The lectures delivered in Stockholm by last year's receivers of the Nobel prize for Physics are of great interest for chemists since both electron- and scanning-tunneling microscopy are used in surface studies. The three laureates give colorful historical accounts of the development of their techniques without neglecting interesting human aspects—“some joyful events and many disappointments” (Ruska). One of the first highlights of scanning tunneling microscopy was the elucidation of the 7 × 7 reconstruction of the Si(111) surface, see picture.

The lectures delivered in Stockholm by last year's receivers of the Nobel prize for Physics are of great interest for chemists since both electron- and scanning-tunneling microscopy are used in surface studies. The three laureates give colorful historical accounts of the development of their techniques without neglecting interesting human aspects—“some joyful events and many disappointments” (Ruska). One of the first highlights of scanning tunneling microscopy was the elucidation of the 7 × 7 reconstruction of the Si(111) surface, see picture.

The clinical success of cisplatin 1 in the chemotherapy of tumors encouraged a search for analogues with lower toxicity, better therapeutic index, and higher activity. Thus far, however, only very few of the “traditional” analogues have proven promising in clinical tests. The use of carrier, molecules or chemotherapeutics as ligands and/or of complexes with several Pt atoms could possibly lead to better results.

Couplings between ¹³C nuclei afford information directly on the carbon-carbon connectivities in the carbon skeleton, but, however, they were hitherto extremely difficult to observe because of the low natural abundance of ¹³C. It is now possible to use a special NMR pulse sequence to make such couplings more readily visible. For example, the constitution of the tricyclic ketone 1 (CO groups not shown) could be determined by two-dimensional INADEQUATE-¹³C-NMR spectroscopy.

Other than the formula would suggest, 1^2⊕ has a globular “tertiary structure” both in solution and in the solid state; this was revealed by NMR studies and an X-ray structure analysis, π-π interactions between aromatic subunits probably contribute to the stability of the tertiary structure of the Cu₂-[3]-catenate (stacking arrangement).

Striking antibiotic and cytotoxic properties are exhibited by the products 3 and derivatives thereof. Compounds 3 are obtained in good yields from the chiral diene streptazolin 1 (R³  H) and naphthoquinones 2. The low endo-/exo-selectivity and diastereofacial selectivity of the cycloaddition are, by way of exception, an advantage; they make a number of isomers accessible for the screening of natural products. (R¹, R²  H, OH, OAc; R³  H, Ac, SiMe₂tBu.)

The flash vacuum pyrolysis of 1-chloro-1-boraindane 1 leads with dehydrogenation to the 1-benzoborole 2. The highly reactive, antiaromatic system dimerizes regiospecifically even at low temperatures to the diboradibenzotetrahydroazulene 3. Trapping reactions with 2-butyne. DCl and CH₃OD furnished products which likewise suggest intermediary occurrence of 2.

Despite their importance as potential intermediates, carbenevanadium complexes are still a rarity. Reaction of (butadiene)zirconocene or (butadiene)hafnocene with [CpV(CO)₄] affords 1, which for M  Zr is in equilibrium with the reaction partners in solution, whereas for M  Hf it is in equilibrium with 2.

Selective excitation of the N  N π electrons of 1 led to the first cyclopropapyridine 3. Compound 3, which is presumably formed by ring closure from the diradical intermediate 2, is acid-labile, but seemingly stable in the crystalline state under argon (R  NCOPh).

The first stable silanediyl complex 1 is monomeric both in solution and in the crystalline state. 1 has a polar SiFe bond and is stabilized by adduct formation with hexamethylphosphoric triamide (HMPT). As expected, the silanediyl ligand occupies an apical position of the trigonal-bipyramidally coordinated iron atom.

