Olaf Walter

Catalysis of allylic substitutions by Pd complexes of oxazolines containing an additional P, S, or Se Center. X-ray crystal structures and solution structures of chiral π-allyl palladium complexes of phosphinoaryloxazolines

Allylic alkylations with Pd complexes of chiral oxazolines with an additional donor P, S, or Se center are reported. Crystal and solution structures of palladium π-allyl complexes of phosphinoaryloxazolines were determined by X-ray crystallography and cross relaxation experiments, respectively. From the results conclusions concerning the steric course of allylic substitutions are drawn.

Magnetic Memory Effect in a Transuranic Mononuclear Complex

Molecular nanomagnets that display magnetic bistability are the subject of intensive investigation due to their unique potential in ultrahigh-density memory components and spintronic devices. So far, the best practical realization of such single-molecule magnets (SMMs) are polymetallic transition-metal complexes with strong intramolecular exchange coupling, giving rise to a high-spin ground state and negligible intercluster interactions. However, 3d metals are restricted by their comparatively low anisotropy, and SMMs with better performance could be produced by exploiting the higher single-ion anisotropy typical of felectron ions. This possibility has been practically demonstrated by Ishikawa et al., who discovered that mononuclear rare earth metal bis-phthalocyanine compounds (Pc2RE) display magnetic hysteresis under favorable conditions. On these grounds, the use of actinides in molecular magnetism appears timely, and indeed slow relaxation effects have recently been reported in a mononuclear uranium-based molecule. Future SMMs displaying magnetic hysteresis could benefit from the fact that, whilst the 5f electron shell can remain relatively well localized, its larger radial extension with respect to the 4f shell can result both in an increased ligand-field potential (and therefore a higher anisotropy energy barrier) and in the possibility to trigger a sizeable exchange coupling in polynuclear complexes, usually precluded to trivalent rare earth metal ions. Moreover, discrete molecules based on 5f ions should allow much greater understanding of the peculiar behavior observed in actinide materials, including multipolar superexchange coupling. Recently, we obtained evidence that a neptunium trimetallic compound displays slow magnetic relaxation and superexchange interaction; nevertheless, we were unable to find any signs of hysteresis in the measured magnetization curves. Here we report the first observation of such low-temperature magnetic memory effects in another transuranic molecular complex, namely, bis(cyclooctatetraenyl)neptunium(IV), commonly known as neptunocene [Np(COT)2] (COT= C8H8 2 ), which was first described in 1970 and belongs to the whole actinocene row. The molecule has a single Np ion between two planar COT rings in a sandwich structure (Figure 1) with D8h symmetry. [9] The degeneracy of the lowest

Chirale tripodliganden : Die Eintopfreaktion MeC(CH2PPh2)3→MeC(CH2P(Ph)(R))3; Zwischenstufen, diastereoselektive Kontrolle und Komplexchemie

Abstract The tripod ligand H 3 CC(CH 2 PPh 2 ) 3 , 1 , reacts with lithium metal to produce H 3 CC(CH 2 PPhLi) 3 , 2 , in good yields. Compound 2 crystallizes in the form of 2 · 4 THF·MeN(CH 2 CH 2 NMe 2 ) 2 . The crystal structure of this adduct shows bridging as well as terminal phosphorous-coordination of lithium. Compound 2 reacts with electrophiles RX to give H 3 CC(CH 2 P(Ph)(R)) 3 , 3 (R = H, Me, Et, i Pr, CH 2 Ph, 3a–3e ). The transformation 1 → 2 → 3 can be performed in a one-pot reaction. While the chiral compounds 3 may be characterized as such, their reaction with (CH 3 CN) 3 Mo(CO) 3 yields the easy-to-characterize coordination compounds H 3 CC(CH 2 P(Ph)(R)) 3 Mo(CO)3, 5 . NMR analysis of 3 and 5 shows that from the two diastereomeric forms of 3 (the enantiomeric pair SSR / RRS and the pair SSS / RRR ) only the SSR / RRS -diastereomer is formed with R = CH 2 Ph ( 3e , 5e ). In the other cases (R = H, Me, Et, i Pr) a statistical 3:1 mixture of the two diastereomers is formed. These findings are further corroborated by X-ray analyses of H 3 CC(CH 2 P(Ph)(Et)) 3 Mo(CO) 3 , 5c , and H 3 CC(CH 2 P (Ph)(CH 2 Ph)) 3 Mo(CO) 3 , 5e . The remarkable facts reported in this paper are the ease with which the chiral tripod ligands H 3 CC(CH 2 P(Ph)(R)) 3 , 3 , are prepared, and the evidence that their formation may well involve diastereoselective control.

