The invention of new radical chain reactions. part X: High yield radical addition reactions of αβ-unsaturated nitroolefins. An expedient construction of the 25-hydroxy-vitamin D3 side chain from bi

Radicals derived from thiohydroxamic esters $\text{3}$ readily add to nitroolefins $\text{5}$ (Z = NO₂) to give good yields of α-nitrosulphides. These adducts, where the structure permits, are easily oxidised to carboxylic acids $\text{8}$ by treatment with alkaline hydrogen peroxide. Reductive cleavage to the corresponding aldehydes or ketones $\text{9}$ is efficiently carried out by the action of TiCl₃. Addition of methyl magnesium iodide to the methyl ketone derived from 3α-acetoxy 11-oxo cholanic acid gives steroid $\text{10}$ possessing the 25-hydroxycholesterol side chain of the vitamin D₃ metabotites. Radical additions to 1-phenylthio-2-nitropropene $\text{11}$ have been briefly studied.     

Nickel(II), palladium(II) and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2-ylthiourea

Platinum(II), palladium(II) and nickel(II) complexes with N-allyl-N′-pyrimidin-2-ylthiourea were synthesized in 1:1 and 1:2 [metal:ligand] stoichiometric ratios and characterized by elemental analyses, molar conductivities, magnetic susceptibilities and by i.r., u.v.-vis., ¹H- and ¹³C-n.m.r. and mass spectra. The ¹H- and ¹³C- n.m.r. chemical shifts reveal coordination of one pyrimidine-N and sulphur atoms to Pt^II and Pd^II. The i.r. spectra indicate that the ligand behaves as a neutral monodentate towards Ni^II; coordinates via a pyrimidine-N and as a bidendate towards Pd^II and Pt^II coordinates via thione-S and a pyrimidine-N. The magnetic moments and electronic spectral data suggest a square-planar geometry for Pt^II and Pd^II complexes, a mixture of square-planar and tetrahedral geometries for the tetracoordinate Ni^II complex and octahedral for the six-coordinate one. The E.I. mass spectra of the complexes showed some isotope ion peaks of [M]⁺ and fragments containing metals; assignments of fragments containing metal ions were supported by the appearance of their peaks among isotope clusters.     

Cobalt(II), nickel(II) and copper(II) complexes of 4-(sulfonylazido)phenylazopyrazolones

Transition metal complexes of Co^II, Ni^II and Cu^II with 4-(4-azidosulfophenylazo)-5-phenyl-3,4-dihydro-2H-pyrazol-3-oneHL¹, 4-(4-azidosulfophenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL² and 4-(3-azidosulfo-6-methoxyphenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL³ were prepared and characterized by elemental analyses, molar conductances and magnetic susceptibilities and by i.r., electronic and e.s.r. spectral measurements as well as thermal (d.t.a and t.g.a.) analysis. The i.r. spectra indicate that HL acts as a bidentate ligand coordinating via the azo and enolic-oxygen linkages. The electronic spectral data and magnetic moments suggest a tetragonally distorted octahedral geometry for the complexes having the formula ML₂·2H₂O, (M = Co^II, Ni^II and Cu^II), square pyramidal geometry for CuL ₂ ³ H₂O and tetrahedral geometry for CoL ₂ ³ . The X-band e.s.r. spectra of the copper(II) complexes reveal anaxial symmetry for both CuL ₂ ² 2H₂O and CuL ₂ ³ H₂O while CuL ₂ ¹ O is isotropic in the solid state at room temperature. The d.t.a. curves show two exothermic peaks for all three complexes CoL ₂ ³ ,NiL ₂ ³ 2H₂O and CuL ₂ ³ H₂O and one endothermic peak for the latter two aqua complexes.     

Synthesis of 3-arylpiperidines by a radical 1,4-aryl migration

[reaction: see text] A route to 3-arylpiperidines, 3-arylpyridines, and 5-arylpiperidin-2-ones involving a radical 1,4-aryl migration has been explored. The sequence requires a xanthate addition to an N-allylarylsulfonamide, followed by acetylation and treatment with dilauroyl peroxide to give the 1,4-aryl transfer product, which upon acidic hydrolysis affords the desired piperidine derivative.     

Synthesis and Characterization of Variable-valent Imidorhenium Species. A Family of Imidorhenium(VI) Amide Complexes and their Imidorhenium(V) Imine Precursors Related by Oxygen Atom Transfer

The synthesis of imidorhenium(V) [Re(NAr)Cl₃(L)] complexes is reported. Their reaction with dilute HNO₃ furnishes [Re(NAr)Cl₃(L′)] species incorporating monoionized iminoamide ligands (the ligands are abbreviated as L and L′ respectively). The iminoamide complexes exhibit sextet EPR spectra in CH₂Cl₂ solution at room temperature. They are electroactive in MeCN solution and to display two quasi reversible responses near 0.2 and 1.6 V which can be attributed to Re^V→Re^VI and Re^VI → Re^VII oxidations respectively. One of the [Re(NAr)Cl₃(L)] complexes has been structurally characterized. The trans influence of the amide nitrogen considerably lengthens the Re–N bond lying trans to the imido group. The triply bonded ReN–C moiety is linear.     