[4 + 2]-Cycloadducts of two different 1,3-dienes can be the result of a Diels-Alder reaction or a Diels-Alder reaction and subsequent Cope rearrangement. This duality is manifested in the mobile equilibria between 1-H^⊕, 2, 3, and 4-H^⊕. The rearrangement 3 + H^⊕ → 4-H^⊕, a novel diaza-Cope rearrangement, is more rapid than the cycloreversion to 1-H^⊕ and 2.

The acid-catalyzed [4 + 2] cycloaddition of the cyclic azines 1 with the 1,3-dienes 2 leads to a mixture of the azo compounds 3 and the hydrazones 4.3 and 4 are interconverted by acid-catalyzed [3.3] rearrangement. The structural dependence of this novel Cope rearrangement corresponds to the energy differences of 3 and 4, which were estimated by force field calculations. X

A longer GeGe bond than in polygermanes is found in the “bisgermanediyl” 1, which is thus in no way comparable with digermenes R₂GeGeR₂. The very stable Ge₁ compound 1 with lone pairs at the Ge centers is formed upon reaction of GeCl₂ with the phosphinomethanide [(Me₃Si)(Me₂P)₂C]^⊖ in excess.

The title compound, a Ge^I-Ge^I-Ge^II-Ge^I-Ge^I polygermane is completely dissociated in solution at room temperature; in the solid state there is an almost linear GeCl₂ moiety surrounded equatorially by two-ligands 1. The structure of the resulting angular Ge₅ chain with the two Cl atoms is shown on the right.

[μ-{(Me₃Si)C(PMe₂)₂}]₂Ge₂ 1

Colloid-chemically synthesized gigantic gold and silver clusters and microparticles have been investigated by high-resolution electron microscopy. In the case of the gold samples decahedral and icosahedral, multitwinned and triangular flattened particles were characterized. In the silver samples there were extremely small particles (<40 Å, see right-hand side of picture) whose structure is interpreted in terms of a pentagonal packing of the atoms. The inset shows a structural model (left, top) and a computer-simulated image (left, bottom).

Structural studies of the photosynthetic reaction center (RC) have revealed that both donor-acceptor distances and inter-macrocycle orientations play a crucial role in mediating the photosynthetic charge separation process. Numerous photosynthetic model systems have already been synthesized and studied in an effort to understand the first of these factors, while intermacrocycle effects have not been thoroughly addressed in model systems. Models with various fixed angles between the porphyrin units have now been synthesized for the first time: the linear 1 and a “gable”-type analogue. Solutions of both compounds in toluene showed no detectable fluorescence when irradiated at 418 nm.

The two title compounds are a neutral complex and a homonuclear ion pair, respectively. The carmine-red Co₇-complex consists of an octahedrally coordinated Co²⁺ central ion surrounded by four pyridine ligands and two [Co₃(CO)₁₀] clusters. The cation of the emerald-green Co₃ complex has the structure 1.

A distorted tetrahedral environment, a bond length typical for terminal AlC bonds, and unusually small AlN distances characterize the cation 1, which is formed on addition of AlCl₃ to the corresponding chloride. The AlN distances show that Lewis acid-base interactions are required for the stabilization of a dialkylaluminum ion.

The chiral non-racemic glycine cation equivalent 1 enabled the synthesis of the previously unknown methyl (R)-α-arylglycinate 3. The Friedel-Crafts adducts 2 could be hydrolyzed without epimerization or racemization with 2 equivalents of 0.1 N HCl. α-Arylglycines are of particular interest as pharmacophoric building blocks of drugs. (R¹–R⁴  H, OEt, OMe.)

A type of coordination important for cluster-surface analogy could be realized on two counts at one and the same time in the complex 1: the two μ₄-CO ligands in 1 are so arranged that the C atoms each bridge a Ru₂Mo triangle and the O atoms are additionally bound to a further Ru atom; the CO distance is large (1.25(1) Å).

To a CH₂ Ligand! is the answer to the question posed in the title—an indirect confirmation of the concept already proposed by Fischer and Tropsch regarding the growth step of the synthesis bearing their names. The reaction was found to take place in the Os complex 1, from which an H^⊖ ion can be split off. The ethene complex 3 is formed from the presumed intermediate 2 by CH₃-migration and β-H shift.

