Michel Ephritikhine

Recycling of Carbon and Silicon Wastes: Room Temperature Formylation of N–H Bonds Using Carbon Dioxide and Polymethylhydrosiloxane

A highly active organocatalytic system based on N-heterocyclic carbenes has been designed for the formylation of N-H bonds in a large variety of nitrogen molecules and heterocycles, using two chemical wastes: CO(2) and polymethylhydrosiloxane (PMHS).

The U═C Double Bond: Synthesis and Study of Uranium Nucleophilic Carbene Complexes

Treatment of U(BH(4))(4) with 1 or 3 equiv of Li(2)(SCS) x 1.5 Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH(4))(3)](2) (4) and U(mu-SCS)(3)[Li(Et(2)O)](2) (6), respectively [SCS = (Ph(2)P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH(4))(2)(THF)(2) (5). The multiple bond character of the uranium-carbon bond was first revealed by the X-ray crystal structures of the three complexes. The U=C bond in these complexes present a nucleophilic character, as shown by their reaction with a carbonyl derivative. Finally, DFT calculations prove the involvement of both 5f and 6d orbitals in both the sigma and the pi U-C bonds.

Exploring the uranyl organometallic chemistry: from single to double uranium-carbon bonds.

Uranyl organometallic complexes featuring uranium(VI)-carbon single and double bonds have been obtained from uranyl UO(2)X(2) precursors by avoiding reduction of the metal center. X-ray diffraction and density functional theory analyses of these complexes showed that the U-C and U=C bonds are polarized toward the nucleophilic carbon.

Complete Catalytic Deoxygenation of CO2 into Formamidine Derivatives

Because fossil resources are a limited feedstock and their extensive use results in the problematic accumulation of CO2 in the atmosphere, the organic-chemical industry will face important challenges over the coming few decades to circumvent the use of raw fossil materials. In particular, the fuel, petrochemical, and fine-chemicals industries have to find alternative feedstocks and carbon-free energy sources to embrace sustainability. In this regard, CO2 has been proposed as an “energy vector” for renewable energies, as a solution for hydrogen storage, and as a C1 building block for the synthesis of fine chemicals. 6] Yet, as a waste compound, CO2 is thermodynamically and kinetically difficult to transform and research efforts are still needed to promote shifts in technology in the chemical industry. Among the challenges that are associated with CO2 transformation, we must acknowledge that, despite recent progress, the scope of chemical functions that are available from CO2 is still very limited and mostly consists of molecules in which at least one C O bond from CO2 is retained. 6] In fact, the only catalytic reaction that results in the complete deoxygenation of CO2 is its reduction into methane by hydrogenation, hydrosilylation, or electrochemical methods. Interestingly, Wehmschulte and co-workers recently observed that toluene and diphenylmethane could be obtained as side-products in the silylium-catalyzed hydrosilylation of CO2 into methane in the presence of benzene. To utilize CO2 as a “true” C1 building block and to prepare a wide spectrum of chemicals, catalytic reactions that are able to promote the complete deoxygenation of CO2 with the complete reconstruction of the carbon valence sphere are required (Scheme 1). Herein, we report the first solution to tackling this problem by using the cascade reductive functionalization of CO2 into benzimidazoles, quinazolinones, formamidines, and their derivatives. We recently reported an organocatalytic formylation reaction of N H bonds by using CO2 and hydrosilanes to yield formamides. To substitute the C=O bond in the formamide derivative and achieve complete deoxygenation, we reasoned that the amide function could be reacted in a cascade reaction with a nucleophile (Scheme 1), such as an amine. The formylation step was efficiently catalyzed by N-heterocyclic carbenes (NHCs), which were found to be efficient at room temperature for the conversion of a large scope of amines, anilines, imines, and N heterocycles. This reaction was mild, robust, and selective; thus, it offered a good starting point for the development of new cascade reactions. Alternatively, nitrogen bases, such 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), were also active catalysts in this reaction, but at higher temperatures (100 8C). By using a primary amine as a nucleophile, the condensation step with a formamide is known to be thermally available without needing to resort to catalysts. However, hard drying agents, such as phosphorus oxychloride, trifluoroacetic anhydride, and thionyl chloride, are typically required to promote this reaction. To avoid the use of such additives, which increase waste formation, we investigated the reactivity of a diamine, o-phenylene diamine (1 a), in the presence of CO2 and hydrosilanes, so as to favor an intramolecular condensation reaction (Table 1). By using 5.0 mol % of IPr in the presence of CO2 (2 bar) and 1 equivalent of phenylsilane, compound 1 a was converted in high yield into its formyl and N,N’-bisformyl derivatives (compounds 2 a (31 %) and 3 a (38 %) respectively) after 24 h at 25 8C (Table 1, entry 5). To our delight, a significant amount (16 %) of the desired benzimidazole (4 a) was also observed in the reaction mixture. This reaction demonstrated that the complete deoxygenation product (4 a) was available under our reaction conditions. However, the observed selectivity indicates the high rate of the formylation reaction in the presence of PhSiH3. Because compound 3 a is unreactive towards condensation, a less-reactive silane, that is, poly(methylhydrosiloxane) (PMHS), 9] was employed to avoid the formylation of both amine functions. By using 3 equivalents of PMHS under similar reaction conditions (Table 1, entry 6), monoformyl derivative 2 a was formed as the major compound (42 % yield) and compounds 3 a and 4 a were formed as sideproducts (in 20 % and 5 % yield, respectively). Therefore, the condensation step appears to be rate determining in this cascade strategy. As a consequence, raising the operating temper[a] Dr. O. Jacquet, C. Das Neves Gomes, Dr. M. Ephritikhine, Dr. T. Cantat CEA, IRAMIS, SIS2M, CNRS UMR 3299 91191 Gif-sur-Yvette (France) Fax: (+ 33) 1-6908-6640 E-mail : thibault.cantat@cea.fr Homepage: http ://iramis.cea.fr/Pisp/thibault.cantat/index.htm Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200732. It includes a detailed description of the experimental and spectroscopic results. Scheme 1. Principles of our approach.

