Chemistry - A European Journal

Gold nanotube membranes are prepared by electroless deposition of Au within the cylindrical and monodisperse pores of a nanopore polycarbonate template membrane (see scheme). This electroless deposition allows for precise control of the nanotube inside diameter, and we have prepared Au nanotubes that have inside diameters of molecular dimensions (<1 nm). This new class of membranes is utilized for chemical separations and sensing.

“So you think your process is green, how do you know?” We propose a simple, easy to use, environmental performance metric to evaluate chemical syntheses and reactions on a laboratory scale in a very practical approach using EATOS (environmental assessment tool for organic syntheses). This helps to weigh up the options (see diagram).

Coordination polymers with two-dimensional frameworks with a double-edged axe-shaped motif have been synthesized from reactions of cobalt(II) thiocyanate with N-(3-pyridyl)isonicotinamide (3-pia) or N-(3-pyridyl)nicotinamide (3-pna) (see figure). Crystal-to-crystal transformation accompanying inclusion of guest molecules by dynamically switching amide groups in the structure has been found.

Extended tetrathiafulvalenes containing varying numbers of acetylene units in the spacer are readily synthesized from mono- and diacetylenic dithiafulvene building blocks. These large π-systems are strong chromophores and exhibit good third-order nonlinear optical properties. The electrochemical behavior was influenced by both structural changes in the spacer and by lateral functionalization (R′).

Presently, we are far from understanding the rules governing the generation of [2×2] grids, tetrahedra, or triangles from basically very similar ligands and hexacoordinating transition metal ions. [{Fe₃O(L)₂(OAc)₄}₂O] (1), for instance, is generated in a one-pot reaction in 45 % yield.

Carbocycles are formed by the intramolecular palladium-catalyzed coupling of allylstannanes or allylsilanes with allyl carboxylates by formation of a CC bond between the C-3 termini of the allyl ligands of bis(η³-allyl)palladium complexes (see scheme).

Fast interconversion of Tröger's base and a monobenzylated Tröger's Base derivative has been observed under acidic conditions by dynamic electrokinetic chromatography followed by direct calculation and computer simulation of the rate constants. The enantiomerization barrier is considerably lowered by the introduction of a permanent positive charge; this is attributed to the interconversion mechanism occurring via an iminium transition state (see scheme).

Hydrogen bonds in control! Investigation of the transmission of long-range magnetic interactions through hydrogen bonds has been carried out for two different benzoic acid derivatives which bear either a tert-butyl nitroxide (NOA) or a polychlorotriphenylmethyl (PTMA) radical moiety. The synthesis of these radicals and extensive ESR and magnetic susceptibility studies on their dimers in solution and in the solid state are described. The results show that magnetic exchange interactions are transmitted efficiently through the hydrogen bonds between the carboxylic groups that form the dimer.

Although one might think that the reaction of ketones with primary or secondary amines should afford the corresponding imines or enamines, the reaction of azetidine-2,3-diones with primary as well as secondary amines, and water is a novel method for the one-step preparation of α-amino acids, α-amino amides and dipeptides (see scheme), in both the racemic and optically pure forms.

The results of a theoretical and mass spectrometric study show that formation of O₃⁺ [Eq. (1)] from the reaction of vibrationally excited O₂⁺(⁴Π_u, ν′) ions with oxygen involves the intermediacy of two isomeric O₄⁺ complexes.

A meaningful comparison of the exchange and double-exchange contributions to the energy separation between the ground S=3/2 and the first excited S=1/2 of the mixed-valence Ni^II–Ni^I species in [Ni₂(napy)₄X₂]⁺ (X=Cl, Br, I) ions has been made possible through DFT calculations. The use of high-frequency EPR spectroscopy together with low-temperature magnetic measurements provided an unambiguous description of the zero-field splitting of the ground S=3/2 state, both in terms of the absolute value and sign, which was successfully related to ligand field parameters. The present investigation shows how the combination of DFT calculations and spectroscopic methods may yield important information in mixed-valence compounds.

A new series of imidazolium cation-based room temperature ionic liquids [C_nO_mmim][X] has been prepared. Their solubility in common solvents, viscosity, solid–liquid phase transition, density and solubility of inorganic salts are investigated.

The structural determination of inclusion compounds derived from a cyclophane host and the three isomers of picoline and lutidine was followed by competition experiments (left) which showed strong concentration-dependent selectivities when the complexes could be assigned to different adduct classes. Selectivities can be explained by a set of favorable hydrogen bonding schemes as outlined for the adduct of 1 with 4-picoline (right).

The direct and site-selective acylation of lysine and ornithine residues in folded four-helix bundles (see scheme) with fumarate 1 provides an automatable route towards multifunctional proteins with tailored functions. The site selectivity is due to the incorporation of lysine/ornithine residues in positions with hydrophobic character.

