Audrey Auffrant

Phosphasalen Yttrium Complexes: Highly Active and Stereoselective Initiators for Lactide Polymerization

Preparation and characterization of three yttrium alkoxide complexes with new phosphasalen ligands are reported. The phosphasalens are analogues of the well-known salen ligands but with iminophosphorane donors replacing the imine functionality. The three yttrium alkoxide complexes show mono- and dinuclear structures in the solid state, depending on the substituents on the ligand. The new ligands and complexes are characterized using multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction experiments. The complexes are all rapid initiators for lactide polymerization; they show excellent polymerization control on addition of exogeneous alcohol. The mononuclear complex shows extremely rapid rates and a high degree of stereocontrol in rac-lactide polymerization, yielding heterotactic PLA (P(s) of 0.9). The phosphasalens are, therefore, excellent ligands for lactide ring-opening polymerization catalysis showing superior rates and stereocontrol versus salen ligands, which may be related to their excellent donating ability and the high degrees of steric protection they can confer.

A new and convenient approach towards bis(iminophosphoranyl)methane ligands and their dicationic, cationic, anionic and dianionic derivatives

The availability of bis(aminophosphoranes) 2a–c through a straightforward synthesis yielded access to a whole family of N,N ligands via sequential deprotonation. The obtained cationic 3a–c, neutral 4a–c, anionic 5a–c and dianionic 6a–c compounds were fully characterized by NMR and X-ray crystallography. Monocations 3a–c were shown to result from the deprotonation of 2a–c at the bridging methylene carbon. DFT calculations evidenced a substantial negative charge at this carbon. For the neutral bis(iminophosphoranes) 4a–c, two different forms were experimentally observed depending on the nature of the substituent at nitrogen. In the presence of an aryl group, a bis(iminophosphorane) is obtained whereas with alkyl substituent a tautomeric form resulting from a (1,3) hydrogen shift is observed. Theoretical studies were in good agreement with experimental results showing that these two forms are close in energy. The structure obtained for monoanion 5a reveals that a substantial interaction occurs between the anionic carbon and the lithium cation. The X-ray crystal structure of the optically pure dianion 6b has also been recorded.

Highly efficient P–N nickel(II) complexes for the dimerisation of ethylene

New P-N ligands featuring a phosphino group and an iminophosphorane moiety were successfully employed in the nickel-catalysed dimerisation of ethylene.

Cobalt-Catalyzed Electrophilic Amination of Arylzincs with N-Chloroamines

Roles reversed: An efficient cobalt-catalyzed electrophilic amination of arylzinc reagents has been achieved. A variety of functionalized arylzincs and N-chloroamines were coupled under mild conditions (see scheme). Both secondary and tertiary arylamines were obtained in moderate to excellent yields.

Synthesis of nitrile ligands bearing tricarbonyl (η6-arene)chromium complexes and conjugated spacers

Abstract The synthesis of nitrile ligands linked to tricarbonyl (η 6 -arene)chromium complexes by conjugated spacers is performed by reacting aromatic bromo nitrile derivatives with tricarbonylchromium-complexed phenylacetylene using Sonogashira coupling reaction.

Chromium (III)-bis(iminophosphoranyl)methanido complexes: synthesis, X-ray crystal structures and catalytic ethylene oligomerization

Bis(aminophoshonium) salts derived from bis(diphenylphosphino)methane were prepared and triply deprotonated with potassium hexamethyldisilazane to yield the corresponding bis(iminophosphoranyl)methanides, which were then subjected to coordination with CrIIICl3(THF)3. Binuclear complexes of type [(HC(PPh2NR)2Cr(μ-Cl)(Cl))2] (R = iPr, tBu) with an octahedral coordination geometry and a long C–Cr bond were obtained and structurally characterized. In the case of R = o-MeO-C6H4, a monomeric species featuring no C–Cr bond is observed. Preliminary evaluation of catalytic activities of these complexes in ethylene oligomerization and polymerization is reported.

Organochromium/organoiron dipoles comprising (η6-arene)chromium and (η5-cyclohexadienyl)iron(1+) complexes linked with conjugated spacers

Abstract The synthesis of novel bimetallic organochromium/organoiron monocation dipoles comprising π-conjugated complexes linked with conjugated spacers has been performed utilising Stille and Sonogashira coupling reactions. This work establishes a general strategy for the synthesis of mixed-metal chromium/dipole complexes for evaluation for nonlinear optical effects by hyper-Rayleigh scattering.

A Tetracoordinated Phosphasalen Nickel(III) Complex

The oxidation of a Ni(II) complex bearing a tetradentate phosphasalen ligand, which differs from salen by the presence of an iminophosphorane (PN) in place of an imine unit, was easily achieved by addition of a silver salt. The site of this oxidation was investigated with a combination of techniques (NMR, EPR, UV/Vis spectroscopy, X-ray diffraction, magnetic measurements) as well as DFT calculations. All data are in agreement with a high-valent Ni(III) center concentrating the spin density. This markedly differs from precedents in the salen series for which oxidation on the metal was only observed at low temperature or in the presence of additional ligands or anions. Therefore, thanks to the good electron-donating properties of the phosphasalen ligand, [Ni(Psalen)](+) represents a rare example of a tetracoordinated high-valent nickel complex in presence of a phenoxide ligand.

Interplay between Hydrido/Dihydrogen and Amine/Amido Ligands in Ruthenium-Catalyzed Transfer Hydrogenation of Ketones

This work describes the synthesis of three key intermediates of Noyori-type catalytic systems that are active precatalysts for the transfer hydrogenation of acetophenone. Isolation of the cationic chloro(dihydrogen) complex [RuCl(H(2))(H(2)NNPP)(PCy(3))][BArf(4)] provides a facile synthetic route to the corresponding cationic and neutral hydrido complexes, and the series highlights the links between hydride/dihydrogen and amine/amido ligands in neutral and cationic species.

Iminophosphorane-based [P2N2] rhodium complexes: synthesis, reactivity, and application in catalysed transfer hydrogenation of polar bonds

[Rh(P2N2)X] complexes (2-X, X = Cl, BF4) featuring a tetradentate iminophosphorane phosphine ligand were synthesised and characterised. X-Ray analysis provides evidence for a square planar geometry without coordination of the chloride anion. These complexes proved to be air-sensitive, and their oxidation to Rh(III) complexes 3-X was observed in air. The controlled reaction of 2-BF4 with one equivalent of hexachloroethane yielded [Rh(P2N2)Cl2(BF4)] (3-BF4). Direct synthesis of 3-Cl can also be achieved by coordination of the [P2N2] ligand to [RhCl(THT)3] (THT = tetrahydrothiophene). The reactivity of Rh(I) complexes 2 was further investigated, and no reaction was observed with silanes, aryl halides, or pinacolborane, although decomposition was observed under 1 atm of H2 upon prolonged heating. Interestingly, reduction of complex 3-Cl was observed by NMR upon treatment with silanes or sodium isopropoxide. Therefore, complex 3-Cl was used for catalytic transfer hydrogenation of polar bonds. The reduction of aromatic and aliphatic ketones can be carried out using 1% catalyst and 10% sodium isopropoxide, while imines are partially reduced under these conditions.