Ion‐Pairing of Phosphonium Salts in Solution: C?H⋅⋅⋅Halogen and C?H⋅⋅⋅π Hydrogen Bonds

The ¹H NMR chemical shifts of the C(α)? H protons of arylmethyl triphenylphosphonium ions in CD₂Cl₂ solution strongly depend on the counteranions X^?. The values for the benzhydryl derivatives Ph₂CH? PPh₃⁺ X^?, for example, range from δ_H=8.25 (X^?=Cl^?) over 6.23 (X^?=BF₄^?) to 5.72 ppm (X^?=BPh₄^?). Similar, albeit weaker, counterion‐induced shifts are observed for the ortho‐protons of all aryl groups. Concentration‐dependent NMR studies show that the large shifts result from the deshielding of the protons by the anions, which decreases in the order Cl^? > Br^? ? BF₄^? > SbF₆^?. For the less bulky derivatives PhCH₂? PPh₃⁺ X^?, we also find C? H???Ph interactions between C(α)? H and a phenyl group of the BPh₄^? anion, which result in upfield NMR chemical shifts of the C(α)? H protons. These interactions could also be observed in crystals of (p‐CF₃‐C₆H₄)CH₂? PPh₃⁺ BPh₄^?. However, the dominant effects causing the counterion‐induced shifts in the NMR spectra are the C? H???X^? hydrogen bonds between the phosphonium ion and anions, in particular Cl^? or Br^?. This observation contradicts earlier interpretations which assigned these shifts predominantly to the ring current of the BPh₄^? anions. The concentration dependence of the ¹H NMR chemical shifts allowed us to determine the dissociation constants of the phosphonium salts in CD₂Cl₂ solution. The cation–anion interactions increase with the acidity of the C(α)? H protons and the basicity of the anion. The existence of C? H???X^? hydrogen bonds between the cations and anions is confirmed by quantum chemical calculations of the ion pair structures, as well as by X‐ray analyses of the crystals. The IR spectra of the Cl^? and Br^? salts in CD₂Cl₂ solution show strong red‐shifts of the C? H stretch bands. The C? H stretch bands of the tetrafluoroborate salt PhCH₂? PPh₃⁺ BF₄^? in CD₂Cl₂, however, show a blue‐shift compared to the corresponding BPh₄^? salt.     

Applications of 95Mo NMR. 5—substituent effects in the 95Mo and 13C NMR spectra of benzyltricarbonyl(η5-cyclopentadienyl)molybdenum(II) derivatives

A systematic study has been made of the effects of substituent induced chemical shifts in [(η⁵-C₅H₅)(CO)₃Mo(CH₂C₆H₄R)] compounds. Both ⁹⁵Mo and ¹³C NMR shifts in the aromatic ring are reported. The (η⁵-C₅H₅)(CO)₃MoCH₂? group is a reasonably strong resonance donor (σ_R° = ?0.21) and weak inductive donor (σ_I = ?0.07). The molybdenum chemical shifts are extremely sensitive to the effects of distant substituents (range c. 40 ppm). Since the shift correlates well with substituent constants in this series, it is suggested that the chemical shift is controlled by the paramagnetic term for this spin 5/2 nucleus.     

29Si NMR spectra of trimethylsilylated cyclic acyloins and ketones. 29Si chemical shifts as a measure of ring size

²⁹Si chemical shifts are reported for nine 1,2-bis(trimethylsiloxy)cycloalkenes and four 1-trimethylsiloxycycloalkenes, (Me₃SiO)_xC_nH_2n–2–x (x=1, 2). For cycloalkene derivatives with n?8 the silicon shift exhibits a strong dependence on the ring size, although the silicon is exocyclic and is separated by two bonds from the olefinic carbon atom. The dependence can be exploited for ring size determination of cyclic ketones after trimethylsilylation.     

