Angewandte Chemie International Edition

No interaction with the metal center is necessary for the rapid, productive, and stereoselective catalytic hydrogenation of simple ketones when these reactions are carried out in the presence of complexes of general form [RuCl₂(phosphane)₂(1,2-diamine)]. The combined use of a BINAP ligand and a chiral 1,2-diamine allows for asymmetric hydrogenation of a wide range of aromatic, heteroaromatic, and olefinic ketones to the corresponding chiral alcohols with high enantiomeric excess [Eq. (1)]. R=aryl, heteroaryl, alkenyl; R=alkyl; Ar=3,5-(CH₃)₂C₆H₃.

Mimicking nature: The encapsulation of an active site within a protein shell is a well-known structural motif in enzymology. During the last decade considerable advances have been made in using the unique architecture of a dendrimer to shield photo-, electro-, or catalytically active core moieties (see schematic representation). This area of research has led to many new discoveries spanning the design of biological mimics to the construction of optoelectronic devices.

Since their discovery nearly 20 years ago TADDOLs and their derivatives have revealed themselves to be true chiral auxiliary systems. Compounds of this type are accessible from tartaric acid with an almost unlimited degree of structural variety. They serve not only as homogeneous and solid phase bound chiral reagents and ligands for stoichiometric and catalytic applications, but also assist in creating cholesteric phases and host lattices capable of distinguishing between enantiomeric inclusions or facilitating enantioselective solid-phase reactions. The availability of over 120 crystal structures (see the overlays in the picture) makes it possible to discuss mechanistic models for courses of the various reactions.

The evaluation of the publications in Angewandte Chemie as well as the journal as a whole, in terms of the numbers of citations in the Science Citation Index (SCI) and the Journal Impact Factor (JIF), are studied with regard to errors resulting from the publication of two editions of the journal.

At a cationic ketene iridium(I) complex a fundamentally important reaction for organometallic chemistry, namely the metal-assisted reversible cleavage of a C−C double bond [Eq. (1)], has been illustrated for the first time. This study will probably initiate a reinvestigation of the elementary steps of the Fischer–Tropsch synthesis with the aim to find more appropriate catalysts for the selective generation of oxygen-containing products.

A danger to cryptography is not yet present but theoretical concepts of quantum-information processing can be realized experimentally using the methods of NMR spectroscopy and these thereby usher in the quantum computer. The design and synthesis of compounds suitable to form the molecular basis of larger NMR quantum computers is an interesting, but far from trivial, challenge.

The highest nuclearity cyclic structure for the 3d metals is the Ni₂₄ cage reported. It can be described as an octamer of trinuclear units (shown schematically), held together by metal–ligand bonds and a large number of hydrogen bonds.

No elaborate syntheses are required to generate colorimetric anion sensors. Rather, many commercially available chromophores (dyes) with built-in hydrogen bond donor sites have been found to act as “off-the-shelf” anion indicators (see scheme). These species allow for the so-called naked eye detection of fluoride, chloride, and phosphate anions under a range of conditions.

Enough mechanical stiffness that the metal centers can no longer racemize is provided by the connection of four labile metal centers (Al^III, Ga^III, In^III, Fe^III) and six achiral bis-catecholate ligands in a rigid tetrahedral assembly (see picture). The resolution and unprecedented kinetic stability of such a chiral supramolecular assembly is reported here for the first time.

Useful catalytic BOXes: Chiral bisoxazoline (BOX)/Lewis acid complexes can catalyze highly enantioselective Friedel–Crafts alkylation reactions. The new reaction (see scheme) is successful with both aromatic and heteroaromatic compounds and with a wide range of β,γ-unsaturated α-ketoesters (R¹ = alkyl, aryl, or a protected alcohol). Products are formed with up to >99 % ee.

Libraries of low molecular weight aza-RGD mimetics were synthesized according to the split method and evaluated by on-bead screening with a soluble integrine receptor. No coding was required because the biologically active mimetics could be identified using MSⁿ after photochemical cleavage from the stained beads (see picture). New α_vβ₃ antagonists were found by this approach.

In oxygen-containing media the electrochemical regeneration of NADH is easier than expected, such that the regeneration procedure can even be applied to NAD(P)H-dependent monooxygenases (see scheme).

Micropatterned lipid bilayers have been created on solid supports by using lithographic polymerization of a diacetylene lipid (see picture). The domains of polymerized (light) serve, after removal of the monomers, as a two-dimensional master structure for the incorporation of biologically relevant lipid bilayer membranes.

Highly strained and highly explosive: The highly strained heterocycles 3 are generated by thermolysis or photolysis of the azides 2 which resulted from ring cleavage of cyclobutenes 1. Even at −25°C, the aromatization 3→4 occurs. On photochemical or silver-salt induced reactions, 3 can also be transformed into pyrimidines.

