The crystal structure of tetrakis[trimethylthiomethyl-platinum(IV)], [Pt(CH3)3(SCH3)4

The crystal structure of trimethyl(thiomethyl)platmum(IV), [Pt(CH₃)₃(SCH₃)]₄, has been determined using X-ray diffraction. The compound has three independent but isostructural tetrameric units in the asymmetric unit. The four metal atoms in each tetramer are linked by bridging thiomethyl sulphurs, with three methyl groups completing the octahedral coordination around each platinum. Mean interatomic distances within the tetramer are PtS, 2.48(2), PtC, 2.00(4), PtPt, 3.80(2) Å, with a mean bridge angle SPtS, 79.1(7)°.     

Hydrolysis of substituted 8-acetoxyquinolines

In the absence of metal ions, the hydrolysis of 2-methyl-8-acetoxyquinoline and of 5-chloro-8-acetoxyquinoline follow the same reaction paths as those of the parent ester 8-acetoxyquinoline, including an intramolecular catalysis by the quinoline nitrogen. Unlike the hydrolysis of the other esters, that of the 2-methyl compound appears not to be catalysed by metal ions, and this is consistent with the view that catalysis by a metal ion involves the formation of a 7-membered chelate structure.     

Anil-Synthese. 19. Mitteilung. Über die Herstellung von Stilbenyl-Derivaten des Isoxazols

Preparation of Stilbenyl Derivatives of Isoxazoles Schiff's bases derived from 3- and 5-(p-formylphenyl)-phenylisoxazoles and o- or p-chloroaniline are reacted with various p-tolyl substituted aromatic heterocycles in the presence of dimethylformamide and potassium hydroxide or potassium t-but-oxide to yield the corresponding heterocyclic substituted stilbenes (‘Anil synthesis’). 5-[4-(Chlorphenylimino-methyl)phenyl]-phenylisoxazoles react less readily than the corresponding 3-isomers.     

Photoactivated tungsten hexacarbonyl-catalyzed conversion of alkynols to glycals

The photoactivated W(CO)(6)/DABCO/THF system has been used for the formal endo-cyclization of alkynes to pyran rings. We found that the regioselectivity of ring closure depends on the relative configuration of the 3,5-dihydroxy-1-alkynes, as well as, more decisively, on the type of O-protective group. Oxygen substitution at the propargylic carbon slows the rate of alkyne insertion and allows for dihydrofuran formation through exo-cyclization. In contrast, the use of bulky silyl ethers or carbon substituents leads to dihydropyrans through endo-cyclization. Substrates bearing leaving groups such as esters, phenols, or thiophenols at the propargylic site eliminate and thus represent a limitation to the cycloisomerization methodology. Propargyl vinyl ethers will rearrange to give dienals instead of glycals. 1,2-Wittig rearrangement products of dihydropyrans are readily prepared and converted to complex bicyclic building blocks for organic synthesis.     

Low-coordinate chromium siloxides: the "box" [Cr(mu-Cl)(mu-OSitBu3)]4, distorted trigonal [(tBu3SiO)3Cr][Na(benzene)] and [(tBu3SiO)3Cr][Na(dibenzo-18-c-6)], and trigonal (tBu3SiO)3Cr

Treatment of CrCl(2)(THF)(2) with NaOSi(t)Bu(3) afforded the tetrameric "box" [Cr(mu-Cl)(mu-OSi(t)Bu(3))](4) (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)(2) (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl(2)Cr(4-pic)(2) and trans-(silox)(2)Cr(4-pic)(x) (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(mu-Cl)(mu-OH)](4) (1') revealed that its singly occupied 3d orbitals spanned an energy range of approximately 2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na.C(6)H(6) (4, Y shaped, angle OCrO(Na) = 91.28(7) degrees), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)(3)Cr][Na(dibenzo-18-crown-6)] (5, angle OCrO = approximately 120 degrees, (120 + alpha) degrees, (120 - alpha) degrees). Calculations of [((t)Bu(3)SiO)Cr(mu-OSi(t)Bu(3))(2)]Na (4') and Cr(silox)(3)(-) (5') provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)(3)Cr (6) was synthesized from CrCl(3)(THF)(3) for structural and calculational comparisons to the chromous derivatives.     