A regio- and stereoselective sequential insertion of two P-coordinated PPh₂CCR ligands on cis-[M(C₆F₅)₂(PPh₂CCR)(PPh₂CCR′)] (see scheme) into a strong Pt(C₆F₅) bond of the “Pt(C₆F₅)₂” synthon has been observed. The insertion affords formal 14-electron Pt(σ,π-butadienyl) (C₆F₅) fragments, which are easily stabilized by donor molecules, and the first example of an isolable and crystallographically characterized T-shaped 3-coordinated platinum center and some reaction products are also reported.

The upper and lower rims of a [6]cavitand have been selectively derivatized: the upper rim to give the compounds depicted (X=H, Br, CN, OAc, SH, SAc); the lower rim to give a bisketone, bisdiol, and bisacetate. The crystal structures of the diol and bisketone are reported, and a conformational analysis of each cavitand is discussed.

Highly active and stable catalysts for the oxidation of cyclohexane have been prepared by immobilization of cobalt acetate oligomers [py₃Co₃(μ₃-O)(OH)(O₂CCH₃)₅](PF₆) and [py₄Co₂(OH)₂(O₂CCH₃)₃](PF₆) on various carboxy-modified mesoporous silica supports (see scheme). The oxidation of cyclohexane by tert-butyl hydroperoxide (TBHP) in the presence of these catalysts affords the corresponding alcohol and ketone with high selectivity. The course of the catalytic reaction has been studied in detail.

Thallium(I)-induced coupling of 1,8-diaminonaphthalene provides a facile and selective method for the preparation of tetra(amino)perylenes and their derivatives. In their quinoidal form I, they are only weakly emitting dyes and possess photo- and electrochemical properties which set them apart from the established perylene-bis(imides). Their properties as bridging ligands have been examined for compound II, which displays strong electronic coupling of the metal centers through the extended π system of the rigid ligand.

Directed α-epoxidation and easy deprotection of 3-O-PMB epothilone C produce epothilone A in high yields (see scheme). Other key steps include epoxide opening with acetylide, modified Wittig reaction of 2 with a ketone bearing a long chain and Jacobsen's KHR for the preparation of the C1–C6 segment. The methodologies used are useful for the synthesis of epothilones and their analogues.

Complexes of even higher nuclearity may be formed in the equilibrium mixture of monomer 1 and dimer 2, which was obtained by complexation of a trisphenolate ligand with manganese(III) and has been examined by electrochemistry and EPR spectroscopy. The complex 1 is an epoxidation catalyst and features a phenoxy radical in one of the oxidized states.

The accessibility of various solid supports (TentaGel, PEGA 1900, and beaded CPGs) to a range of enzymes was investigated by means of confocal Raman microscopy. It was found that none of the investigated enzymes could enter the polymer matrices of TentaGel. PEGA 1900 was compatible only with the two smallest enzymes, while beaded CPG was successful even with NEP (90 kDa), proving its superiority over other materials in terms of bio-compatibility.

An effective catalytic system for ethylene polymerization has been generated by the activation of simple homoleptic neodymium alkoxides (see f.e. figure) by a dialkylmagnesium. Precipitation of the active species during the reaction course provides a unique heterogeneous catalyst that enables one to achieve solid-gas ethylene polymerization and to prepare efficiently diblock poly(ethylene-co-methyl methacrylate).

Acyclic and cyclic alkenes and alkadienes are readily “dialkylaminocyclopropanated” upon treatment with cyclohexylmagnesium bromide in the presence of methyltitanium triisopropoxide or titanium tetraisopropoxide and an N,N-dialkylformamide (see scheme). The new method provides particularly high yields of diastereomerically pure bicyclic amines such as 6-(dibenzylamino)-3-tert-butoxycarbonyl-3-azabicyclo[3.1.0]hexane and 6-(dibenzylamino)bicyclo[3.1.0]hexane from strained cyclic alkenes (Boc=tert-butyloxycarbonyl).

The ring-opening reaction of 1 with Me₃SnCl affords high yields of a derivative (2) in which a boryl and a stannyl moiety coexist at the peri positions of a naphthalene core. Compound 2 is a useful starting material that can be converted into the heteronuclear B/Ga (3) and B/In (4) bidentate Lewis acids. Structural analysis reveals that 3 and 4 are the first examples of Ga^III and In^III π-arene complexes.

At the nanometer level, matter reveals optical and conducting properties that differ drastically from the respective bulk materials. In this paper we show how dimensions of the materials used as solid supports for fluorescent dyes play a crucial role in the intensity of fluorescence. It has been possible to arrange metal particles of different sizes in ordered two-dimensional patterns with periodicity in the μm range. On such nano-patterned substrates fluorescence could be observed with laser-scanning optical microscopy, whereas on bulk gold the fluorescence was highly quenched.