure analysis, 13C and 125Te NMR spectroscopy, and molecular orbital calculation.

Synthesis and Properties of Selenoiminium Salts Derived from Secondary Selenoamides

A variety of N-monosubstituted selenoiminium salts were obtained by reacting the corresponding secondary selenoamides with methyl triflate at room temperature for 30 s. All of the salts were stable under air below room temperature. The structures of the selenoiminium salts were determined by X-ray molecular analysis and compared with those of the starting selenoamide and its anionic derivative, i.e., an ammonium selenoimidate. Their benzene rings and selenoamide moieties were found to not be planar. 13C and 77Se NMR spectra of these compounds were also compared, and the results suggested that the electrons on the selenium atom of the salts are somewhat delocalized to the CN double bond and the carbon−selenium bond of the salts shows a partial double-bond character. The degree of the delocalization of the electrons can be explained by considering the electron-donating ability of the selenium atom and the electron-accepting ability of the carbon−nitrogen bond. The reaction of the selenoiminium salt with several bases gave the corresponding methyl selenoimidate in high yield. Methylation of an ammonium selenoimidate also gave the methyl selenoimidate. The Z-isomer was predominantly formed in exactly the same ratio in these different reactions. The stereochemical outcome of the formation of a methyl thioimidate formed by two different reactions is also discussed.

Synthesis of Re(I) complexes bearing tridentate 2,6-bis(7 ′-azaindolyl)phenyl ligand with green emission properties

The Re(I) complexes bearing 2,6-bis(7 ′-azaindolyl)phenyl ligand as a tridentate ligand were synthesized by treatment with Re 2(CO) 10. The structures of the complexes were confirmed by X-ray crystallography. Both 7-azaindolyl ligands of Re(I) complexes are present in butterfly forms. The Re–C ipso bonds showed a partial double bond character by π back-donation between the phenyl moiety and Re atom. In THF solution at room temperature, these complexes exhibited green emission ( λ em=510 nm), which is considered to be attributable to MLCT (dz 2(Re) →π * (7 ′-azaindolyl group)) transition containing π→π * (7 ′-azaindolyl group) transition.

Crystal and molecular structure of dibenzoyl disulfide

Crystals of dibenzoyl disulfide, C14H10O2S2, are monoclinic, space group P21/c, with the cell dimensions (294 K), a = 12.356 (1), b = 12.071 (1), c = 9.071 (2) A, β = 107.15(1)°, V =1292 (3) A3 with D m = 1.42, D x = 1.411 g ⋅ cm−3, and Z = 4. Complete three-dimensional data was collected on a CAD-4 diffractometer using the ω/2θ method, the crystal structure was solved using MULTAN and refined by full-matrix least-squares methods to a final R value of 0.036 for 2738 observed reflections. The S–S bond distance is 2.021(1) A and has a partial double-bond character. The dihedral angle around the disulfide bond is 80.8°. The two S–C distances are 1.805(2) and 1.823(2) A. The central part of the molecule (C–S–S–C) adopts a skewed nonplanar configuration and the planes of the two benzene rings are inclined at an angle of 93.7°. The S–S bond direction from the X-ray could be compared with the directions of gmin for (S–S) anion and gmax for (S–S) cation deduced from electron spin resonance spectroscopy. The former makes an angle of 4.6° and the latter makes an angle of 18.1° with the S–S bond direction.

Electronic Structure and Bonding in the Ternary Silicide YNiSi₃

An analysis of the electronic structure and bonding in the ternary silicide YNiSi 3 is made, using extended Huckel tight-binding calculations. The YNiSi 3 structure consists of Ni-capped Si 2 dimer layers and Si zigzag chains. Significant bonding interactions are present between the silicon atoms in the structure. The oxidation state formalism of (Y 3+ )(Ni 0 )(Si3) 3- for YNiSi3 constitutes a good starting point to describe its electronic structure. Si atoms receive electrons from the most electropositive Y in YNiSi 3, and Ni 3d and Si 3p states dominate below the Fermi level. There is an interesting electron balance between the two Si and Ni sublattices. Since the π * orbitals in the Si chain and the Ni d and s block levels are almost completely occupied, the charge balance for YNiSi3 can be rewritten as (Y 3+ )(Ni 2- )(Si 2- )(Si-Si) + , making the Si 2 layers oxidized. These results suggest that the Si zigzag chain contains single bonds and the Si 2 double layer possesses single bonds within a dimer with a partial double bond character. Strong Si-Si and Ni-Si bonding interactions are important for giving stability to the structure, while essentially no metal-metal bonding exists at all. The 2D metallic behavior of this compound is due to the Si-Si interaction leading to dispersion of the several Si 2 π bands crossing the Fermi level in the plane perpendicular to the crystallographic b axis.