An SCF-MS-Xα study of the bonding and nuclear quadrupole coupling in diatomic halogens and interhalogens in the ground X Σ and B Π 0 excited states

SCF-MS-Xα calculations of the electronic structure of diatomic halogens and interhalogens XY (X = I, Br, Cl; Y = I, Br, Cl, F) have been used to investigate the bonding and nuclear quadrupole coupling in these molecules. Calculations have been carried out for the ground X ¹ Σ electronic state, and for the excited B ³ Π₀ state in the case of I₂, Br₂, ICl and IBr. Good agreement (to within 10% in most cases) is obtained between the calculated and observed nuclear quadrupole coupling constants for the molecules in the ground state. For the excited state the agreement is not as good, but the calculation does reproduce the observed decrease in the coupling constants to less than one quarter of their ground state values, and analysis of the contributions to the field gradients clearly shows the reasons for this. The electric dipole moments and electric quadrupole moments of the molecules have also been calculated. However, these prove to be much more strongly dependent on the variables used in the calculation (atomic sphere radii, inclusion of d orbitals). The results of the calculations have also been used to test some of the assumptions made in the Townes and Dailey method of analysis of nuclear quadrupole coupling data.     

Reduction of nitroaromatics to arylnitrenium ions by vinyl halide cations

The title reduction of nitroaromatics ArNO(2) by vinyl halide radical cations CH(2)[double bond]CH-X(+*)(X = Cl or Br) to form arylnitrenium ions ArNH(+) involves a change in oxidation number of nitrogen from +3 to -1. This novel reaction provides a new route for the generation of arylnitrenium ions, a highly selective method for the detection of explosives in mixtures, and offers clues to the carcinogenic activity of nitroaromatics in vivo.     

Detection of explosives on solid surfaces by thermal desorption and ambient ion/molecule reactions

A simple, fast and direct method is presented for detecting traces of solid explosives on cotton swabs or in particulate samples: ions are transferred into a mass spectrometer after thermal desorption and corona discharge chemical ionization in ambient air; specificity is enhanced using ambient ion/molecule reactions or by conventional tandem mass spectrometry.     

Solid-state 109Ag CP/MAS NMR spectroscopy of some diammine silver(I) complexes

Solid-state cross-polarization magic-angle spinning (CP/MAS) NMR spectra were recorded for the compounds [Ag(NH3)2]2SO4, [Ag(NH3)2]2SeO4 and [Ag(NH3))]NO3, all of which contain the linear or nearly linear two-coordinate [Ag(NH3)2]+ ion. The 109Ag CP/MAS NMR spectra show centrebands and associated spinning sideband manifolds typical for systems with moderately large shielding anisotropy, and splittings due to indirect 1J(109Ag,14N) spin-spin coupling. Spinning sideband analysis was used to determine the 109Ag shielding anisotropy and asymmetry parameters Deltasigma and eta from these spectra, yielding anisotropies in the range 1500-1600 ppm and asymmetry parameters in the range 0-0.3. Spectra were also recorded for 15N and (for the selenate) 77Se. In all cases the number of resonances observed is as expected for the crystallographic asymmetric units. The crystal structure of the selenate is reported for the first time. One-bond (107, 109Ag,15N) coupling constants are found to have magnitudes in the range 60-65 Hz. Density functional calculations of the Ag shielding tensor for model systems yield results that are in good agreement with the experimentally determined shielding parameters, and suggest that in the solid compounds Deltasigma and eta are reduced and increased, respectively, from the values calculated for the free [Ag(NH3)2]+ ion (1920 ppm and 0, respectively), primarily as a result of cation-cation interactions, for which there is evidence from the presence of metal-over-metal stacks of [Ag(NH3)2]+ ions in the solid-state structures of these compounds.