The anisotropy of the optical polarizability of naphthalene-d8 in its lowest triplet state (photoselection method)

An equation is given for the evaluation of the anisotropy of the optical polarizability from the induced birefringence produced by photoselection. The anisotropy of the optical polarizability of naphthalene-d₈ in the lowest triplet state is calculated.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

Synthesis and structural characterization of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)C(Ph)], generated via an alkyne-Ti benzyne coupling reaction

The thermolysis of [(C₅H₄)SiMe₂(N-t-Bu)]TiPh₂ in the presence of diphenylacetylene proceeds at 80 °C in cyclohexane solution with the sole formation of the titanacyclic complex [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)], which has been characterized by solution NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti-C bonds of 2.081(7) and 2.103(6) Å in [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)] reflect the increased electrophilicity of the d⁰ Ti(IV) center arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.     

Interaction potential for He-H2 in the region of the van der Waals minimum

Interaction energies for the He-H₂ system have been computed by a VB method for the intermolecular distances 5.2 ? R ? 20.0 bohr and two different orientations of the H₂ molecule (θ = 0°, 90°). The results, especially for the anisotropy, are in good agreement with experiment. The dispersion constants C₆ and C₈ and the corresponding anisotropy constants α₆ and α₈ are presented.     

Electrostatic energies of the {CoNO}8 group in ligand fields

The qualitative features of the electronic states of the {CoNO}⁸ group are investigated by calculating the electrostatic energies of the (d _z2, d _xz, d _yz)², (d _xz, d _yz)², and (d _z2)² electron configurations in D′₄ symmetry. The geometries of the {CoNO}⁸ group are correlated with the behavior of the singlet electronic states in the D′₄ ligand field.     

Cyclopalladation of 3-methoxyimino-2-phenyl-3H-indoles

The direct cyclopalladation of 3-methoxyimino-2-(4-chlorophenyl)-3H-indole (1a) and 3-methoxyimino-2-phenyl-3H-indole (1b) results in the regioselective activation of the ortho σ[C(sp², phenyl)-H] bond affording (μ-OAc)₂[Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}]₂ (2) {R = Cl (2a) or H (2b)} that contain a central “Pd(μ-OAc)₂Pd” core. Compounds 2a and 2b reacted with triphenylphosphine (in a molar ratio PPh₃:2 = 2) giving [Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}(OAc)(PPh₃)] (3) {R = Cl (3a) or H (3b)}. Treatment of 2a or 2b with a slight excess of LiCl in acetone produced the metathesis of the bridging ligands and the formation of (μ-Cl)₂[Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}]₂ (4) {R = Cl (4a) or H (4b)} with a central “Pd(μ-Cl)₂Pd” moiety. The reactions of 4a or 4b with deuterated pyridine (py-d₅) or triphenylphosphine gave the monomeric derivatives [Pd{κ²-C,N-C₆H₃-4R-1-(C₈H₄N-3′-NOMe)}Cl(L)] with R = Cl or H and L = py-d₅ (5) or PPh₃ (6). The crystal structure of 6b·1/2CH₂Cl₂ confirmed the mode of binding of the ligand, the nature of the metallated carbon atom and a trans-arrangement of the phosphine ligand and the heterocyclic nitrogen. Theoretical calculations on the free ligands are also reported and have allowed the rationalization of the regioselectivity of the cyclopalladation process.     

Effects of chemical shift anisotropy and 14N coupling on the 1H and 195Pt nuclear magnetic resonance spectra of platinum complexes

Broadening of the ¹⁹⁵Pt satellites in the ¹H NMR spectrum of trans-Pt(ethene)(2-carboxy-pyridine)Cl₂ at high field arises from relaxation of ¹⁹⁵Pt via the chemical shift anisotropy mechanism. We also demonstrate that well-resolved ¹⁴N-¹⁹⁵Pt couplings can be observed in ¹⁹⁵Pt NMR spectra of Pt(II) and Pt(IV) amine complexes, including anti-tumour agents, at elevated temperature where scalar coupling contributions to ¹⁹⁵Pt relaxation are much reduced.     