Bis(pentafluorophenyl)borinic Acid: a Cyclic Trimer in the Solid State and a Monomer, with Hindered Rotation around the B−OH Bond, in Solution

The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C2 twist-boat conformation); dissolution in toluene-d8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal restricted rotation of the OH substituent around the Ar2B−OH bond (Ea = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.

Novel eta 3 -1-silaallyl tungsten complexes via Si-H bond activation of hydrovinylsilanes: structure and reactivity toward methanol.

Reactions of cis-Cp*(CO)2W(MeCN)Me (1) with HSiMe2(CH=CR2) (R = H, Me) afford the novel eta3-1-silaallyl complexes Cp*(CO)2W(eta3-Me2SiCHCR2) [R = H (2), Me (3)] accompanied by liberation of MeCN and CH4 via thermal Si-H bond activation. eta3-Coordination and exo conformation of the 1-silaallyl ligand in 3 are shown by X-ray crystal analysis, which reveals the partial double bond character of the Si-C bond (1.800(4) A) in the silaallyl moiety. Complexes 2 and 3 show extremely high reactivity toward MeOH to give the hydrido-(methoxysilyl)alkene complex trans-Cp*(CO)2WH(eta2-MeOMe2SiCH=CH2) (4) and the four-membered metallacycle Cp*(CO)2WCH(CHMe2)SiMe2OMe (6), respectively.

Reactivity and crystal structures of the first dithiocarbamate chromium(0) and dithiophosphate tungsten(0) complexes: crystal structures of [Et 4N][Cr(η 2-S 2CNC 5H 10)(CO) 4] and [Et 4N][W{η 2-S 2P(OEt) 2(CO) 4

The structures of first dithiocarbamate chromium(0) complex [Et 4N][Cr(η 2-S 2CNC 5H 10)(CO) 4] ( 1) and the diethyldithiophosphate tungsten(0) complex [Et 4N][W{η 2-S 2P(OEt) 2(CO) 4] ( 2) have been determined by X-ray diffraction analyses. Crystal data for 1: space group, P2 1 with a=10.240(2) Å, b=12.705(4) Å, c=9.888(2) Å, β=117.26(2)°, V=1143.6(4) Å 3, and Z=2. The structure was refined to R=0.027 and R w=0.028; Crystal data for 2: space group, C2/ c with a=13.054 (6) Å, b=16.220 (4) Å, c=11.417 (3) Å, β=93.73 (3)°, V=2412.3 (14) Å 3, and Z=4. The structure was refined to R=0.026 and R w=0.019. The geometry around the metal atom in the anion of these two complexes is a distorted octahedron. The dithiocarbamato and diethyldithiophosphato ligands, respectively, coordinate to the Cr and W metal center through the two sulfur atoms. The short CN bond length of 1.335(4) Å in 1 indicates a considerable partial double bond character. The allyl dithiophosphate tungsten complex [W(CH 3CN)(η 3-C 3H 5)(CO) 2{η 2-S 2P(OEt) 2}] ( 3) can be obtained from the reaction of [W(CH 3CN) 2(η 3-C 3H 5)(CO) 2Br] and (EtO) 2PS 2NH 4 in CH 3CN at room temperature but decomposed in the reaction of 2 with allyl bromide. Complex 3 reacted with dppe in CH 2Cl 2 at room temperature to give a mixture of complex [W(η 3-C 3H 5)(CO) 2{η 2-S 2P(OEt) 2}] 2(μ-dppe) ( 4) and [W(η 3-C 3H 5)(CO) 2{η 2-S 2P(OEt) 2(η 1-dppe)] ( 5).

Photochemistry of Anils in NaY Zeolite

A series of anils (1−6) have been incorporated in NaY zeolites and the resulting samples characterised spectroscopically. Raman spectral analysis showed that anils exist in the zeolite microcavities predominantly in a zwitterionic form. In agreement, diffuse reflectance UV/Vis spectra showed the presence of a significant concentration of the zwitterionic form, characterised by an absorption band around 400 nm. A sharp contrast is drawn between their photochemistry in solution or in the crystalline form with that in NaY zeolites. Thus, steady state irradiation at 400 nm led to persistent changes in the diffuse reflectance UV/Vis spectra with decrease of the reflectance of the band at 400 nm and the appearance of a new absorption band at longer wavelengths. No photochromism is observed and this is attributed to the isomerization of the zwitterionic form to other stereoisomers, possibly by rotation about C−C or C−N bonds with partial double bond character. This photochemical isomerization has not been reported so far. Even though the hydrogen bonding ability and polarity of NaY zeolite has been reported to be similar to that of polyfluorinated alcohols, based on the enolisation equilibrium of anils, the photochemical behaviour of these compounds incorporated within NaY is different to that reported in polyfluorinated alcohols. Specifically, no excited-state proton transfer or proton catalysed re-enolization of the zwitterionic form is observed with anils in NaY. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

1H and 13C NMR Study of 1-Hydrazino-2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-diones and -1H-pyrazolo[1,2-b]phthalazine-5,10-diones and Their Ring-Chain Tautomerism

Treatment of 1-hydroxy-2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-diones and -1H-pyrazolo[1,2-b]phthalazine-5,10-diones with hydrazides produces corresponding acylhydrazino derivatives. In this work, ten new hydrazino derivatives were synthesized, and their properties were studied by 1H and 13C NMR spectroscopy. These compounds exhibited several types of structural variation, including ring-chain tautomerism, cis-trans isomerism with respect to the substituents in the pyrazole ring, and (E)/(Z) rotamerism with respect to the nitrogen−carbon hydrazide bond with partial double-bond character. In [D6]DMSO, 2,3-dihydro-1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives were found mainly as linear tautomers, whereas 2,3-dihydro-1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives favored cyclic tautomers. For the latter compounds, a six-component equilibrium was found, consisting of a linear and of cis and trans cyclic tautomers, all of which had two rotamers, (E) and (Z). (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Silanones and metasilicates from negatively charged SiO (−) and SiO 2(2−) precursors. Theoretical study

Ab initio calculations were performed to compare the electronic effects in unionized, partly and fully ionized silanols, XH 2SiOH, and silanediols, XHSi(OH) 2, X=H, OH, OSiH 3, Cl. The delocalization energy strongly increases on ionization. The silicon bond to negatively charged oxygen is significantly shortened gaining a partial double bond character, while the adjacent bonds to geminal oxygen, chlorine and hydrogen are elongated and effectively weakened. The weakening of the SiX bond is particularly large in the dianionic structures, XHSiO 2 (2−). The delocalization energy in neutral silanols is mainly due to the negative hyperconjugation (p O→σ* SiX) π. In silanolate anions, the (p O→d Si) π delocalization becomes more important. Thermodynamic parameters were calculated for the transformation of some ionized silanols, X(HO) n H 2− n SiO (−), and silanediols, XHSiO 2 (2−) into silanones and metasilicates, respectively, by elimination of X (−). In the gas phase, the formation of silanones by this route is energetically very costly. However, thermodynamical calculations suggest that the process may occur in a polar solvent. In contrast, the formation of metasilicates is thermodynamically favoured even in the gas phase.

Thermal decomposition of energetic materials 79: Thermal, vibrational, and X-ray structural characterization of metal salts of mono- and di-anionic 5-nitraminotetrazole

The energetic alkali metal salts (Li +, Na +, K +, Rb +, Cs +) of the 5-nitraminotetrazole mono-anion(II) and di-anion(III) were synthesized and their properties compared with neutral 5-nitraminotetrazole(I). The decomposition temperatures by DSC follow the order (III)>(II)>(I), and for the salts of (III) Li +>Na +>K +>Rb +>Cs +. Both thermal stability trends are consistent with a major role played by the crystal lattice energy. Loss of H 2O is detected by TGA in cases where hydrates also form. The crystal and molecular structures of Cs(II) and Rb 3(III)(NCNNO 2)·H 2O were determined by X-ray diffraction. The latter compound is the first structural characterization of (III) and also contains the nitrocyanamide anion, NCNNO 2 −. The compound NCNNO 2 − appears to have formed by loss of HN 3 from (II) or N 3 − from (III) during one of the synthesis attempts of Rb(II). The major atom motions in the IR spectra of (I), (II), and (III) were assigned on the basis of density functional theory (DFT) using the B3LYP method. Both the IR spectral and crystal structure trends show that increasing the negative charge on the anion primarily shifts the partial double bond character from the CNNO 2 bond to the CNNO 2 bond.

