Synthesis of axially chiral biaryl compounds by asymmetric catalytic reactions with transition metals

International audienceAxially chiral biaryl structures are unique systems encountered in various synthetic compounds such as BINAP and BINOL, polymers, but also in natural products presenting a pharmaceutical interest such as Vancomycin, Steganacin or Korupensamine. The axial chirality of these products, so-called atropisomerism, is induced by the restricted rotation around the aryl–aryl bond. This review will summarize the different strategies imagined by chemists to control such chirality, focusing on asymmetric catalytic processes with transition metals. Only transition metal complexes bearing chiral ligands will be considered and the core of this review will consist of the enantioselective coupling of two achiral substrates

Rhodium nanoparticles stabilized by ferrocenyl-phosphine ligands: synthesis and catalytic styrene hydrogenation

International audienceA series of ferrocenylphosphine-stabilized rhodium nanoparticles has been prepared in one pot from the organometallic [Rh(η3-C3H5)3] precursor. This complex has been decomposed by hydrogen treatment (3 bar) in dichloromethane in the presence of five different ferrocene-based phosphine ligands. Very small rhodium nanoparticles in the size range of 1.1–1.7 nm have been obtained. These nanoparticles have shown activity in a model catalytic reaction, namely the hydrogenation of styrene. These results evidence that the metal surface is not blocked despite the steric bulk of the stabilizing ligands. Moreover, certain selectivity has been observed depending on the ligand employed. To the best of our knowledge, such a type of compound has not yet been used for stabilizing metal nanoparticles and our findings highlight the interest to do so

Straightforward synthesis of ferrocenyl allylic thioethers

International audienceThe new ferrocenyl allylic thioethers FcCH = CHCH2SR (2a-e) and FcCH(SR)CH = CH2 (3a-e) (R = Ph, a; 2-naphthyl, b; 3,5-C6H3Me2, c; iPr, d; tBu, e) were synthesized in good yields from ((2-ferrocenylvinyl)methyl)trimethylammonium iodide, [1]+I- and the corresponding thiol RSH. With sufficiently strong bases to fully deprotonate the thiol, good to excellent regioselectivities (88-99%) in favor of the linear isomer 2 were obtained. The mol. structures of 2a and 2b were obtained by X-ray diffraction on monocrystals. A mechanistic proposal based on exptl. data and supported by calcns. is also presented, underlying the role of the base in the reaction regioselectivity

Corrosion of carbon steel components in the French high-level waste program evolution of disposal concept and selection of materials.

International audienceIn France, the reference concept for the geological disposal of high-level waste (HLW) consists of horizontal micro-tunnels, containing carbon steel casing and overpacks (around a stainless steel container containing vitrified waste). The overpacks and casing will be exposed to an environment that will evolve over time: from a hot and humid atmosphere containing oxygen, to an anoxic environment saturated with water at the geothermal temperature. Lots of corrosion experiments have been performed in representative environments to study steel corrosion modes (general corrosion, pitting and crevice corrosion, stress corrosion cracking, hydrogen embrittlement…) while taking into account the influence of temperature, radiation, mechanical stresses and microorganisms. Some key results have influenced the design of the HLW disposal cell, including the carbon steel grades and dimensions of the casing and overpacks, or the addition of an alkaline grout material between the casing and the host rock

Synthesis and characterization of new chiral P,O ferrocenyl ligands and catalytic application to asymmetric Suzuki-Miyaura coupling

International audienceThe synthesis and characterization of a series of novel chiral P,0 ferrocenyl ligands obtained from the reaction of racemic (9) or enantiomerically pure ((R)-9 or (S)-9) 2-thiodiphenylphosphino(hydroxymethyl) ferrocene with alcohols is described. The use of para-methylbenzylalcohol, ethanol and (1R,2S,5R)-me ntho I gives rise to three ligands (10,11 and 12 respectively) possessing planar chirality. All compounds have been characterized by multinuclear NMR and mass spectrometry. Compounds 12 and 12a (the protected form of phosphine 12 with a P=S bond) present both planar and central chirality giving rise to two diastereoisomers differing in configuration (R or S) of the ferrocenyl fragment. Compound (S)-12a has been characterized by single-crystal X-ray diffraction. Kinetic studies realized at three different temperatures (40, 50 and 60 C) show good yields in the asymmetric Suzuki Miyaura synthesis of substituted binaphthalenes using 1-naphthalenboronic acid and 1-bromo-2-methylnaphthalene. The best enantioselectivity (37% ee) was obtained with ligand (R)-12

Corrosion of carbon steel components in the French high-level waste program evolution of disposal concept and choices of materials.

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Ruthenium p-cymene iminophosphonamide complexes: Activation under basic conditions and transfer hydrogenation catalysis

International audienceComplex [(η6-Cym)RuCl(NPN)] Cym = p-cymene; NPN = (pTolN)2PPh2 (1) yields a thermally sensitive hydride derivative [(η6-Cym)RuH(NPN)] (2) by reaction with iPrOH in the presence of a strong base, via an observable isopropoxide intermediate [(η6-Cym)Ru(OiPr)(NPN)] (3), or with NaBHEt3 in toluene. Partial conversion also occurs in iPrOH in the absence of base. 2 is stabilized by dihydrogen bonding with isopropyl alcohol, but attempts to isolate it induce isomerization by hydride migration to a ring CH position to yield a 16-electron cyclohexadienyl derivative [η5-p-C6H5(Me)(iPr)Ru(NPN)], which has been crystallographically characterized as a disordered mixture of two regioisomers (4/4′). Complex 2 is able to release H2 upon treatment with medium strength proton donors (fluorinated alcohols), but also slowly with iPrOH. 2 is an active catalyst for the transfer hydrogenation of acetophenone to phenylethanol in isopropyl alcohol. The catalytic transformation is first order in acetophenone and first order in catalyst, with k = 117 ± 10 m–1 h–1 at 40 °C. The temperature dependence of the rate constant (25–80 °C) gave the activation parameters ΔH‡ = 9.6 ± 1.3 kcal mol–1 and ΔS‡ = –31 ± 4 cal mol–1 K–1. DFT calculations have validated the slow isomerization of 2 to 4/4′ (high energy TS), the preference of the cyclohexadienyl system for 4/4′ relative to the other isomers 4Me and 4iPr, where the hydride has migrated to the CMe or CiPr position, and suggest that the hydrogen transfer mechanism involves outer sphere hydride transfer to the ketone substrate with H-bonding assistance of isopropyl alcohol to yield a σ complex intermediate [(η6-Cym)Ru+(NPN)H-C(Me)(Ph)O–]