Novel crowned-porphyrin ligands. Synthesis and conformational studies

Three new macromolecules—a cryptand, a bis-macrocycle, and a tris-macrocycle—have been synthesized as chelating ligands for cation binding. They result from the surprisingly simple reaction of various bis-functionalized meso-aryl porphyrins with a diaza-crown ether coupled one to each other through either one or several urea linkage(s). Indeed, the latter induces some additional rigidity in comparison with the usual amide linkage found in such macromolecules. Various strategies are reported to optimize the yield of the reaction towards the formation of a cofacial singly-linked crown-porphyrin, which is the most promising ligand to stabilize large cations such as bismuth(III) as the angle between the two macrocycles can vary.     

First synthesis of picealactone C. A new route toward taxodione-related terpenoids from abietic acid

A new route to 12-hydroxyabietic acid (10) and related compounds from abietic acid (12), via acetoxyalcohol 15, is reported. Utilizing this, the first synthesis of picealactone C (5) was achieved. The synthesis of natural 12-hydroxydehydroabietic acid (8), 18-hydroxyferruginol (9) and methyl 12α-hydroxyabietate (11) is also reported.     

Photoionization of highly charged ions using an ECR ion source and undulator radiation

Photoionization of Xe4+ to Xe7+ ions was studied by combining an electron cyclotron resonance ion source with synchrotron radiation. Multiconfiguration Dirac-Fock calculations were performed to interpret the data. Many autoionization lines were measured and identified, resulting from excitation of a 4d electron into nf and np orbitals followed by Auger decay of the excited states. Continuum photoionization is negligible for the higher members of the isonuclear series.     

Structure elucidation and vasodilator activity of methoxy flavonols from Calycotome villosa subsp. intermedia

Two flavonols identified as 3,5,7,4′-tetrahydroxy-3′-methoxyflavone (1) and 3,5,7,4′-tetrahydroxy-8-methoxyflavone (2) were isolated from the seeds of Calycotome villosa subsp. intermedia. The structure elucidation of the isolated compounds was performed by the spectroscopic methods (UV, IR, ¹H NMR, ¹³C NMR and MS) and also by a single crystal X-ray analysis in the case of compound (2). Vasodilator activity of compound (2) was demonstrated in isolated rat aorta contracted with high KCl or with noradrenaline.     

Properties of a Tunable Multinuclear Nickel Polyoxotungstate Platform

A series of hybrid nickel bisphosphonate (BP) polyoxometalates (POMs) has been isolated. The complexes NaK‐Ni₇‐Ale₂ (Ale=[H₂O₃PC(C₃H₆NH₂)(OH)PO₃H₂]) and NaNH₄‐Ni₇‐Ale₂ are both made of two {PW₉O₃₄} fragments enclosing a heptanuclear Ni^II core connected to two alendronate ligands. By pre‐functionalising the alendronate moiety through the amino group, the naphthalene (napht) derivative Ni₇‐(AleNapht)₂ and the compounds Ni₇‐(AlePy₂Ni)₂ (py=pyridyl) and Ni₇‐(AleAc₂Ni)₂ (Ac=acyl) have been obtained. Compared with the NaK‐Ni₇‐Ale₂ species, these last two complexes contain two additional Ni^II centres connected through two bis(2‐pyridylmethyl)amine or two iminodiacetate groups, respectively. This results show that it is possible to functionalise the heptanuclear POM in a controlled manner. Quantification of the magnetic interactions in NaK‐Ni₇‐Ale₂ revealed that in the {Ni₇} core, ferromagnetic interactions are predominant, with a S=5 ground state. Magnetisation versus dc field sweeps on a single crystal of NaK‐Ni₇‐Ale₂ exhibited hysteresis at low temperature. ¹H and ³¹P NMR studies in aqueous solution performed on NaK‐Ni₇‐Ale₂ and Ni₇‐(AleNapht)₂ evidenced that the PW₉/Ni₇/bisphosphonate assembly is stable in solution. This was completed by ³¹P magic angle spinning (MAS) investigations and confirmed by ¹H DOSY experiments. The electrochemistry of these compounds proceeds through two well‐defined four‐electron chemically reversible waves in a medium at pH 6. NaK‐Ni₇‐Ale₂ proved to be efficient for the electrocatalytic reduction of nitrate, nitrite and nitrous oxide. Remarkably, its electrocatalytic efficiency for nitrate reduction is approximately three times higher than those previously reported for POMs in a medium at pH >4 under the same potential. The catalytic properties of two representatives of the hybrid family were also examined. It is shown that these nickel bisphosphonate polyoxotungstates are pre‐catalysts for the oxidation of alcohols into ketones or carboxylic acids, depending on the classes of alcohols considered, the stoichiometric oxidant used being H₂O₂. Noticeably, it has been found that an analogous cobalt bisphosphonate polyoxotungstate complex does not present any related activity, highlighting the crucial role of the 3d cations on the catalytic process.     