Ammonium eneselenolates: stereochemistry and electronic properties.

Ammonium eneselenolates were generated with high efficiency by reacting selenothioic acid S-esters with a THF solution of TBAF. The methylation of ammonium eneselenolates gave ketene selenothioacetals as stereoisomeric mixtures. The ratio of the two stereoisomers depended on the duration of the reaction before the addition of MeI. Ammonium eneselenolates were characterized by examining their (1)H, (13)C, and (77)Se NMR spectra, which indicated that ammonium eneselenolates were present almost exclusively as Z-isomers. These results suggested that ammonium eneselenolates are kinetically generated as stereoisomeric mixtures, and isomerization of E-isomers to Z-isomers then takes place to result in the exclusive formation of Z-isomers. During the methylation of Z-isomers of ammonium eneselenolates, the isomerization of Z-isomers to E-isomers occurs to give stereoisomeric mixtures of ketene selenothioacetals. NMR spectra of ammonium eneselenolates implied that the electrons at the selenium atom are somewhat delocalized to the carbon-carbon double bond and the carbon-selenium bond shows partial double-bond character.

Bis(N-methyl-N-phenylthiocarbamoyl) disulfide

In the title mol­ecule, C16H16N2S4, the two di­thio­carbamate groups, which are perpendicular to each other, are linked by an S—S bond. The di­thio­carbamate groups adopt a trans-planar conformation and form a dihedral angle of 89.75 (8)° with each other. The phenyl rings make dihedral angles of 77.3 (2) and 89.2 (2)° with the di­thio­carbamate plane. The C—N bonds in the di­thio­carbamate groups show partial double-bond character.

Molecular structures and vibrations of m-methylaniline in the S 0 and S 1 states studied by laser induced fluorescence spectroscopy and ab initio calculations

The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled m-methylaniline have been obtained for the S 1←S 0 transition, in which some of the bands have been observed for the first time. The main spectral bands have been assigned by comparison with those of other relevant substituted benzenes. It was found that the spectra exhibit an important feature which is the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31G* and CIS/6-31G* show that the optimized structure of m-methylaniline in the ground state is not planar with the amino group having sp 3 hybridation-like character due to the existence of lone-paired electrons on the nitrogen atom. Upon electronic excitation, the CN bond exhibits a partial double bond character, indicating an enhanced interaction between the ring and the NH 2 group as in the case of aniline.

Synthesis and characterization of sulfide, sulfide-sulfonium, and bissulfide derivatives of [B12H12]2-. Additivity of Me2S and MeS- substituent effects in 11B NMR spectra of disubstituted icosahedral boron clusters.

The 1,2-, 1,7-, and 1,12-isomers of (Me2S)2B12H10 (O, M, and P) react with potassium phthalimide in DMF or EtSNa in CH3CN/EtOH upon reflux producing the corresponding isomers of [(MeS)(Me2S)B12H10]- (O1-, M1-, P1-). If excess of either nucleophile is used, [Me2SB12H11]- (1) and O, M, P can be converted into dianions [MeSB12H11]2- (2) and [(MeS)2B12H10]2- (O2-, M2-, P2-). The use of EtSNa is recommended since it facilitates the isolation of products compared to the potassium phthalimide method. When 1 or O, M, P are treated with an excess of an alkali metal (Na, K) in liquid ammonia at -40 degrees C, sulfide 2 or bissulfide dianions O2-, M2-, P2- are obtained cleanly and almost instantly. While both the nucleophilic substitution and alkali metal reduction methods are useful for the synthesis of dianions 2, O2-, M2-, and P2-, only the former method is suitable for the synthesis of the sulfide-sulfonium anions O1-, M1-, P1-. The analysis of the 11B NMR spectra of 1, O, M, P and anions derived from them demonstrated that the spectra of the disubstituted species can be predicted qualitatively, keeping in mind the simple substituent effects obtained from the spectra of monosubstituted anions 1 and 2. Some evidence is found for small partial double bond character of the B-SMe bonds in anions. [MePPh3]+ salts of [MeSB12H11]2- (2) and [1-(MeS)-7-(Me2S)B12H10]- (M1-) are structurally characterized by single-crystal X-ray diffraction analysis. Crystal data: [MePPh3]2[MeSB12H11], P2(1) (No. 4), a = 9.243(1) A, b = 18.272(1) A, c = 12.548(1) A, beta = 103.17(1) degrees, Z = 2; [MePPh3][1-(MeS)-7-(Me2S)B12H10], P1 (No. 2), a = 9.278(2) A, b = 12.003(5) A, c = 14.819(7) A, alpha = 112.18(4) degrees, beta = 105.61(3) degrees, gamma = 92.91(3) degrees, Z = 2.