Insertion reaction of carbon dioxide into Sn–OR bond. Synthesis, structure and DFT calculations of di- and tetranuclear isopropylcarbonato tin(IV) complexes

The reaction of carbon dioxide with the stannane nBu2Sn(OiPr)2 and distannoxane [nBu2(iPrO)Sn]2O leads to the selective insertion into one Sn-OiPr bond generating the corresponding nBu2Sn(OiPr)(OCO2(i)Pr) and nBu2(iPrO)SnOSn(OCO2(i)Pr)nBu2 species. Both compounds are characterised by multinuclear NMR, FT-IR and single-crystal X-ray crystallography. In the solid state, they adopt a dimeric arrangement with bridging isopropoxy and terminal isopropylcarbonato ligands. The X-ray crystal structure of the dinuclear stannane shows that the Sn2O2 ring and the two Sn-OCO2C fragments are nearby coplanar. The same holds for the ladder-type tetranuclear distannoxane. The dimeric structures are also evidenced by solution NMR in non-coordinating solvents. Interestingly, the assignment of the exo and endo tin resonances of the dimeric distannoxane is unambiguous using a labeled 13CO2 experiment. The stability of the dimeric association has been probed in the stannane series on the basis of DFT calculations.

Reactivity towards dioxygen of a copper(I) complex of tris(2-benzylaminoethyl)amine

Abstract The reaction of dioxygen with the copper(I) Bz 3 tren complex (Bz 3 tren=tris(2-benzylaminoethyl)amine) complex has been investigated using low temperature stopped-flow techniques. The formation of a superoxo as well as a peroxo complex as intermediates was detected spectroscopically. The copper(II) complexes [Cu(Bz 3 tren)H 2 O](ClO 4 ) 2 and [Cu(Bz 3 tren)Cl]Cl were synthesized and structurally characterized. Both complexes react with dioxygen in solution and formation of benzaldehyde was observed.

Synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by an easy-to-handle ionic iron(III) complex

We report the successful utilization of monometallic, ionic iron(II)- and iron(III)-N2O2-ligand-systems as highly active homogeneous catalysts for the conversion of CO2 with different epoxides to cyclic carbonates. The catalytic tests were performed using propylene oxide (PO) and a range of nine substituted epoxides. Terminal monosubstituted oxides react quantitatively.

Syntheses, Structures, and Properties of Copper(II) Complexes of Bis(2-pyridylmethyl) Derivatives of o-, m-, and p-Phenylenediamine and Aniline

Copper(II) complexes of the ligand 1,n-bis[bis(2-pyridylmethyl)amino]benzene with n = 2-4 (1,n-tpbd) and its mononuclear derivative bis(2-pyridylmethyl)aniline (phbpa) were synthesized and structurally characterized. Magnetic measurements and DFT calculations were performed on [CuCl2(phbpa)], [Cu2Cl4(1,3-tpbd)], [(Cu2Cl2(ClO4)(1,3-tpbd))Cl(Cu2Cl2(OH2)(1,3-tpbd))](ClO4)2, and [Cu2(OH2)2(S2O6)(1,3-tpbd)]S2O6, and the exchange-polarization mechanism was successfully demonstrated.

