Intrinsic dinitrogen activation at bare metal atoms

There is ongoing interest in metal complexes which bind dinitrogen and facilitate either its reduction or oxidation under mild conditions. In nature, the enzyme nitrogenase catalyzes this process, and dinitrogen fixation occurs under mild and ambient conditions at a metal-sulfur cluster in the center of the MoFe protein, but the mechanism of this process remains largely unknown. In the last few years, new important discoveries have been made in this field. In this review are discussed recent findings on the interaction of N(2) with metal atoms and metal-atom dimers from all groups of the periodic table as provided by gas-phase as well as matrix-isolation experiments. Intrinsic dinitrogen activation at such bare metal atoms is then related to corresponding processes at complexes, clusters, and surfaces.     

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis,Structure, and Bonding

Electron‐deficient small boron rings are unique in their formation of σ‐ and π‐delocalized electron systems as well as the avoidance of “classical” structures with two‐center‐two‐electron (2c,2e) bonds. These rings are tolerant of several skeletal electron numbers, which makes their redox chemistry highly interesting. In the past few decades, a range of stable compounds have been synthesized with various electron numbers in their B₃ and B₄ cores. The electronic structures were evaluated by quantum‐chemical calculations. On the other hand, the chemistry of these rings is still very much underdeveloped, being generally limited to the protonation and redox reactions of individual systems. The linkage of several B₃ and/or B₄ ring systems should give compounds with attractive electronic properties, thus leading the way to novel boron‐based materials. By summarizing important experimental and theoretical results, this Review intends to provide the basis for the exploration of the chemistry of these rings and, in particular, their integration into larger molecular architectures.     

Testing Lorentz invariance and CPT conservation with NuMI neutrinos in the MINOS near detector

A search for a sidereal modulation in the MINOS near detector neutrino data was performed. If present, this signature could be a consequence of Lorentz and CPT violation as predicted by the effective field theory called the standard-model extension. No evidence for a sidereal signal in the data set was found, implying that there is no significant change in neutrino propagation that depends on the direction of the neutrino beam in a sun-centered inertial frame. Upper limits on the magnitudes of the Lorentz and CPT violating terms in the standard-model extension lie between 10(-4) and 10(-2) of the maximum expected, assuming a suppression of these signatures by a factor of 10(-17).     

Access to the Bis‐benzene Cobalt(I) Sandwich Cation and its Derivatives: Synthons for a “Naked” Cobalt(I) Source?

The synthesis and structural characterization of the hitherto unknown parent Co(bz)₂⁺ (bz=benzene) complex and several of its derivatives are described. Their synthesis starts either from a CoCO₅⁺ salt, or directly from Co₂(CO)₈ and a Ag⁺ salt. Stability and solubility of these complexes was achieved by using the weakly coordinating anions (WCAs) [Al(OR^F)₄]^? and [F{Al(OR^F)₃}₂]^? {R^F=C(CF₃)₃} and the solvent ortho‐difluorobenzene (o‐DFB). The magnetic properties of Co(bz)₂⁺ were measured and compared in the condensed and gas phases. The weakly bound Co(o‐dfb)₂⁺ salts are of particular interest for the preparation of further Co^I salts, for example, the structurally characterized low‐coordinate 12 valence electron Co(P^tBu₃)₂⁺ and Co(NHC)₂⁺ salts.     

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde

Oxymethylene dimethyl ethers (OME_n; CH₃(‐OCH₂‐)_nO‐CH₃, n=3–5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot‐free combustion. Herein a novel anhydrous OME_n synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OME_n at temperatures of 25–30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OME_n emanating from CO₂ and H₂.     

Mono- and diprotonation of the superbasic bisguanidine 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) and Pt II and Pt IV complexes of chelating bisguanidines and guanidinates

New Pt complexes of chelating bisguanidines and guanidinate ligands were synthesized and characterized. 1,2-Bis(N,N,N',N'-tetramethylguanidino)benzene (btmgb) was used as a neutral chelating bisguanidine ligand, and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate (hpp(-)) as a guanidinate ligand. The salts [btmgbH](+)[HOB(C(6)F(5))(3)](-) and [btmgbH(2)]Cl(2) and the complexes [(btmgb)PtCl(2)], [(btmgb)PtCl(dmso)](+)[PtCl(3)(dmso)](-), and [(btmgb)PtCl(dmso)](+)[Cl(-)] were synthesized and characterized. In the [btmgbH](+) cation the proton is bound to only one N atom. In the other complexes, both imine N atoms are coordinated to the Pt(II), thus adopting a eta(2)-coordinational mode. The hpp(-) anion, which usually prefers a bridging binding mode in dinuclear complexes, is eta(2)-coordinated in the Pt(IV) complex [(eta(2)-hpp)(hppH)PtCl(2){N(H)C(O)CH(3)}], which is formed (in low yield) by reaction between cis-[(hppH)(2)PtCl(2)] and H(2)O(2) in CH(3)CN.     

Synthese und Einkristallstrukturanalyse von Bis(benzyltrimethylammonium)fullerid-Ammoniakat; (BzlNMe3)2C60 · 3 NH3

Synthesis and Single Crystal Structure Analysis of Bis(benzyltrimethylammonium)fulleride Ammonia 1/3, (BzlNMe₃)₂C₆₀ · 3 NH₃ The title compound has been prepared from K₂C₆₀ by ion exchange of potassium for benzyltrimethylammonium cations in liquid ammonia. X-ray single crystal structure analysis reveals highly ordered fulleride ions forming a layer-like arrangement with short inter-fullerene distances. The anionic fulleride layers are separated by layers of benzyltrimethylammonium cations and ammonia.     

Herstellung organischer Dünnstschichten

In this paper we present different experiments describing the fabrication and characterisation of self-assembled monolayers of organothiols and also discuss some of the most important applications of these systems. The reader may practise the fabrication and characterisation of self-assembled monolayers with different endgroups by adsorption of CH₃- and Oh-terminated alkanethiols on copper-coins (1 or 2 Pfenningcoins). Then patterned self-assembled monolayers of CH₃- and OH-terminated alkanethiols are produced by applying the microcontact printing technique. When these gratings are wet with water-e.g. by breathing into the surfaces-the water adsorbs onto the hydrophilic OH-terminated areas but not on the hydrophobic CH₃-terminated regions. Illumination with a laser then produces bright diffraction spots which disappear when the water evaporates. Finally, we briefly discuss applications of the self-assembled ultrathin films as sensor-devices and as substrates for CVD (chemical vapour deposition).