Rhenium(V) and technetium(V) nitrido complexes with mixed tridentate π-donor and monodentate π-acceptor ligands

Mixed-ligand [M(N)(SNS)(PPh(3))] complexes (M = Tc, Re) (1, 2) were prepared by reaction of the precursor [M(N)Cl(2)(PPh(3))(2)] with ligand 2,2'-dimercaptodiethylamine [H(2)SNS = NH(CH(2)CH(2)SH)(2)] in refluxing dichloromethane/ethanol mixtures. In these compounds, 2,2'-dimercaptodiethylamine acts as a dianionic tridentate chelating ligand bound to the [M≡N](2+) group through the two π-donor deprotonated sulfur atoms and the protonated amine nitrogen atom. Triphenylphosphine completes the coordination sphere, acting as a monodentate ligand. [M(N)(NS(2))(PPh(3))] complexes can assume two different isomeric forms depending on the syn and anti orientations of the hydrogen atom bound to the central nitrogen atom of the SNS ligand with respect to the M≡N moiety. X-ray crystallography of the syn isomer of complex 2 demonstrated that it has a distorted trigonal bipyramidal geometry with the nitrido group and the two sulfur atoms defining the equatorial plane, the phosphorus atom of the monophosphine and the protonated amine nitrogen of the tridentate ligand spanning the two reciprocal trans positions along the axis perpendicular to the trigonal plane. Synthesis of the analogous Tc derivatives with tris(2-cyanoethyl)phosphine, [Tc(N)(SNS)(PCN)] [(PCN = P(CH(2)CH(2)CN)(3)], required the preliminary preparation of the new precursor [Tc(N)(PCN)(2)Cl(2)](2) (3), which was prepared by reacting [n-NBu(4)][Tc(N)Cl(4)] with a high excess of PCN. The crystal structure of compound 3 consists of a noncrystallographic centrosymmetric dimer of Tc(V) nitrido complexes having an octahedral geometry. In this arrangement, the apical positions are occupied by two tris(2-cyanoethyl)phosphine groups and the equatorial positions by the nitrido group whereas the two Cl(-) anions and one cyano ligand belong to the other octahedral component of the dimer. By reacting the new precursor [Tc(N)(PCN)(2)Cl(2)](2) with the ligand H(2)SNS the complex [Tc(N)(SNS)(PCN)] (5) was finally obtained in acetonitrile solution. The new Tc(III) complex trans-[Tc(PCN)(2)Cl(4)][n-NBu(4)] (4) was also isolated from the reaction solution used for preparing complex 3 as side product and characterized by X-ray diffraction. The crystal structure of 4 consists of independent trans-[TcCl(4)(PCN)(2)](-) anions situated on crystallographic centers of symmetry and tetrabutylammonium cations in general positions.     

An X-Ray Crystallographic Study of Five Compounds from a Series of 1,x-<Emphasis Type="Italic">bis</Emphasis>-(4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)alkanes

Abstract  

The crystal structures of a series of bis-(4-oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)alkanes, compounds 5 to 9, have been determined by single crystal X-ray diffraction analysis. The structural parameters of the triazinone rings in the five compounds do not display systematic differences with respect to those reported for a few analogous compounds. The benzotriazinone rings in 5 and 9 are almost perpendicular to the alkylic chain. The molecules in the crystal packing are linked by means of a weak C–H···X H-bond (X = N/O). Compound 6 has two independent molecules in the asymmetric unit; one of the molecules displays disorder within the benzotriazinone moiety linked in position 1 to the propane alkylic group. The disordered molecule displays two conformations of the benzotriazinone linked in position 1 to the propane bridge. Compound 8 also displays disorder within the benzotriazinone moiety linked in position 1 to the pentane alkylic spacer group. The molecules of compound 7, in the crystal packing, also form intra and inter-molecular C–H···X (X = N/O) hydrogen bonds. None of these compounds show any tendency to adopt a folded conformation with intramolecular π–π stacking between benzotriazinone units. Crystal data: 5 C₁₆H₁₂N₆O_2, monoclinic, space group P2 ₁ /c, a = 4.8370(2)?, b = 14.7845(7)?, c = 10.0837(4)?, β = 95.430(2)°, V = 717.88(6)?³, for Ζ = 2; 6 C₁₇H₁₄N₆O_2, triclinic, space group P-1, a = 7.4237(4)?, b = 14.4738(9)?, c = 15.0359(10)?, α = 91.871(3)°, β = 92.147(3)°, γ = 101.233(3)°, V = 1582.2(2)?³, for Ζ = 4; 7 C₁₈H₁₆N₆O_2, monoclinic, space group C2/c, a = 33.8886(10)?, b = 6.4593(2)?, c = 16.0608(6)?, β = 102.298(1)°, V = 3435.0(2)?³, for Ζ = 8; 8 C₁₉H₁₈N₆O_2, triclinic, space group P-1, a = 7.2592(2)?, b = 7.6795(2)?, c = 16.1003(5)?, α = 85.292(1)°, β = 81.367(1)°, γ = 88.377(1)°, V = 884.26(4)?³, for Ζ = 2; 9 C₂₀H₂₀N₆O_2, monoclinic, space group P2 ₁ /c, a = 7.2668(2)?, b = 4.5612(1)?, c = 28.1993(12)?, β = 97.313(2)°, V = 927.07(5)?³, for Ζ = 2.     