A novel method for the formation of N-glycosides using hydroxamate

Direct formation of Asn-linked carbohydrate by N-glycosylation has been difficult, because of the lack of nucleophilicity of carboxamide nitrogen. We report here the novel N-glycosylation using Asn hydroxamate as a glycosyl acceptor. Reaction with glycosyl fluoride or glycosyl trichloroacetimidate afforded N-glycoside and subsequent reduction with SmI₂ gave Asn-linked glucose. Carbamate derived hydroxamates proved to have even enhanced reactivity to give N-glycosides in high yields.     

Biocatalytic and chemical routes to all the stereoisomers of methionine and ethionine sulfoxides

Biotransformations of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine by Beauveria bassiana ATCC 7159 or Beauveria caledonica ATCC 64970 produce the corresponding (S_S) sulfoxides in good yield and diastereomeric excess. Pure (S_SS_C) diastereomers can be obtained from l-series substrates by crystallisation of the biotransformation extract, and the corresponding (S_SR_C) products obtained from d-series substrates by chromatography of the biotransformation extract. Hydrogen peroxide-catalysed oxidation of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine gives diastereomeric mixtures from which the (S_SS_C) and (R_SR_C) diastereomers can be obtained by crystallisation, and the (S_SR_C) and (R_SS_C) diastereomers obtained by chromatography. N-Cbz- and N-t-Boc methionines are also converted to sulfoxides with predominant (S_S) configuration by both B. bassiana and B. caledonica, but the isolated yields and d.e. of products were generally lower than those obtained from the N-phthaloyl substrates.Removal of the N-phthaloyl group from diastereomerically pure methionine and ethionine sulfoxides gave the corresponding amino acid sulfoxides in high yield; removal of N-Cbz and N-t-Boc groups from protected methionine sulfoxides was also achieved without loss of configuration at sulfur.     

External photocatalyst-free C-H alkylation of N-sulfonyl ketimines with alkanes under visible light

A simple, practical and eco-friendly visible light-induced alkylation of N-sulfonyl ketamine under metal-, additive-, external photocatalyst-free conditions was developed. This photocatalytic method utilized low cost and abundant alkanes as the atom economy alkyl sources with H₂O₂ as the environmentally beneficial oxidant, allowing for the efficient construction of diverse valuable 4-alkylated sulfonyl ketamines. The N-sulfonyl ketamine played a dual role of reactant and photocatalyst, thus simplifying the reaction system.     

Magnetic properties of mixed uranium and 3d element chalcogenides of the MU8X17 type

Magnetic susceptibility measurements in the temperature range 4.2–300°K for the MU₈X₁₇ type chalcogenides, where M is a 3d transition metal or Mg, and X = S or Se, were carried out. For comparison, the magnetic properties of UTe₂ are also given. Almost all the mixed uranium and 3d-transition element chalcogenides are induced-antiferromagnets, as indicated from the occurrence of the susceptibility maxima on the χ vs. T curves and large negative values of the paramagnetic Curie temperatures. The influence of the 3d-transition metals on setting up the magnetic order in the MU₈X₁₇-type compounds is discussed.     

NMR (1H, 13C, 29Si) study of some allylhalogenosilanes

¹H, ¹³C and ²⁹Si NMR spectra of the allylchlorosilanes (CH₂CH-CH₂-)_xSiCl_4?x and of triallylbromosilane have been analysed. Results are discussed in terms of inductive and steric effects and of contributions of diamagnetic anisotropy. There is no conclusive evidence for (p-d)π conjugation.     