Solution, Solid State, and Film Properties of a Structurally Characterized Highly Luminescent Molecular Europium Plastic Material Excitable with Visible Light

The synthesis and X-ray crystal structure of the ligand L (4,7-dicarbazol-9-yl-[1,10]-phenanthroline) are reported, as well as those of the molecular complex, [Eu(tta)(3)(L)] (1), (tta = 2-thenoyl trifluoroacetylacetonate). Their photophysical properties have been investigated both in solution and in the solid state. It was shown that the ligands used for designing 1 are well-suited for sensitizing the Eu(III) ion emission, thanks to a favorable position of the triplet state as investigated in the Gd(III) complex [Gd(tta)(3)(L)], (2). The low local symmetry of the Eu(III) ion shown by the X-ray crystal structure of 1 is also revealed by luminescence spectroscopy. Because of interesting volatility and solubility properties, 1 is shown to behave as a real molecular material that can be processed both by thermal evaporation and from solution. When doped in poly(methylmethacrylate) (PMMA), 1 forms air-stable and highly red-emitting plastic materials that can be excited in a wide range of wavelengths from the UV to the visible part of the electromagnetic spectrum (250-560 nm). Absolute quantum yields of 80% have been obtained for films comprising 1-3% of 1. Ellipsometry measurements have been introduced to gain information on physical data of 1. They have been performed on thin films of 1 deposited by thermal evaporation and gave access to the refractive index, n, and the absorption coefficient, k, as a function of the wavelength. A value of 1.70 has been found for n at 633 nm. These thin films also show interesting air-stability.

The affinity and selectivity of terdentate nitrogen ligands towards trivalent lanthanide and uranium ions viewed from the crystal structures of the 1 ∶ 3 complexes

Treatment of LnI3 (Ln = La, Ce) or [UI3(py)4] with 3 equivalents of terpy in acetonitrile gave the tris(terpy) complexes [M(terpy)3]I3. Addition of 3 equivalents of Rbtp (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine) to MX3 (X = I or OSO2CF3) in pyridine or acetonitrile afforded the tris(Rbtp) compounds [M(Rbtp)3]X3. By comparison with terpy, the Rbtp ligand has a better affinity for the 4f and 5f ions and is more selective for U(III) than for Ce(III) or La(III). This trend has been revealed by 1H NMR competition experiments and X-ray crystallographic studies which show that in the [M(terpy)3]3+ and [M(Rbtp)3]3+ cations, the M–N(Rbtp) bond lengths are shorter than the M–N(terpy) bond lengths, and the U–N bond lengths are shorter than the corresponding Ce–N or La–N bond distances.

NEW ADVANCES IN THE CHEMISTRY OF URANIUM AMIDE COMPOUNDS

Abstract The chloroamide complexes U(NEt 2 ) 4− x Cl x ( x =1, 2) were obtained by comproportionation of UCl 4 and U(NEt 2 ) 4 . The novel protonolysis reaction of a metal–amide bond with an acidic ammonium salt proved to be an efficient and convenient synthesis of cationic compounds. Thus were synthesized a series of metallo-organic and organometallic uranium cations in the oxidation states +3, +4, +5. The cationic amide compounds were valuable precursors of new derivatives, as they reacted with anionic reagents, acidic substrates and unsaturated molecules to give the addition, substitution and insertion products; in particular, such reactions were useful for the synthesis of monocyclooctatetraene uranium compounds. The dialkyl amide ligand was found able to stabilize the +5 oxidation state of uranium; neutral and cationic uranium(V) complexes were obtained by oxidation of their corresponding anionic and neutral U(IV) precursors.

Easy access to stable pentavalent uranyl complexes

Reaction of UO2I2(THF)3 with 1 molar equivalent of KC5R5 (R = H, Me) in pyridine led to the uranyl(V) compound {[UO2(Py)5][KI2(Py)2]}(infinity), which is an infinite 1D polymer in its crystalline form; the UO2X(THF)n (X = I, OSO2CF3) complexes were obtained by reduction of their U(VI) parents with TlC5H5 or KC5R5 in THF.

Synthesis and crystal structure of the oxo-bridged bimetallic organouranium complex [(Me3SiC5H4)3U]2[μ-O]

Abstract The compound (Me 3 SiC 5 H 4 ) 3 U (I) reacts with CO 2 or N 2 O to give [(Me 3 SiC 5 H 4 ) 3 U] 2 [μ-O] (II), the crystal structure of which reveals presence of a linear U-O-U bridge with U-O distances of 2.1053 (2) A.

Dehydrocoupling reactions of amines with silanes catalyzed by [(Et2N)3U][BPh4]

Abstract Dehydrocoupling reactions of primary amines RNH2 with PhSiH3 were catalyzed by [(Et2N)3U][BPh4] to give the corresponding aminosilanes PhSiH3−n(NHR)n (n=1–3), the relative yields of the products were found to be dependent on the experimental conditions and on the nature of R. For a primary silane (PhSiH3), the reactivity of RNH2 follows the order primary>secondary>tertiary. Similar dehydrocoupling reactions using secondary amines with secondary silanes were found to be less reactive. Homodehydrocoupling of the silane was found not to be a competing reaction at room temperature. The hydride [(RNH)2UH][BPh4], which is plausibly formed in the reaction of [(RNH)3U][BPh4] with PhSiH3 is a likely intermediate in the catalytic cycle.