A breakthrough in the asymmetric isomerization of 4,7-dihydro-1,3-dioxepins 1 was achieved by using DuPHOS-modified dihalogenonickel complexes such as 4 as catalyst precursors. The absolute configurations of the isomerization products were determined by transforming 2 into 2-hydroxy-γ-butyrolactone 3 and 1,2,4-butanetriol through a new oxidation-ring contraction sequence. The relative configuration of the oxidation product 5 was established by crystal structure analysis.

Surprising symmetry, surprising synthesis: Dicyclopropyldiethenylmethane (2), prepared from dicyclopropylketone (1) in several steps, was successfully cyclopropanated with a large excess of diazomethane in the presence of palladium(II) acetate yielding the structurally interesting tetracyclopropylmethane (3; 92 % yield). Upon catalytic hydrogenation, 3 was quantitatively converted into tetraisopropylmethane (4). X-ray structure analysis established S₄ symmetry for 3 and D_2d symmetry for 4, in excellent agreement with the B3LYP/6-31+G** computed structures.

Hard and soft centers: the donors O (hard), P and C (soft) are together in the multidentate, oxygen-substituted, anionic phosphanes I and II, which are particularly suitable for the synthesis of novel calcium organyls. With these mono- and dianionic ligands calcium organyl compounds, without cyclopentadiene ligands, could be prepared and structurally characterized: a sodium trialkyl calcate(II) and the first calcium organyl compound with a heterocubane structure. Ph′=p-tolyl.

A remarkable antenna effect observed in dendrimers with an anthracene core and dendrons of the Fréchet type (see picture) results in strongly increased fluorescence quantum yields relative to that of anthracene. The UV-induced [4π+4π] cycloaddition, in which the anthracene core reacts with a benzene ring of the dendrons, leads to novel photodimers.

A preference for inward over outward rotation is found for the thermal conrotatory ring-opening reaction of 1-cyclobutene 1, to produce 1,3-butadiene 2, when a silyl substituent is located at the 3-position. This preference exists in spite of the bulkiness of the substituent.

An advanced ABCD fragment (see picture) constructed on the way to the total synthesis of the potent antitumor agent (+)-spongistatin 2 has also been used in a formal total synthesis of (+)-spongistatin 1. In both cases the critical step was an acid-mediated epimerization in the presence of Ca²⁺ ions to stabilize the axial–equitorial CD spiroketal.

An advanced ABCD fragment (see picture) constructed on the way to the total synthesis of the potent antitumor agent (+)-spongistatin 2 has also been used in a formal total synthesis of (+)-spongistatin 1. In both cases the critical step was an acid-mediated epimerization in the presence of Ca²⁺ ions to stabilize the axial–equitorial CD spiroketal.

A closed spherical structure which can self-maintain or grow/reproduce depending upon the chemical parameter setting would be a simple chemical model of the homeostatic cell. One such model is presented here. It is based on oleic acid/oleate vesicles which host two competitive reactions which take place within the boundary of the bilayer, that is, one reaction which produces more vesicles and one which destroys them.

The intriguing mechanisms by which o-iodoxybenzoic acid (IBX) and Dess–Martin periodinane (DMP) transform anilides to heterocyclic systems (see scheme) have been extensively studied and elucidated, which has led to the design of further synthetic technologies.

A mechanistically inspired tandom Dess–Martin periodinane (DMP) induced oxidation sequence converts anilides into N-substituted p-quinones or o-azaquinones depending on the aromatic nucleus substitution. The application of this technology resulted in an expedient total synthesis of the potent anti-arthritic agent epoxyquinomycin B (see picture).

Catalyst and reaction medium in one: that is the dual role of supercritical water (scH₂O) in the disproportionation of benzaldehyde. In the near-critical region the reaction rates (k_p2) are significantly greater than those found in water and aqueous NaOH (see picture, values for scH₂O and water are at 25 MPa), also unequivocal chemical evidence for the participation of the OH⁻ ion, not the OH^. radical, is obtained.

An eight-membered cyclic dimer of the hydrosilane 1 a is produced through dehydrogenative Si−Si bond formation during the reaction of 1 a with a nickel complex to give 2. A possible intermediate in this dehydrocoupling reaction is the dinuclear silyl(μ-silylene)nickel(III) complex 3, which could be isolated from the reaction of the analogous hydrosilane 1 b with [Ni(dmpe)₂]. dmpe=1,2-bis(dimethylphosphanyl)ethane.

The functional groups and heterocyclic classes known to be compatible with a directed C−H activation with [Ru₃(CO)₁₂] has been expanded through development of a new substrate screening strategy. Following C−H activation, a library of products is MS-labeled and rapidly evaluated by positive ion electrospray ionization mass spectrometry (see scheme) to directly identify successful products and their yields.

An isolated reaction intermediate in the desulfurization of thiones promoted by phosphanes is provided by the ylide derivative 3, which is obtained by thiophilic addition of PCy₃ to 2. Complex 2 is formed from the disulfide-containing dimetallic complex 1 by scission of the S−S bond. [Mn]=Mn(CO)₄⁺, R=Ph.