The bonding situation in CsHg, which contains isolated, square-planar Hg₄ clusters, lies between that of the two extremes (Cs^⊕)₄(Hg₄)^4⊖ and (Cs^⊕Hg₄)⁰4e^⊖. The temperature dependence of the specific electrical resistance of this gold-bronze, extremely air-sensitive compound proves it to be a metal, so that the formulation with free electrons may be regarded as the more appropriate one. The picture on the right-shows a section of the crystal structure of CsHg (distances in ppm).

The title compound 2 could be the most strained monocyclic allene. It is generated from 1 by reaction with n-butyllithium and can be trapped with a series of alkenes. Thus, with styrene the diastereomeric [2 + 2] adducts 3 are formed. 2 reacts with 1,3-dienes to give [2 + 2]- and [2 + 4]-adducts, and, in the absence of reactive partners, 3-n-butyl-2,4-pentadien-1-ol is formed from 2 upon addition of n-BuLi.

Second sphere coordination of two receptor molecules to a metal complex has been observed for the macropolycycle 1. [Pt(NH₃)₄][PF₆]₂ forms discrete adducts with two molecules of 1; H-bridges between carbonylO and etherO atoms on the one hand and NH₃ on the other are crucial. Cisplatin does not form any adducts with 1.

A T-arrangement of two benzene rings contributes—aside from H-bridges—to the stabilization of a 2:1 adduct of the molecular receptor 2 with [Pt(NH₃)₄]^2⊕ in the solid state (X-ray structure analysis); in [D₆]acetone only a 1:1 adduct is present (¹H-NMR). With the same cation, 1 forms only 1:1 adducts in solution and in the solid state. Thus, small changes in the ligands can drastically alter its bonding properties (1, R  H; 2, R  Me).

A good model for the structure or allyl-Grignard compounds in solution is the crystal structure of the title compound. Dimers are present—half of such a dimer is shown on the right—which are coupled via MgClMgCl four-membered rings. The C9-Mg distance is 217.9(3) pm and lies in the range of other CMg distances in alkyl-Grignard compounds. The CC distances in the allyl group are different: C9-C10 = 144.2(4) and C10-C11 = 133.5(4) pm.

The isomers 2 count among the few unequivocally characterized Zr^III-alkyl compounds. They were prepared from 1 and MeLi exploiting the fulvalene bracketing effect. Further functionalization of 1 without fragmentation has also been achieved.

The spontaneous transformation of soluble polypeptide helices into insoluble sheet structures upon combining the two enantiomeric helices (shown schematically in the picture on the right) implies that metastable superstructures have longevity in solution when they are made up of chiral subunits. On combining clear solutions of the title compounds, which are stable for weeks, the racemate immediately precipitates in almost quantitative yield. Apparently the extremely large surface areas (energies) due to the curvature of the helices impairs crystallization, whereas crystal planes without curvature can be formed in the racemate.

A very rapid intramolecular two-electron transfer between Ru⁰ and Ru^II or a species with two Ru^I centers is the explanation given for the unusual properties of the cation of 1. ¹H- and ¹³C-NMR spectra are highly symmetric, and further reduction to the Ru neutral complex first takes place at −1.177 ± 0.010 V (vs. SCE). The phenanthrene analogue of 1—one double bond more—behaves completely differently; it obviously contains an Ru^II center and an Ru⁰ center.

In a preparatively facile reaction with Re₂O₇/Al₂O₃ as catalyst and using the dilution principle in a Soxhlet-like recycling apparatus, the metathesis of cycloolefins, which normally leads to unsaturated polymers, can be steered to macrocycles. Cycloheptene, for example, is smoothly converted into 1,8-cyclotetradecadiene (selectivity 80%! yield 68%).