Synthesis,crystal and molecular structure and spectroscopic studies (i.r., electronic,13C-n.m.r. and Mössbauer) of the perchlorate of nitrosyltetracyanoiron(II)-μ-cyano-pentaamminecobalt(III)trihydrate and its chromium(III) analogue

Summary The two new title compounds have been synthesized and characterized by x-ray crystal structure and spectroscopic measurements. Both compounds are air-stable and isomorphous. The crystal system, space group and Z for both compounds are: hexagonal, p6₁ and 6. Lattice constants for the Co^III and Cr^III complexes are as follows:a = 9.674(3) Å,c = 37.196(6) Å anda = 9.786(3) Å,c = 37.852(6) A, respectively. The molecular structure shows a great distortion in the Fe-C-N-M torsion angle [–46.8(7)° and –51.3(7)°, respectively] which has been interpreted as due to the presence of the NO ligand. The spectral studies confirm the presence of the -cyano ligand by the clear splitting of the (CN) stretching vibration atca. 2200 cm^–1 and the shift of 15–20 nm towards higher frequencies in the first d-d transition of M^III. The¹³C-n.m.r. spectrum of the diamagnetic Co^III complex confirms the presence of the -cyano ligand in solution and, as in the solid phase, the bridging group iscis to the NO of the nitroprusside. The Mössbauer spectra show that the principal axis component of electric field gradient tensor will most likely be directed in the Fe-NO direction (as in the nitroprusside ion) and not towards the CN bridge.     

Dehydrogenation with phenylseleninic anhydride in the total synthesis of ergot alkaloids

The standardised procedure for dehydrogenation of indolines into indoles with phenylseleninic anhydride $\text{1}$ was successfully applied to the final steps in the total synthesis of ergot alkaloids.     

Acid-Catalysed Backbone Rearrangement of cholesta-6,8(14)-dienes

Rearrangement of 5α- and 5β-cholesta-6,8(14)-dienes ( 13a and 13b , resp.) in the presence of anhydrous toluene-4-sulfonic acid in acetic acid leads to 5α- and 5β-12(13 → 14)-abeo-cholesta-8,13(17)-dienes ( 15a and 15b , resp.) via 5α- and 5β-cholesta-8,14-dienes ( 14a and 14b , resp.), respectively. Epimerization at C(20) of the spirosteradienes 15a and 15b occurs with increasing reaction time. Molecular-mechanics calculation of the relative stabilities of these compounds and of congeners thereof is in agreement with the observed reaction pathway.     

Second-order quantum similarity measures from intracule and extracule densities

The calculation of quantum similarity measures from second-order density functions contracted to intracule and extracule densities obtained at the Hartree-Fock level is presented and applied to a series of atoms, (He, Li, Be, and Ne), isoelectronic molecules (C₂H₂, HCN, CNH, CO, and N₂), and model hydrogen-transfer processes (H₂/H⁺, H₂/Hot, H₂/H⁻). Second-order quantum similarity measures and indices are found to be suitable measures for quantitatively analyzing electron-pair density reorganizations in atoms, molecules, and chemical processes. For the molecular series, a comparative analysis between the topology of pairwise similarity functions as computed from one-electron, intracule, and extracule densities is carried out and the assignment of each particular local similarity maximum to a molecular alignment discussed. In the comparative study of the three hydrogen-transfer reactions considered, second-order quantum similarity indices are found to be more sensitive than first-order indices for analyzing the electron-density reorganization between the reactant complex and the transition state, thus providing additional insights for a better understanding of the mechanistic aspects of each process. Received: 7 July 1997 / Accepted: 29 October 1997     

Cage‐like Fe,Na‐Germsesquioxanes: Structure,Magnetism, and Catalytic Activity

A series of four unprecedented heterometallic metallagermsesquioxanes were synthesized. Their cage‐like architectures have a unique type of molecular topology consisting of the hexairon oxo {Fe₆O₁₉} core surrounded in a triangular manner by three cyclic germoxanolates [PhGe(O)O]₅. This structural organization induces antiferromagnetic interactions between the Fe^III ions through the oxygen atoms. Evaluated for this first time in catalysis, these compounds showed a high catalytic activity in the oxidation of alkanes and the oxidative formation of benzamides from alcohols.     

Use of ionic liquids in the platinum- and gold-catalyzed cycloisomerization of enyne systems

The platinum- and gold-catalyzed cycloisomerization of enyne systems has been carried out in various ionic liquids (ILs). In some cases, better selectivities and shorter reaction times have been observed compared to conventional conditions.     

Absorbing boundary conditions for the one-dimensional Schrödinger equation with an exterior repulsive potential

Mathematical constructions and comparisons of accurate absorbing boundary conditions for the one-dimensional Schrödinger equation with a general variable repulsive potential are developed. Stable semi-discretization schemes are built for the associated initial boundary value problems. Finally, some numerical simulations give a comparison of the various absorbing boundary conditions and show that they yield accurate computations.