Proton and boron-11 magnetic resonance studies of some potassium tetraarylborates

Proton and boron-11 magnetic resonance spectra for several potassium para-substituted tetraarylborate compounds [KB(C₆H₄-pX)₄, where X is H, OCH₃, CH₃, Br, Cl, F, CF₃] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para-substituent. Additionally, the boron-11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para-substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions.     

Electronic mechanism in cadmium chemical shift

Cadmium chemical shifts are studied theoretically by the ab initio molecular orbital method. The compounds studied are CdMe₂, CdMeEt, CdEt₂, CdMe(OMe), Cd(OMe)₂, CdMe(SMe) and Cd(SMe)₂. The calculated values of the Cd chemical shifts agree excellently with the experimental values, showing quantitative reliability of the theoretical method used in this paper. The cadmium chemical shift is mainly due to the p mechanism in the paramagnetic term. The contribution of the d mechanism is small. Therefore, the metal chemical shift is proportional to the π-electron donating ability of the ligands. The diamagnetic contribution, which is determined solely by a structural factor, is small for the chemical shift. The difference between the methyl and ethyl ligands is attributed partly to the p mechanism (paramagnetic) and partly to the structural factor (diamagnetic). The outer d orbitals of the sulfur in the SMe ligand are unimportant for the Cd chemical shift.     

Struktur-Reaktivitätsuntersuchungen mit heterosubstituierten Nitrilen—VII: 13C-, 14N- und 19F-NMR-Spektroskopische Untersuchungen an Verbindungen vom Typ Ar?X?CN

The chemical shifts of aromatic nitriles of the general structure para-Y? C₆H₄? X? CN with X = O, S, Se and N(CH₃) have been investigated by the ¹³C NMR technique. For cyanates (X = O) the ¹⁴N shifts and for Y = F the ¹⁹F shifts were likewise measured. The chemical shifts and the corresponding ¹³C shift increments Δ_n have been found to correlate with the appropriate substituent constants σ_R⁰, σ_p⁰ and σ_I, as well as with the π-electron densities calculated in the PPP approximation.     

Coordination diversity in tin compounds with bis(benzoxazole)phenol as a polydentate ligand: Synthesis and crystal structure studies

Abstract

The reaction of 2,6-bis(benzoxazolyl)-4-tert-butylphenol (HL) with [ⁿBu_xSnCl_4?x] (x?=?0, 1) in 1:1 stoichiometry yielded the tin coordination complexes [(HL)SnⁿBu_xCl_4?x] [x?=?0 (1); x?=?1 (2)]. Deprotonation of HL was performed using reagents having groups with high basicity such as ⁿBuLi or [Sn{N(SiMe₃)₂}₂]. These basic reagents prompted the coordination of the ligand in its anionic form, yielding the complexes [(thf)₂Li(L)SnCl₄] (3) and [(L)Sn{N(SiMe₃)₂}] (4), respectively. The molecular structure of HL displayed an intramolecular hydrogen bond OH—N and a planar arrangement of the bis(benzoxazolyl)phenolic system. In the molecular structures of both complexes containing HL an intramolecular hydrogen bond of NH—O type was also present. The coordination of the ligand in either neutral or anionic form is described by a κO,κN chelate mode toward Sn. All complexes displayed bis(benzoxazolyl)phenolic moieties close to planar; the least planar system was observed in 4 that was also studied by DFT methods.     

Discrete Neutral Niobium Cluster Units in Compounds of the Type [Nb6Cl14L4] with L = O or N Donor Ligand