Higher alkanes such as cyclohexane, cyclooctane, and adamantane undergo nitration with NO₂ in the presence of a catalytic amount of N-hydroxyphthalimide to form the corresponding nitroalkanes [Eq. (1)]. Furthermore, the nitration is conducted under air, and NO generated in the course of the reaction can be reoxidized by O₂ to NO₂, and thus reused in the nitration.

Electrodeposition of dendrimers containing redox-active tetrathiafulvalene units and coordinating crown ether moieties provides a novel strategy for producing modified electrodes that respond to the presence of a particular metal cation. Application of the third-generation dendrimer (see schematic diagram) to platinum gave an electrode whose first oxidation potential is a function of Ba²⁺ concentration in the range (1–8)×10⁻⁴ M.

A simple reduction of the Pd^II complex 1 affords the Pd^I dimer 2, featuring a μ₂ symmetrically bridging phosphole unit, and thus a novel coordination mode for a tertiary phosphane. Complex 2 appears to be very stable towards additional ligands such as CO and PPh₃, and the structural data are in accordance with calculations, which reveal that the Pd−Pd and Pd−P bonding is highly delocalized.

Catalytic asymmetric allylation (CAA) using tributyl-(2-ethylallyl)stannane as a methyl ethyl ketone equivalent plays a key role in this synthesis of rhizoxin D. A subsequent substrate-directed acetal aldol reaction, fragment assembly by a modified Julia procedure, and directed electron transfer reduction are used to complete the synthesis (see scheme).

A planar-chiral DMAP derivative, in conjunction with a readily available, novel acylating agent, effects the kinetic resolution of α-arylamines, a biologically important class of compounds, with a selectivity factor of up to 27 (see scheme). The catalyst used, PPY*, is the first effective nonenzymatic catalyst for the enantioselective acylation of amines. DMAP=4-dimethylaminopyridine.

Unprecedented geometries are displayed by two chromium–nickel–cyanide clusters that have recently been synthesized. [(Me₃tacn)₈Cr₈Ni₅(CN)₂₄]¹⁰⁺ exhibits a face-centered cubic structure with a Ni²⁺ ion missing from one face. This species reacts with [Ni(CN)₄]²⁻ to yield [(Me₃tacn)₁₀Cr₁₀Ni₉(CN)₄₂]⁶⁺ (shown in the picture), incorporating square-pyramidal and trigonal-bipyramidal [Ni(CN)₅]³⁻ and square-planar [Ni(CN)₄]²⁻ units in the largest metal–cyanide cluster reported to date. Me₃tacn=N,N′,N″-trimethyl-1,4,7-triazacyclononane.

Substitution of the iodide ions in the octahedral hexarhenium cluster [Re₆Se₈I₆]³⁻ by the diphosphane Ph₂P(CH₂)_nPPh₂ generates “bridge–chelate” complexes when n=6 (dpph) with general formula [Re₆Se₈I_6−2m(μ-dpph)_m]^2m−4 (m=1–3; the picture shows the trans isomer for m=2), whereas for n=5 only a monodentate binding mode of the diphosphane is found. Stepwise substitution by dpph strongly affects the redox processes, while the photophysical properties associated with the [Re₆Se₈]²⁺ core change only moderately.

A monotropic smectic A phase is exhibited by adducts of tris(β-diketonato)lanthanide(III) complexes with a non-mesomorphic salicylaldimine Schiff base as Lewis base. Only four terminal alkyl chains were necessary in the Schiff base to induce mesomorphism in [La(dbm)₃] (see formula). Hdbm = 1,3-diphenyl-1,3-propanedione (dibenzoylmethane).

One ring, two oxidations: The first doubly ring-oxidized metal phthalocyanine complex has been synthesized by galvanostatic electrocrystallization. Copper phthalocyanine was oxidized in the presence of perrhenate anions to form the new molecular compounds [Cu(pc)(ReO₄)] and [Cu(pc)(ReO₄)₂] (structure shown). Single-crystal EPR results show that the oxidation of [Cu(pc)(ReO₄)₂] is entirely ring-based.

Ruthenium vinylidenes: metathesis catalysis on the bench? Ruthenium vinylidene compounds 1, generated in situ from readily available, air-stable precursors, are used to catalyze ring-closing metathesis, ene–yne metathesis, cross-metathesis, and ring-opening metathesis polymerization. Bulky imidazolylidene ligands and terminal alkynes were found to be necessary components for achieving high catalytic activity.

Enantioenriched five-membered rings with a quaternary chiral center are prepared with remarkable efficiency by the ene-type carbocyclization of 1,6-enynes catalyzed by chiral palladium complexes (see scheme). Possible mechanisms including neutral (five-coordinate) and cationic (four-coordinate) intermediates have also been proposed.