Some new routes for the preparation of 3-amino-2-phenyl-4(1H)-quinolinones from anthranilamides

[reaction: see text] Several new routes for the preparation of 3-amino-2-phenyl-4-1(H)-quinolinone 7a are compared. The most efficient is based on the cyclization of phenacyl anthranilamide 2a in the presence of (poly)phosphoric acid. The mechanisms of the rearrangements involved are discussed on the basis of the structures of isolated heterocyclic intermediates. The best methodology for the preparation of the title compound 7a was verified, and 10 other quinolinones 7 were prepared.     

Study of the Effects of Nonlinear Potential Sweeps on Voltammetry

Voltammetric methods use a constant sweep rate during the course of a scan. This paper reports a study of the influence of a nonconstant sweep rate on the voltammetric response. In this approach, either continuously increasing or continuously decreasing potential scan rates can be employed, unlike presently available methods which rely on a constant sweep rate. The voltammetric response of potassium ferrocyanide at a glassy carbon electrode was used as a model system to test the new method. The responses obtained using traditional staircase voltammetry (linear staircase voltammetry) and the new approach (nonlinear staircase voltammetry) were compared by experiment and by simulation. The new approach offers capability for signal enhancement, whereby enhanced current or enhanced peak shape can be obtained by choice of appropriate waveform parameters.     

Cosmological expansion and local systems: a Lemaître–Tolman–Bondi model

We propose a Lemaître–Tolman–Bondi system mimicking a two-body system to address the problem of the cosmological expansion versus local dynamics. This system is strongly bound but participates in the cosmic expansion and is exactly comoving with the cosmic substratum.     

Chelation of Theranostic Copper Radioisotopes with S-Rich Macrocycles: From Radiolabelling of Copper-64 to In Vivo Investigation

Copper radioisotopes are generally employed for cancer imaging and therapy when firmly coordinated via a chelating agent coupled to a tumor-seeking vector. However, the biologically triggered Cu²⁺-Cu⁺ redox switching may constrain the in vivo integrity of the resulting complex, leading to demetallation processes. This unsought pathway is expected to be hindered by chelators bearing N, O, and S donors which appropriately complements the borderline-hard and soft nature of Cu²⁺ and Cu⁺. In this work, the labelling performances of a series of S-rich polyazamacrocyclic chelators with [⁶⁴Cu]Cu²⁺ and the stability of the [⁶⁴Cu]Cu-complexes thereof were evaluated. Among the chelators considered, the best results were obtained with 1,7-bis [2-(methylsulfanyl)ethyl]-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). DO2A2S was labelled at high molar activities in mild reaction conditions, and its [⁶⁴Cu]Cu²⁺ complex showed excellent integrity in human serum over 24 h. Biodistribution studies in BALB/c nude mice performed with [⁶⁴Cu][Cu(DO2A2S)] revealed a behavior similar to other [⁶⁴Cu]Cu-labelled cyclen derivatives characterized by high liver and kidney uptake, which could either be ascribed to transchelation phenomena or metabolic processing of the intact complex.     

Phenylhydrazine–borane adduct—characterized in the solid state and in solution

The 1:1 phenylhydrazine–borane adduct, obtained from phenylhydrazine and sodium borohydride in acidic solution, was investigated by IR, NMR spectroscopy, and MS spectrometry. Ab initio MO calculations indicated the isomer in which the boron center is attached to the primary amino group as the more stable. This forecast was confirmed by solution‐state ¹H, ¹¹B, ¹³C, and ¹⁵N NMR spectroscopy, in agreement with the molecular structure in the solid state determined by X‐ray analysis. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:366–372, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10049     

Late-Stage Functionalisation of Pyridine-Containing Bioactive Molecules: Recent Strategies and Perspectives

Late-Stage Functionalisation (LSF) is an innovative technique that has been successfully applied to the C−H diversification of pharmaceuticals. However, LSF of the pyridine ring in drug-like molecules is often unselective. As a result, a mixture of structurally related products is obtained, thus making the purification tedious and time-consuming. This review shines a light on recent strategies addressing the selectivity issue in the LSF of complex natural products or drugs containing the pyridine moiety. Specifically, we have reviewed the efforts reported both in academia and industries with the hope of providing a guide for the LSF of elaborated pyridines.