Synthesis and Structure of Nido-Carboranyl Azide and Its “Click” Reactions

Novel zwitter-ionic nido-carboranyl azide 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was prepared by the reaction of 9-Cl(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with NaN₃. The solid-state molecular structure of nido-carboranyl azide was determined by single-crystal X-ray diffraction. 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was used for the copper(I)-catalyzed azide-alkyne cycloaddition with phenylacetylene, alkynyl-3β-cholesterol and cobalt/iron bis(dicarbollide) terminal alkynes to form the target 1,2,3-triazoles. The nido-carborane-cholesterol conjugate 9-3β-Chol-O(CH₂)C-CH-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with charge-compensated group in a linker can be used as a precursor for preparation of liposomes for Boron Neutron Capture Therapy (BNCT). A series of novel zwitter-ionic boron-enriched cluster compounds bearing a 1,2,3-triazol-metallacarborane-carborane conjugated system was synthesized. Prepared conjugates contain a large amount of boron atom in the biomolecule and potentially can be used for BNCT.     

Experimental and theoretical study of the hyperfine structure in the (5d+6s)96p configurations of Pt I

The hyperfine structure of the odd configurations 5d ⁹6p and 5d ⁸6s6p was studied with laser optogalvanic spectroscopy and high resolution interferometry in a platinum hollow cathode. A parametric hyperfine structure analysis for the configurations (5d+6s)⁹6p with 10 excited odd-parity levels was performed for¹⁹⁵Pt. We obtained one-electron hfs parameters,a _5d ⁰¹ =1160(320) MHz,a _6s ¹⁰ =35600(5300) MHz anda _6p ⁰¹ =1300(780) MHz for the configuration 5d ⁸6s6p. The corresponding $\left\langle {r^{ - 3} } \right\rangle _{nl}^{k_s k_l } $ values are compared with those known for other 5d-elements.     

Raman study of reorientational motion of liquid benzene

Raman spectra of the 943 cm^?1 band of liquid benzene-d₆ were measured at temperatures up to 120°C and at pressures up to 4000 bar. Rotational diffusion constants for tumbling and spinning motions were obtained from Raman band widths and NMR T₁ data. Experimental results were compared with theoretical diffusion constants computed on the basis of various models. It is found that the Hynes—Kapral—Weinberg theory gives the best prediction for the temperature and pressure dependence of the diffusion constants and for the rotational anisotropy in liquid benzene.     

Synthesis of Zwitter-Ionic Conjugate of Nido-Carborane with Cholesterol

9-HC≡CCH₂Me₂N-nido-7,8-C₂B₉H₁₁, a previously described carboranyl terminal alkyne, was used for the copper(I)-catalyzed azide-alkyne cycloaddition with azido-3β-cholesterol to form a novel zwitter-ionic conjugate of nido-carborane with cholesterol, bearing a 1,2,3-triazol fragment. The conjugate of nido-carborane with cholesterol, containing a charge-compensated group in the linker, can be used as a precursor for the preparation of liposomes for BNCT (Boron Neutron Capture Therapy). The solid-state molecular structure of a nido-carborane derivative with the 9-Me₂N(CH₂)₂Me₂N-nido-7,8-C₂B₉H₁₁ terminal dimethylamino group was determined by single-crystal X-ray diffraction.     

Infrared and Raman spectra of the trimethylsilyl ester of the cubic octameric silicate, (Si8O20)[Si(CH3)3]8, at very high pressures

Infrared and FT-Raman spectra have been recorded, at ambient temperature, for the solid trimethylsilyl ester of the cubic octameric silicate, (Si₈O₂₀)[SiCH₃)₃]₈ (Q₈M₈), at various pressures up to ∼50 kbar with the aid of a diamond-anvil cell. The vibrational spectroscopic data indicate that there is pressure-induced structural change occurring at ∼20 kbar. Moreover, the central Si₈O₂₀ framework (D_4h symmetry) is remarkably resistant to applied pressure, as are other high-symmetry systems (e.g., C₆₀, I_h symmetry), while the trimethylsilyl side-chains are more easily compressed. The pressure sensitivity (dν/dp), 1.35 cm⁻¹/kbar, of the ν(C–H) mode of the trimethylsilyl groups in the low-pressure phase is by far the greatest.     