Laser spectroscopy of jet-cooled ethyl radical: Infrared studies in the CH2 stretch manifold

A glow discharge, slit supersonic expansion in conjunction with direct infrared laser absorption methods has been utilized to record high resolution vibration–rotation spectra of the CH3–CH2 ethyl radical. The slit supersonic expansion results in efficient rotational cooling from discharge temperatures down to Trot≈14 K, permitting unambiguous rotational assignment and spectral analysis for the first time. Furthermore, a discharge on/discharge off data collection scheme permits clean discrimination between spectral contributions from radical vs precursor absorption. Spectra for both symmetric and asymmetric CH2 stretch manifolds are observed. Least-squares fits of transition frequencies out of the K=0 ground state manifold to a near prolate top model Hamiltonian reproduce the data to within the 7 MHz experimental uncertainty and provides rotational constants for both ground and vibrationally excited symmetric/asymmetric CH2 stretch states. The band origins for the CH2 stretch vibrations [3037.018 96(12) cm−1 and 3128.693 69(13) cm−1] are in reasonable agreement with ab initio theory; though predictions for relative intensities of the two bands are off by nearly an order of magnitude and indicate that the transition moment vector is tilted 33° away from each C–H bond toward the C–C bond axis. Structural analysis based on the measured B and C rotational constants imply a C–C bond distance of 1.49 Å. This is consistent with partial (≈15%) double bond character for the ethyl radical carbon frame and in excellent agreement with theoretical predictions.

Synthesis, equilibrium and NMR studies of lanthanide(III) complexes of the N-mono(methylamide) and N ′-mono(methylamide) derivatives of diethylenetriamine-N,N,N ′,N ″,N ″-pentaacetic acid†

Two derivative ligands of diethylenetriamine-N,N,N′,N′′,N′′-pentaacetic acid (H5DTPA; H5L1) were synthesized: the symmetric and asymmetric mono(methylamides) DTPA-N′-MA (H4L3) and DTPA-N-MA (H4L4). The protonation constants (log KiH) of L3 and L4 were obtained by pH-potentiometric titration: 10.04, 8.41, 2.73, 1.94 and 10.18, 6.19, 3.55, 2.0, respectively. The protonation constants and the sites of protonation were interpreted on the basis of the pH dependence of the chemical shifts of the non-labile protons. The stability constants (KLnL) of the complexes of these ligands with lanthanide(III) ions were determined by direct pH-potentiometry and competition titration. The stability constants decrease in the sequence LnL1 > LnL3 > LnL4. The log KLnL values of the complexes LnL3 and LnL4 increase with increasing atomic number of Ln3+ from La to Gd, then remain roughly unchanged up to Er and subsequently decrease slightly to Lu. The 1H and 13C NMR spectra reveal the presence of 2 isomers for the complexes LnL3 and 4 isomers for LnL4 at around 0 °C. The AB multiplets of the acetate methylene protons demonstrate the long lifetime of the Ln3+–N bonds. The coupling observed between the methyl and methylene protons of the methylamide group in the 2-D COSY spectra indicates partial double bond character of the C–NMe bond.

A DFT/Electron Localization Function (ELF) Study of the Bonding of Phosphinidenes with N-Heterocyclic Carbenes

The bonding between model phosphinidene PH and two types of cyclic Arduengo's carbenes, the aromatic C3H4N2 (1) and the related saturated C3H6N2 (2) species, respectively, have been analyzed in terms of the electron localization function (ELF). In a first step, the bare carbenes have been studied, and then, in a second step, the changes brought about by PH complexation have been treated. It has been shown that the bonding mode essentially results from a dative bond formed by the nucleophilic carbenic carbon of the ring and the PH acceptor site. Some back bonding from P creates a partial double-bond character around the C−P unit. The latter character is more pronounced when PH is linked to the saturated carbene 2. A comparison of the ring aromatic properties, in terms of nucleus-independent chemical shifts has been achieved, showing that complexation of 1 by PH diminishes the ring aromaticity through relocalization of the electrons on the N atoms.