Quadrupole moments and nucleon excitation strengths in even-A Sm isotopes

We present a coherent coupled-channel analysis of 7 MeV neutron and 16 MeV proton elastic and inelastic scattering from ^{148, 152, 154}Sm. The optical potential and nuclear deformation parameters are determined so as to fit not only these elastic and inelastic scattering data but also the low-energy neutron scattering properties and the total cross sections over a wide energy range. This analysis provides evidence of the same excitation strengths for both projectiles in the case of ^{152, 154}Sm, and of a smaller excitation strength for the proton than for the neutron in case of ¹⁴⁸Sm. Moreover the quadrupole moments of these deformed optical potentials are in good agreement with those extracted from Coulomb excitation measurements and from nuclear matter distribution calculations.     

Structural characterisation of the first mononuclear bismuth porphyrin

A single carboxylate picket bismuth porphyrin has been characterised in the solid state as the first instance of a non-dimeric structure; the carboxylate picket, bent over the macrocycle, is coordinated to the bismuth, inducing a significant distortion of the porphyrin core.     

Polymeric (O‐ethyl di­thio­carbonato)silver(I)

The title compound, [Ag(C₃H₅OS₂)]_n, is polymeric in the solid state and adopts a layered structure in which each Ag atom is five‐coordinated in a distorted trigonal‐bipyramidal geometry defined by four S atoms belonging to four different xanthate groups and by a neigbouring Ag atom [Ag⃛Ag = 3.0540 (8) Å]. Each S atom is three‐coordinated to one C and two Ag atoms. The structure can be envisaged as being formed by Ag₂(S₂COEt)₂ units in which every S atom is bonded to another Ag atom from a different unit and the Ag atoms are also bonded to two different S atoms of two other units. The result is a two‐dimensional network of condensed metallacycles of six or eight atoms.     

Reactivity of molecular dioxygen towards a series of isostructural dichloroiron(III) complexes with tripodal tetraamine ligands: general access to mu-oxodiiron(III) complexes and effect of alpha-fluorination on the reaction kinetics

We have synthesized the mono, di-, and tri-alpha-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F(2)TPA and F(3)TPA, respectively. Fluorination at the alpha-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45-70 mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F(2)TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl(2). All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable mu-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three mu-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the kappa(4)N coordination mode. With FTPA, the compound is a neutral mu-oxodiiron(III) complex with a kappa(3)N coordination mode of the ligand. Oxygenation of the F(2)TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all mu-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of mu-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90 % conversion over 40 h, the monofluorinated ligand provides a complex that has fully reacted after 30 h, whereas the reaction time for the complex with the difluorinated ligand is only 10 h. Analysis of the spectroscopic data reveals that formation of the mu-oxo complexes proceeds in two distinct reversible kinetic steps with k(1) approximately 10 k(2). For TPAFeCl(2) and FTPAFeCl(2) only small variations in the k(1) and k(2) values are observed. By contrast, F(2)TPAFeCl(2) exhibits k(1) and k(2) values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of mu-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials.