Site-directed and efficient labeling of amino acids in biological receptors is possible with ligand analogues that form reactive intermediates on irradiation. This approach was used to label the binding sites of many receptors, for example by photoinduced coupling with (radioactive) nitrenes, carbocations, carbenes, and excited ketones [Eq. (a)]. The labeled amino acids are identified by proteolysis of the complex, purification, and sequencing. This method is well-suited for the study of ligand—receptor interactions and provides useful information for site-directed mutagenesis. □ = ligand, * = radioactive label, AA1, AA2, AA3 = amino acids.

Efficient trapping of the liberated fluoride ions is the key to the synthesis of the hexakis(onio)-substituted benzene derivative 1 in 92% yield from hexafluorobenzene and dimethylaminopyridine. In the solid state one of the triflate counterions of 1 is located above and one below the central benzene ring to give a triple-decker-type structure.

An unusual, additional side-on coordination of an iridium center and a rhodium complex fragment with 16 valence electrons is realized in the new compounds 1. Compounds 1a, E = P, M = Ir, and 1b, E = As, M = Rh, were prepared from the sandwich complexes [Cp^*Fe(η⁵-E₅)]. The isomers of 1a and 1b with terminal η¹ coordination of the metal complex fragment have been obtained as well.

En route to highly colored chromophores, quaterrylenebis(dicarboximides) 1 were prepared, which can function both as pigments and soluble dyes. The polycycles absorb at very long wavelengths and are remarkably stable. R = H, R′ = C₁₂H₂₅; R = OC₆H₄-p-tBu, R′ = o,o′-iPr₂C₆H₃.

Formally only 12 valence electrons are assigned to the Rh^I atom in the cyclo-M₃ clusters in the title. This electron deficiency is compensated by π-electron delocalization in the M¹-Rh-M² three-membered ring, and the unusual threefold coordination of the d⁸-Rh^I atom (see picture on the right) is thus stabilized. The cluster can be synthesized in good yields from [Rh(CO)(PPh₃)]Cl and PPh₄[M¹M²{μ-P(C₆H₁₁)₂} CO₈].

An indirect strategy was needed for the first synthesis of a labile dNDP-3-keto sugar, the title compound 2. D-Glucose is converted into methylene phosphate 1, which after ozonolysis and linkage of thymidine monophosphate, provides 2. According to present knowledge the target compound is an important intermediate in the biosynthesis of dideoxy, trideoxy, aminodeoxy, and branched sugars.

The insertion of titanocene, prepared from the corresponding dicarbonyl complex, into SS bonds of S₇NH and S₇NMe affords the complexes 1 and 2, respectively, which are suitable as precursors for large SN rings. The treatment of 2 with SCl₂ and S₂Cl₂ yields the imides S₈NMe and S₉NMe, respectively.

Complete B-methylation is possible for 1,12-dicarba-closo-dodecaborane(12) derivatives that are substituted on one or both carbon atoms. Electrophilic substitution under harsh conditions affords rigid “hydrocarbon balls” in high yields. An example of these carboranes, the title compound (shown as a space-filling model on the right), has twelve methyl groups arranged in an icosahedral manner and supported on a carborane skeleton.

A strongly twisted distannene (shown on the right) is found in crystals of bis(hypersilyl)tin 1. In its violetbrown solutions 1 is mainly monomeric, as is the blue bis(hypersilyl)lead 2.

An electron-rich phosphanegold complex is used in the first catalyzed diboration of alkenes. The reaction of diborane 1 with alkene 2 in the presence of [AuCl(PEt₃)] and ethane-1,2-diylbis(dicyclohexylphosphane) yields exclusively the 1,2-bis(boronate) ester 3.

Both natural oligoribonucleotides and oligodeoxynucleotides are hybridized sequence-selectively by hexitol nucleic acids (HNA) 1, which are composed of 1,5-anhydrohexitol nucleoside analogues linked by phosphate groups. Owing to the strongly increased duplex stability, these constructs should be pursued for potential applications as antisense agents.

Despite three neighboring electron-deficient centers, dicarborylcarbenes are not too high in energy to be accessible thermally. This was shown by the low activation enthalpies (≈22–23 kcal mol⁻¹) of double 1,2-rearrangements of borylmethyleneboranes, in which alkyl groups migrate from carbon to boron and aryl groups from boron to carbon. Ab initio calculations reveal that tetramethyldiborylcarbene 2 is only 23.1 kcal mol⁻¹ higher in energy than tetramethylborylmethyleneborane 1.

Fullerenes with enlarged openings such as diazafulleroid 1 are obtained by twofold addition of azides to C₆₀. Even after cleavage of the two 5–6 bonds and introduction of the imino bridges, the π-electron system of C₆₀ remains intact. Compound 1 contains three seven-membered rings and one eleven-membered ring, and may hold the key to the synthesis of endohedral fullerenes under mild conditions.

An efficient and simple approach is described here for the synthesis of enediyne 1, a model compound for the antibacterial and anticancer agent dynamicin A. Compound 1 undergoes the cycloaromatization reaction characteristic of such enediyne systems and can conceivably be attached to various “drug delivery systems” through the two ester groups.

A facile Pd-catalyzed method for the preparation of a wide variety of aryl amines from aryl bromides and amines has been developed [Eq. (a)]. Noteworthy features of this method include the experimental simplicity, the tin/boron-free conditions, and the broad spectrum of potential substrates.

A trimeric palladium complex results from the reaction of Pd(OAc)₂ and the sulfoxide 1. A section of the structure of this complex, which is obtained enantiomerically pure in the (R,R) form and contains two dative and two covalent bonds to palladium, is shown at the bottom on the right.

An amazingly simple access by dissolving barium metal in tBuOH, addition of nBuLi, and crystallization from THF/hexane leads to the polyion aggregate 1. The novel polyhedral Ba₆Li₃O₂ core has a charge of 11⁺ and is surrounded by an ellipsoidal C₅₆H₁₂₃ hydrocarbon skin. Density functional calculations for a 33-center/460-electron model revealed that it is indeed a polyion aggregate, and that weak interactions exist between the two oxygen centers in the polyhedron. In the second communication the hydrocarbon ellipsoid of the polyion aggregate consists of 24 phenyl groups, and the interactions between them are analyzed.

An amazingly simple access by dissolving barium metal in tBuOH, addition of nBuLi, and crystallization from THF/hexane leads to the polyion aggregate 1. The novel polyhedral Ba₆Li₃O₂ core has a charge of 11⁺ and is surrounded by an ellipsoidal C₅₆H₁₂₃ hydrocarbon skin. Density functional calculations for a 33-center/460-electron model revealed that it is indeed a polyion aggregate, and that weak interactions exist between the two oxygen centers in the polyhedron. In the second communication the hydrocarbon ellipsoid of the polyion aggregate consists of 24 phenyl groups, and the interactions between them are analyzed.

Deprotonation of the conjugate acid 2 led to the first gallatabenzene 1. The acidity of 2 and the low-field shift of the NMR signals of the ring protons of 1 relative to the corresponding properties of cyclohexadienide suggest that 1 has aromatic character. The heterocycle of 1 can function as a ligand and was coordinated to a Mn(CO)₃ fragment.

New tetraamidato ligands with appended urea moieties have the requisite electrochemical and structural properties to stabilize the dioxoosmium(IV) cation through multiple interactions. In the corresponding 1:1 complexes four strong bonds between metal and nitrogen donor and an additional hydrogen bond between each oxo ligand and a C(O)NHR moiety are responsible for the stability. The primary coordination sphere of an osmium complex of this type is shown on the right.

Attraction of the charges on the participant atoms causes the polar covalent NS and NP single bonds in the cation of the phosphorane iminato complex [S(NPMe₃)₄]Cl₂ (shown on the right) to approach the lengths of double bonds. This is in agreement with the results of ab initio calculations. The complex was obtained from S₂Cl₂ and the silylated phosphorane imine Me₃SiNPMe₃ in acetonitrile.

A large, soft Cs⁺ ion nests in the cavity of [1.1.1]-paracyclophane (1), giving rise to a stable [1 · Cs]⁺ complex (space-filling model on the right), which can be detected in the gas phase by mass spectrometry. Crucial to the formation of this complex is the interaction of the Cs⁺ ion with all four arene rings. The somewhat smaller Rb⁺ ion also forms a stable complex with 1, but Li⁺, Na⁺, and K⁺ are too small to interact effectively with the cavity of 1.

Three steps suffice for constructing the pyrroloindolino framework of the pharmacophoric moiety 2 of the highly potent anticancer agent CC-1065. The easily accessible bis(allylamino)bromobenzene 1 was transformed by successive cyclizations mediated by [Cp₂Zr(Me)Cl] and by a Pd° complex.