Six new hexanuclear niobium cluster compounds of the general formula [Nb₆Cl₁₄L₄] · x(solvent molecule) [L = neutral O or N donor ligand, x = 0–2.5; pyrimidine ( 1 ), 1‐methyl imidazole ( 2 ), isobutyronitrile ( 3 ), isopropyl alcohol ( 4 ), triphenylphosphine oxide ( 5 ), dimethyl sulfoxide ( 6 )] were prepared. The syntheses were carried out by dehydration of the precursor [Nb₆Cl₁₄(H₂O)₄] · 4H₂O with different water scavangers, like acetic anhydride, trimethyl acetic anhydride and diethylcarbonate in the presence of the corresponding neutral ligand. The structures are determined by single‐crystal X‐ray diffraction. The specific bonding situations of the ligands to the [Nb₆Cl₁₂]²⁺ cluster cores are compared and discussed. The phenomenon of the observed M₆ distortion is explained and interpreted based on the matrix effect and the terminal ligand effect. In addition, other interactions between the cluster units, such as hydrogen bonding and π–π stacking are discussed.     

1H-NMR Spectroscopy of Gold Drugs. High-Resolution Studies of β-D-Thioglucosetetraacetate Phosphine Complexes of Au(I)

¹H-NMR data (11.74 Tesla) for the gold(I) complexes [R₃P-Au-(2,3,4, 6-tetra-O-acetyl-1-thio-β-D -glucopyranosido-S)] (R = Et, Cyclohexyl, C₆H₅, p-CH₃OC₆H₄) with sulfur coordination to gold, are reported. The resonances associated with the sugar protons have been assigned although these have similar chemical environments. The coordination chemical shifts, Δδ, for the Au? S? C? H proton are ≈? 0.6 ppm, and support S-coordination to gold.     

Carbon-13 nuclear magnetic resonance studies of anthraquinones. Part III—correlation of substituent effects for 2-substituted anthraquinones

The ¹³C chemical shifts of 2-substituted and 2,6-disubstituted anthraquinones have been determined and assigned. The C-1, 2, 3, 4, 13 and C-14 chemical shifts of 2-substituted anthraquinones are correlated with the chemical shifts of monosubstituted benzenes. A three-parameter correlation with Swain and Lupton's ? and ? parameters and Schaefer's Q parameter provides relationships for the prediction of all chemical shifts of 2-substituted anthraquinones from the substituent parameters. Q values for the SCH₃, OCOCH₃, C₂H₅ and C(CH₃)₃ groups are proposed. The two types of correlations are compared for predicting chemical shifts.     

Controlled Redox Chemistry at Cerium within a Tripodal Nitroxide Ligand Framework

Ligand reorganization has been shown to have a profound effect on the outcome of cerium redox chemistry. Through the use of a tethered, tripodal, trianionic nitroxide ligand, [((2‐tBuNOH)C₆H₄CH₂)₃N]^3? (TriNO_x^3?), controlled redox chemistry at cerium was accomplished, and typically reactive complexes of tetravalent cerium were isolated. These included rare cationic complexes [Ce(TriNO_x)thf][BAr^F₄], in which Ar^F=3,5‐(CF₃)₂‐C₆H₃, and [Ce(TriNO_x)py][OTf]. A rare complete Ce–halide series, Ce(TriNO_x)X, in which X=F^?, Cl^?, Br^?, I^?, was also synthesized. The solution chemistry of these complexes was explored through detailed solution‐phase electrochemistry and ¹H NMR experiments and showed a unique shift in the ratio of species with inner‐ and outer‐sphere anions with size of the anionic X^? group. DFT calculations on the series of calculations corroborated the experimental findings.     

Solid‐state CP/MAS 13C NMR studies on conformational polymorphism in sertraline hydrochloride,an antidepressant drug