Non‐aqueous Synthesis of Isotropic and Anisotropic Actinide Oxide Nanocrystals

The huge interest of the scientific community in the controlled synthesis, structural characterization and assembly into 2and 3-dimensional architectures of nano-objects as well as investigations of their corresponding chemical and physical properties cannot be denied anymore. Within the past two decades, it has been shown that size reduction means more than simply making things smaller. Indeed, size decreasing (as well as shape controlling) is a powerful way to tune materials properties (magnetic, electronic, optical, catalytic, etc.). Whereas nanoscience is a very active field when one considers stable elements, it is still in its infancy when dealing with radioactive actinides. Actinide compounds are important in the nuclear industry and actinide-based nano-objects could be used as new building blocks for the preparation of innovative nuclear fuels or as model systems to study the migration of radionuclides in the environment (e.g., in nuclear waste disposal). The actinide series is also characterized by the emergence of 5f electrons in the valence shell. The behaviour of the 5f electrons determines the solid-sate properties of the actinides and their compounds. Compared to the stable elements, questions related to size and shape effects on the physical and chemical properties of actinide compounds are still open and should find their way into the nanoscience. Accordingly, our main goal is dedicated to the controlled synthesis, the structural characterization and the investigation of the properties of actinide-based nano-objects. Here, we report on the controlled synthesis of uranium oxide and thorium oxide nanocrystals (NCs) by a non-aqueous approach. The obtained NCs have been characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results of this study therefore present an important step for moving to the preparation of transuranium oxide NCs (e.g., NpO2, PuO2). Uranium and thorium oxide NCs were synthesized by the so-called “heating-up” method by using standard air-free techniques. Uranyl acetylacetonate (UO2ACHTUNGTRENNUNG(acac)2) or thorium acetylacetonate (ThACHTUNGTRENNUNG(acac)4) are introduced in a degassed mixture of dibenzyl ether (BnOBn) with different concentrations of stabilizing agents, like oleic acid (OA), oleylACHTUNGTRENNUNGamine (OAm), trioctylamine (N ACHTUNGTRENNUNG(Oct)3) and trioctylphosphine oxide (OP ACHTUNGTRENNUNG(Oct)3). The resulting mixtures are then heated up to 280 8C. After being cooled to room temperature, the NCs are precipitated with ethanol followed by centrifugation and re-dispersion in toluene. Surprisingly, the experimental conditions well-suited for the formation of uranium oxide NCs cannot be applied when considering the formation of thorium oxide NCs. The modification of the reactivity (for a given organic system) as a function of the nature of the actinide precursor and/or the actinide centre seems to be essential when taking into account the synthesis of actinide oxide NCs. Because of these differences in the reactivity of uranium and thorium precursors, different solvent compositions were tested in order to find the best reaction conditions to obtain well defined NCs. A black precipitate can be isolated from the reaction of UO2ACHTUNGTRENNUNG(acac)2 in a mixture of BnOBn/OA/OAm. The PXRD data of the as-prepared compound along with the corresponding Rietveld refinement are presented in Figure 1 a. The PXRD pattern exhibits Bragg reflections characteristic of the fluorite structure (space group Fm-3m). The experimental PXRD pattern was calculated by using the bulk structure of uranium dioxide (UO2). The detailed results of the Rietveld refinement are given in the Supporting Information. The peak broadening is the result of the small size of the coherent domains (the crystallites), which has been estimated with the fundamental approach to be 4.5 nm. Under the same experimental conditions (i.e., BnOBn/ OA/OAm), the reaction of ThACHTUNGTRENNUNG(acac)4 did not give rise to the formation of thorium-based NCs. Indeed, in the presence of [a] Dr. D. Hudry, Dr. C. Apostolidis, Dr. O. Walter, Dr. T. Gouder European Commission: Joint Research Center Institute for Transuranium Elements, P. O. Box 2340 76125 Karlsruhe (Germany) Fax: (+49) 7247-951-599 E-mail : damien.hudry@ec.europa.eu damien.hudry@gmail.com [b] Dr. E. Courtois, Dr. C. K bel Karlsruhe Institute of Technology, Institute of Nanotechnology Hermann-von-Helmholtz-Platz 1 76344 Eggenstein–Leopoldshafen (Germany) [c] Dr. C. K bel Karlsruhe Nano Micro Facility, Hermann-von-Helmholtz-Platz 1 76344 Eggenstein–Leopoldshafen (Germany) [d] Dr. D. Meyer Institut de Chimie S parative de Marcoule, UMR 5257 BP 17171, 30207 Bagnols sur C ze Cedex (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200513.

Controlled Synthesis of Thorium and Uranium Oxide Nanocrystals

Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well-defined actinide-based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non-aqueous surfactant-assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra-small diameters of 1 nm) of thorium oxide were synthesised.

Thorium/uranium mixed oxide nanocrystals: Synthesis, structural characterization and magnetic properties

One of the primary aims of the actinide community within nanoscience is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects (e.g. nanocrystals) are necessary. Hence, a “library” dedicated to the preparation of various actinidebased nanoscale building blocks is currently being developed. Nanoscale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nanocrystals (both for thorium and uranium, and recently extended to neptunium and plutonium). In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nanocrystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate (together with additional capping agents) into benzyl ether can be used to synthesize thorium/uranium mixed oxide nanocrystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium:uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nanocrystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nanocrystals of non-magnetic oxides as recently claimed in the literature.