Preparation and properties of the formamidino complexes [M(π-C5H5){HC(NR)2}(CO)2] (M = molybdenum or tungsten; R = aryl or alkyl)

The preparation and properties of the complexes [M(π-C₅H₅){HC(NR)₂}CO)₂] (M = Mo, W; R = aryl or alkyl) are reported. The complex [Mo(π-C₅H₅){HC(N-p-tolyl)₂}(CO)₂] could be prepared by (a) reaction of MoCp(CO)₃Cl with M′{HC(N-p-tolyl)₂} (M′ = K, Ag or Cu); (b) irradiation of MoCp(CO)₃Cl with HC(HN-p-tolyl)N-p-tolyl); and (c) reaction of [MoCp(CO)₃]₂ with M′{HC(N-p-tolyl)₂} (M′ = Ag or Cu). The several routes to this complex give indications of the mechanisms of formation. The structure of these complexes and the bonding nature of the metal with the formamidino group is discussed on basis of the ¹H and ¹³C NMR and IR spectra.Reaction of N,N′-dimethyl formamidine with MCp(CO)₃Cl gave the complex [M(π-C₅H₅){HC(NMe)N(CO)Me}(CO)₂], containing a carbonyl inserted between the metal and the formamidino group. Irradiation of this carbamoyl complex caused decarbonylation, yielding the complex [M(π-C₅H₅){HC(NMe)₂}CO)₂].     

Theoretical study on the structures,force field,and vibrational spectra of cyclooctatetraene and cyclooctatetraene-d8

The structures and force field of 1,3,5,7-cyclooctatetraene (COT) have been studied using ab initio theory at the SCF level with the 4-21G basis set. The quadratic force field of the D_2d structure obtained by systematic scaling of the ab initio force constants successfully reproduces the observed frequencies of COT and COT-d₈ with a mean deviation of less than 10 cm⁻¹ for non-CH stretching modes. On the basis of the calculated results, assignments of the fundamental vibrations are examined. The normal mode υ₅ is reassigned to a weak band at 758 cm⁻¹ in the Raman spectrum of COT and to a weak band at 591 cm⁻¹ in the Raman spectrum of COT-d₈. The calculations favor the assignment of υ₂₆ given by Lippincott et al. [J. Am. Chem. Soc. 73, 3370 (1951)] over the revised assignment of Perec [Spectrochim. Acta 47A, 799 (1991)]. The calculations also furnish reliable prediction for the inactive A₂ fundamentals of COT and COT-d₈. The fundamental frequencies and IR and Raman intensities of ¹³CC₇H₈, which constitutes about 9% of COT in natural abundance, are also calculated. Only ν₁₀ (calculated at 908 cm⁻¹) of the formal inactive A₂ modes has appreciable Raman intensity (0.23 Å⁴/amu). A spectral feature due to this fundametal is identified in the liquid Raman spectrum of Tabacik and Blaise [C. R. Acad. Sci. Ser. II 303, 539 (1986)] as a weak peak at 908 cm⁻¹.     

J and term dependences in the isotope shift of Eu I

High-resolution laser atomic beam spectroscopy has been applied to studyJ and term dependences in the isotope shift of the levels 4f ⁷5d6s a ¹⁰ D _J ,a ⁸ D _J of Eu I. A parametric analysis of the isotope shift has been performed. TheJ dependence is interpreted through two term-dependent parametersz _5d , and the term dependence through one parameterΔT:z _5d (a ¹⁰ D)=44.1 (2.6) MHz,z _5d (a ⁸ D)=55.9 (2.3) MHz,ΔT=408.5 (3.2) MHz. Ab initio Hartree-Fock and Dirac-Fock calculations have been made to interpret these parameters. Within the accuracy of the calculations the parameters can be attributed to field shift effects.