The C(2) isotropic chemical shift values in solid‐state CP/MAS ¹³C NMR spectra of conformational polymorphs Form I (δ 28.5) and III (δ 22.9) of (1S,4S)‐sertraline HCl ( 1 ) were correlated with a γ‐gauche effect resulting from the respective 162.6° antiperiplanar and 68.8° (+)‐synclinal C(2)? C(1)? N? CH₃ torsion angles as measured by X‐ray crystallography. The similarity of the solution‐state C(2) chemical shifts in CD₂Cl₂ (δ 22.8) and DMSO‐d₆ (δ 23.4) with that for Form III (and other polymorphs having C(2)? C(1)? N? CH₃ (+)‐synclinal angles) strongly suggests that a conformational bias about the C(1)? N bond exists for 1 in both solvents. This conclusion is supported by density functional theory B3LYP/6‐31G(d)‐calculated relative energies of C(1)? N rotameric models: (kcal) 0.00 [73.8 °C(2)? C(1)? N? CH₃ torsion angle], 0.88 (168.7°), and 2.40 (?63.4°). A Boltzmann distribution of these conformations at 25 °C is estimated to be respectively (%) 80.3, 18.3, and 1.4. Copyright © 2002 John Wiley & Sons, Ltd.     

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

All carbon-13 chemical shifts for 11 para-substituted N,N-dimethylbenzamides in 1 mole % chloroform solution are reported, with assignments based upon double resonance experiments, analogy to chemical shifts of benzamide, and self-consistency between experimental and calculated values using recognized substituent parameters. In contrast to earlier reports, the aryl carbon chemical shift assignments for N,N-dimethylbenzamide are C-2, 127.0; C-3, 128.7; C-4, 129.4, and for p-chloro-N,N-dimethylbenzamide are C-1, 134.6; C-4, 135.5 ppm, relative to internal TMS. Good Hammett correlations (σ_p) are reported for ¹³C chemical shifts of C-1 (σ = 11.9 ppm) and even for the carbonyl group (σ = ?2.3 ppm) but are markedly improved if correlated with σ_p+ (σ = 9.5 ppm) and Dewar's F (σ = ?1.9 ppm), respectively. Excellent Swain–Lupton F and R correlations were found for some of the ¹³C chemical shifts and yielded values for percent resonance contributions to transmission of substituent effects as follows, C-1, 75 ± 4%; C-2, 51 ± 3%; C?O, 31±2%. These are compared to similar values calculated from the C?O of benzoic acids of 34±10%, and from the nitrogen-15 chemical shifts of benzamides of 56±2%. Correlations of these ¹³C δ values and ¹⁵N δ values with rotation barriers (ΔG) for N,N-dimethylbenzamides were examined, and it was found that while C?O δ values correlated only poorly the C-1 δ values correlated very well, but the best correlation was for ¹⁵N δ values of benzamides. It is suggested that Δ G and δ ¹⁵N are intrinsically related due to their numerical correlation, and the close similarity in percent resonance contribution of substituent influence on these parameters.     

Studies of bimetallic carboxylates: their synthesis, characterization, biological activity and X-ray structure

Ten novel diorganotin dicarboxylates containing germanium in the carboxylate ligand have been synthesized and their structures have been characterized by IR, Mössbauer and multinuclear NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopies and X-ray diffraction. Also, the twodiastereotopic protons of the methylene group which are directly attached to the chiral center in these compounds have been successfully analyzed for the first time. The resulted ABX system gives three coupling constants and three chemical shifts. The single crystal X-ray analysis of precursor (p-CH₃C₆H₄)₃GeCH(p-CH₃C₆H₄)CH₂COOH revealed the dimeric structure of the molecule through H-bonding between carboxylic acid groups in a conventional manner. The results of their biological activity suggest that the materials have potential to be used as drugs.     

IR laser‐induced synthesis of nanostructured gemanium telluride in the gas phase

The gas‐phase synthesis and chemical vapour deposition of nanostructured germanium telluride has been achieved for the first time. The pulsed IR laser irradiation of gaseous CH₃)₄Ge? (CH₃)₂Te? SF₆ mixtures results in homogeneous decomposition of both organometallics and formation of GeTe_x (x = 1, 2). The amorphous GeTe₂ and crystalline GeTe were identified by Raman and X‐ray photoelectron spectroscopy and by electron diffraction. Their formation is explained by an intermediacy of germanium and tellurium clusters and by reaction between these clusters in a hot laser‐induced zone. Copyright © 2005 John Wiley & Sons, Ltd.     

