Synthesis,Structure, and Highly Efficient Copper‐Catalyzed Aziridination with a Tetraaza‐Bispidine Ligand

The distorted trigonal‐bipyramidal Cu^II complex [Cu(L¹)(NCCH₃)]²⁺ of the novel tetradentate bispidine‐derived ligand L¹ with four tertiary amine donors (L¹=1,5‐diphenyl‐3‐methyl‐7‐(1,4,6‐trimethyl‐1,4‐diazacycloheptane‐6‐yl)diazabicyclo[3.3.1]nonane‐9‐one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper–bispidine complexes and the novel L¹‐based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture.     

Influence of intermolecular amide hydrogen bonding on the geometry, atomic charges, and spectral modes of acetanilide: An ab initio study

Acetanilide, a compound of pharmaceutical importance possessing pain-relieving properties due to its blocking the pulse dissipating along the nerve fiber, is subjected to vibrational spectral investigation using NIR FT Raman, FT-IR, and SERS. The geometry, Mulliken charges, and vibrational spectrum of acetanilide have been computed using the Hartree-Fock theory and density functional theory employing the 6-31G (d) basis set. To investigate the influence of intermolecular amide hydrogen bonding, the geometry, charge distribution, and vibrational spectrum of the acetanilide dimer have been computed at the HF/6-31G (d) level. The computed geometries reveal that the acetanilide molecule is planar, while twisting of the secondary amide group with respect to the phenyl ring is found upon hydrogen bonding. The trans isomerism and “amido” form of the secondary amide, hyperconjugation of the C=O group with the adjacent C-C bond, and donor-acceptor interaction have been investigated using computed geometry. The carbonyl stretching band position is found to be influenced by the tendency of the phenyl ring to withdraw nitrogen lone pair, intermolecular hydrogen bonding, conjugation, and hyperconjugation. A decrease in the NH and C=O bond orders and increase in the C-N bond orders due to donor-acceptor interaction can be observed in the vibrational spectra. The SERS spectral analysis reveals that the flat orientation of the molecule on the adsorption plane is preferred.     

The Role of the “Ligand Periphery” in the Coordination of Tripodal Triamidostannates(II) to Iridium: Simple Ligation vs. Cyclometallation

Reaction of the triamidostannates(II) MeSi{SiMe₂N(3,5‐xyl)}₃SnLi(OEt₂) ( 2a ) and MeSi{SiMe₂N(p‐tol)}₃SnLi(OEt₂) ( 2b ) with [IrCl(CO)(PPh₃)₂] gave the Ir^I‐Sn complex [MeSi{SiMe₂N(3,5‐xyl)}₃SnIr(PPh₃)₂(CO)] ( 3a ) for the former. In contrast, for the tolyl stannate CH‐activation occurred to give the Ir^III compound [MeSi{SiMe₂N(p‐tol)}₂{SiMe₂N(2‐C₆H₃‐4‐CH₃)}SnIr(H)(PPh₃)₂(CO)] ( 3b ). The latter is thus avoided by introduction of suitably placed substituents in the peripheral aryl groups of the triamidostannate ligand.     

Calibration of solid sampling Zeeman atomic absorption spectrophotometry by extrapolation to zero matrix

Summary A new method is described for the calibration of solid sampling Zeeman atomic absorption spectrophotometry, which can be applied independently of the use of certified reference materials. The specific signal (peak height divided by analyte mass or peak height divided by sample mass, for standard and sample, resp.) is plotted as a function of the analyte or the sample mass, and the line is extrapolated to zero mass. It is believed that this gives a specific signal not influenced by deviations from linearity of the calibration curve and free from matrix effects. The method yielded good results for Zn, Cd and Pb in several certified reference materials.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

Ionization of hydrogen by a relativistic heavy projectile

Using a relativistic analogue of the classical trajectory Monte-Carlo method we investigate the influence of the magnetic field of a relativistic heavy projectile on the ionization cross section of hydrogen. In particular we focus our attention on the angular and energy distribution of the emitted delta electrons.     

On the usefulness of SS-ZAAS for the microhomogeneity control of CRM''s

Summary A method is discussed for the quantitative evaluation of the minimum sample size of a solid certified reference material (CRM) and for the calculation of the uncertainty to be attributed to the CRM if very small samples are used. The method requires a preliminary microhomogeneity control. Solid sampling Zeeman atomic absorption spectrometry (SS-ZAAS) is particularly suited for such controls, as it allows fast submilligram analysis without sample pretreatment and does not necessarily need calibration.Presented at the 5th International Colloquium on Solid Sampling with Atomic Spectroscopy, May 18–20, 1992; Geel, Belgium. Papers edited by R. F. M. Herber, Amsterdam     

Microwave-induced plasma emission spectrophotometer combined with a photodiode array monitor for capillary column gas chromatography

A microwave-induced plasma emission spectrophotometric detector (MIPD) was used as an element-specific detector for capillary column gas chromatography. The atmospheric pressure microwave helium plasma generated with an original device called a SURFATRON was used as an atomization and excitation source. Combining a photodiode array spectrophotometer with the above system made the emission spectrophotometric detector very powerful. A wide range of spectra could be instantly monitored without any mechanical device. However, the spectrum of atmospheric helium emission plasma was complicated by the presence of air around the plasma discharge. An on-line background correction scheme was developed to handle such complicated spectra.     

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