Spectroscopic and Electrochemical Studies of Some Molybdenum and Ruthenium Complexes of N-[(2-pyridyl)methyl]-2,2′-dipyridylamine

Interaction of the tripodal ligand N-[(2-pyridyl)methyl]-2,2′-dipyridylamine (pmdpa) with [Mo(CO)₆] under reduced pressure gave two complexes [Mo(CO)₄(pmdpa)] and [Mo(CO)₂(pmdpa)₂], depending on the mole ratio and reaction time. The i.r. spectra of the two complexes gave patterns in the metal carbonyl region confirming the proposed structures. Reaction of [Ru₃(CO)₁₂] with pmdpa in benzene gave the mononuclear complex [Ru(CO)₃(pmdpa)]. The electronic absorption spectra of the complexes exhibited visible transitions due to metal-to-ligand charge transfers. Electrochemical investigation of the complexes showed some irreversible and quasi-reversible redox reactions due tautomeric interconversions through electron transfer.     

A Gradient-Descent Method for Curve Fitting on Riemannian Manifolds

Given data points p ₀,…,p _N on a closed submanifold M of ℝ ⁿ and time instants 0=t ₀<t ₁<⋅⋅⋅<t _N =1, we consider the problem of finding a curve γ on M that best approximates the data points at the given instants while being as “regular” as possible. Specifically, γ is expressed as the curve that minimizes the weighted sum of a sum-of-squares term penalizing the lack of fitting to the data points and a regularity term defined, in the first case as the mean squared velocity of the curve, and in the second case as the mean squared acceleration of the curve. In both cases, the optimization task is carried out by means of a steepest-descent algorithm on a set of curves on M. The steepest-descent direction, defined in the sense of the first-order and second-order Palais metric, respectively, is shown to admit analytical expressions involving parallel transport and covariant integral along curves. Illustrations are given in ℝ ⁿ and on the unit sphere.     

A Molecular Magnet Confined in the Nanocage of a Globular Protein

The effect of confinement and energy transfer on the dynamics of a molecular magnet, known as a model system to study quantum coherence, is investigated. For this purpose the well‐known polyoxovanadate [V₁₅As₆O₄₂(H₂O)]^6? (V₁₅) is incorporated into a protein (human serum albumin, HSA) cavity. Due to a huge overlap of the optical absorption spectrum of V₁₅ with the emission spectrum of a fluorescence center of HSA (containing a single tryptophan residue), energy transfer is induced and probed by steady‐state and time‐resolved fluorescence. The geometrical coordination and the distance of the confined V₁₅ to the tryptophan moiety of HSA are investigated at various temperatures. This effect is used as a local probe for the thermal denaturation of the protein at elevated temperatures.     

The plumbide CeZnPb – Structure,magnetism, and chemical bonding

The plumbide CeZnPb was synthesized from the elements in a sealed tantalum ampoule. Its YPtAs-type structure was refined on the basis of single-crystal X-ray diffraction data: P6₃/mmc, a = 463.7(2) and c = 1669.6(6) pm, wR2 = 0.1161, 189 F² values, and 12 variables. CeZnPb crystallizes with a superstructure of AlB₂. The zinc and lead atoms form puckered [Zn₃Pb₃] hexagons, which are stacked in a sequence ABB′A′. The Zn–Pb distances within the layers are 278 pm. The shortest interlayer distance occurs between the zinc atoms of adjacent layers (305 pm). Susceptibility measurements of CeZnPb show Curie–Weiss behavior with an experimental magnetic moment of 2.47(1) μ_B/mol CeZnPb. CeZnPb shows two antiferromagnetic transitions at T_N1 = 3.8 K and T_N2 = 2.6 K. Magnetization measurements at 2 K show two metamagnetic transitions at critical fields of approximately 1.1 and 7.0 kOe, underlining the antiparallel spin alignment at zero field. The electronic and magnetic structure is discussed based on scalar relativistic computations using the augmented spherical wave (ASW) method within density functional theory (DFT). As a result, our calculations employing the generalized gradient approximation (GGA) reveal a delicate competition of ferro and antiferromagnetic interactions. Only after properly taking into account the electronic correlations present in CeZnPb via a GGA + U treatment we are able to correctly describe the antiferromagnetic ground state. In addition, our calculations give a clue to the metamagnetic transitions as being due to the inherent geometric frustration of the cerium spin system.     

Empirical low energy values for methane transitions in the 5852-6181 cm region by absorption spectroscopy at 81 K

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by direct absorption spectroscopy between 1.62 and 1.71 μm (5852-6181 cm⁻¹) using a newly developed cryogenic cell and a series of distributed feedback (DFB) laser diodes. The minimum value of the measured line intensities is on the order of 3 × 10⁻²⁶ cm/molecule The investigated spectral range corresponds to the high energy part of the tetradecad dominated by the 2ν₃ band for which a theoretical treatment is not yet available. The positions and strengths at 81 K of 2187 transitions were obtained from the spectrum analysis. From the values of the line strength at liquid nitrogen and room temperatures, the low energy values of 845 transitions could be determined. The obtained results are discussed in relation with the previous work of Margolis and compared to the line list provided by the HITRAN database.