Palladium(II) and Platinum(II) Complexes of N-Phenyl- and N-Ethyl-N′-pyrimidin-2-ylthiourea

Palladium(II) and platinum(II) complexes of N-ethyl-N′-pyrimidin-2-ylthiourea(HL¹) and N-phenyl-N′-pyrimidin-2-ylthiourea (HL²) have been prepared, and the complexes [M(HL)Cl₂], [Pt(L)₂], [Pd(HL¹)₂]Cl₂, and [Pd(L²)₂] (where M = Pd^II or Pt^II) were characterized. The spectroscopic data are consistent with coordination of thioureas as neutral or monoanionic ligands to Pd^II and Pt^II through S and a pyrimidine-N. The IR spectra show shifts of CS and pyrimidine ring stretch bands to lower and higher frequencies, respectively. The ¹H NMR spectra differentiate between H(4′) and H(6′) resonances and indicate downfield shifts for all protons of pyrimidine [H(4′), H(5′), and H(6′)], two resonances for two N?H protons for complexes containing the neutral ligand (HL), and only one N?H proton chemical shift for complexes containing the monoanion (L). ¹³C NMR chemical shifts of pyrimidine carbons are correlated with the type of bonding between Pd^II or Pt^II and pyrimidine-N. The magnetic susceptibilities suggest a diamagnetic planar structure for all complexes.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Selective One-Pot Syntheses of Mixed Silicon-Germanium Heteroadamantane Clusters

Si_xGe_y alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the Si_xGe_y heteroadamantanes [0] , [1] , and [2] through selective one-pot syntheses starting from Me₂GeCl₂, Si₂Cl₆, and [nBu₄N]Cl. Compound [0] contains six GeMe₂ and four SiSiCl₃ vertices, whereas one and two of the GeMe₂ groups are replaced by SiCl₂ moieties in compounds [1] and [2] , respectively. Chloride-ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism.     

Computational investigation of solvent effect on the structure,spectroscopic properties (13C, 1H NMR and IR,UV), NLO properties and HOMO–LUMO analysis of Ru(NHC)2Cl2(=CH-p-C6H5) complex

This paper presents, a theoretical study of the structural, ¹³C and ¹H NMR chemical shifts, electronic transitions, vibrational analysis, and first hyperpolarizability for Ru(NHC)₂Cl₂(=CH-p-C₆H₅) complex in gas phase and different solvents. The solvent effect on structural parameters, frontier orbital energies, Ru=C_carbene and C_carbene-H stretching frequencies, and chemical shifts of C_carbene, C_NHC and H_carbene of complex was explored based on Polarizable Continuum Model (PCM). The wavenumbers of υ(Ru=C_carbene) and υ(C_carbene-H) of complex in different solvents were correlated with the Kirkwood–Bauer–Magat equation (KBM). As well as, the polarizability and the first order hyperpolarizability values of the investigated compound were computed in various solvents.     

Binuclear copper(II) and oxovanadium(IV) complexes with 2,6-diformyl-4- tert -butylphenol- bis -(1′-phthalazinylhydrazone). Synthesis,properties and quantum chemical study

Four binuclear transition metal complexes: [Cu₂L(μ-OCH₃)]?·?CH₃OH, [Cu₂H₂L(μ-Cl)Cl₂]?·?(CH₃OH), [Cu₂H₂L(μ-Br)Br₂]?·?(CH₃OH), [(VO)₂H₂L(μ-Cl)]Cl₂?·?(CH₃OH) were synthesized by reaction of the Robson-type binucleating ligand H₃L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl₂, CuBr₂ and VOCl₂, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L^?3 is observed in reaction with copper(II) acetate, while monodeprotonated form H₂L^? is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are ?700, ?73, ?50 and ?190?cm^?1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values ?570, ?62, ?53 and ?214?cm^?1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.