The smallest C_n clusters produced to date by [2 + 2] cycloreversion (cyclo-C₁₂ and cyclo-C₁₆) as well as cyclo-C₂₀ can be synthesized from propellane-annelated dehydroannulenes (1–3). Spectroscopic data indicate that the dehydroannulenes have either a planar (2) or a puckered (3) conformation.

A convenient route to the stanna[n]ferrocenophanes 1 and 2 is presented. The series of homologous hetero[2]ferrocenophanes of the type [Fe(C₅H₄EMe₂)₂] (E = C, Si, Sn) is thus supplemented by 1. A comparison of the molecular structures (for E = C, Si, Sn) reveals that as the EE bond length increases, the strain in the [2]ferrocenophane molecule decreases.

What is the smallest tilt angle necessary for an [n]metallocenophane to undergo ring-opening polymerization (ROP)? In previous work [n]metallocenophanes with tilt angles of up to 13° were found to be resistant to thermally induced ROP. The stanna[1]ferrocenophane 1, the first [n]metallocenophane containing a heavy main group element in the bridge, has a tilt angle of only 14° but still polymerizes to yield novel high molecular weight poly(ferrocenylstannane)s 2.

Same composition but different structures characterize the manganese complexes 1 and 2 of the formula [Mn₂(bpym)(N₃)₄], which are obtained by the reaction of manganese(II) nitrate with 2,2′-bipyrimidine (bpym) and sodium azide in aqueous solution. Compound 1 has a honeycomb layered structure (shown on the right) and exhibits overall ferromagnetic interactions; 2 has a three-dimensional polymeric structure and shows overall antiferromagnetic interactions.

Glycosyl transferases provide rapid access to defined oligovalent sialyl Lewis^x structures (SLe^x) attached to a peptide backbone such as compound 1. MALDI-TOF mass spectrometry proved to be an elegant, reliable method for monitoring the individual glycosylation steps.

Dynamic systems consisting of heterocyclic substrates like 1 and a model receptor can be resolved by EPR and ENDOR spectroscopy because of the difference in time resolution of these techniques. Intermolecular interactions in these lock-and-key complexation equilibria influence the intramolecular flexibilities. R = CH₃.

Self-assembly of new tetranuclear (1) and octanuclear (2) manganese carboxylate clusters is controlled by the bis(bipyridine) ligands L1 and L2, respectively, which are shown on the right. The cation 1 consists of two Mn₂O complex fragments, each of which contains one Mn^II and one Mn^III center; 2 contains two butterfly-like Mn₄O₂ cores linked by bis(bipyridine) bridges. Counterion: ClO.

A link has been forged between porphyrins and annulenes by carbaporphyrins 1 (R = H and CH₃), in which one nitrogen atom of the porphyrin framework is replaced by a carbon atom. These novel compounds are 18π arenes like porphyrins and have similar spectroscopic properties.

A transition metal catalyst can trigger the cycloaromatization of an enediyne. A coordinatively unsaturated rhodium complex catalyzes the cyclization of the acyclic enediyne 1 to produce 3. The cyclization, which is similar to the Myers reaction, proceeds via a vinylidene–rhodium intermediate and the 1,4-organorhodium diradical 2. Rh = [RhCl(iPr₃P)₂].

Two distorted Fe₆O₆ hexagonal prisms with a common rectangular face form the core (shown on the right) of the decanuclear iron complex 1. Magnetic studies indicate a high-spin ground state of around S = 11 or 12. Hchp = 6-chloro-2-pyridone.

From an arene-rich liquid clathrate medium the title compound can be isolated in crystalline form. It is the first example of a compound in which an ionophore is stabilized by NH – π interaction. The crystal contains a linear supramolecular complex comprising five components (see picture) in which the cryptate molecules are elongated along their long axes.

The handedness of helical polybipyridine metal complexes can be induced by a template, as shown schematically below. Introduction of one linking stereoelement at one end of the strands sets the trend of the complexation, and the stereochemical information is transmitted over nanometer distances.

A new bonding mode is present in the title compound, in which a metalloporphyrin serves as a π ligand. The results of an X-ray crystal structure analysis (shown on the right) and spectroscopic studies clearly show that the metalloporphyrin is strongly affected by the complexation.

A phthalate group serves as the trigger for controlling the stability of the enediyne precursor 1. β-Elimination of this trigger generates the corresponding enediyne and the DNA-cleaving biradical. The highly strained nine-membered ring in 1, an analogue of the kedarcidin chromophore, was constructed by a transannular [2,3] Wittig rearrangement. Incubation of supercoiled DNA with 1 (1 mM) leads to double strand cleavage without the addition of a reducing agent, which is required for other DNA cleaving systems.

The simple reaction of a tris-bpy ligand strand with FeCl₂ leads to the self-assembly of the unique cation 1, which consists of a torus formed by five ligands wrapped around five Fe^II ions in a double-helical fashion and closed around a central chloride ion. This structure, a fivefold circular helicate, is a helicate analogue of circular DNA.

The titanium-mediated coupling of Ni^II and Zn^II pyrophaeophorbides results in formation of planar ethenefused bisphaeophorbides 1, M = Ni, Zn. Absorption spectroscopy indicates that the two chlorin units are highly conjugated, and the X-ray crystal structure shows the two phaeophorbide rings to be almost coplanar.

Tales of the Unexpected. The thermal reaction of aryl-substituted enyne allenes 1 does not proceed by the expected Myers-Saito cycloaromatization. Instead a novel cyclization via intermediate benzofulvene biradicals 2 takes place.

A new type of photopolymerization (depicted on the right) relies on well-defined, early transition metal complexes. Schrock-type catalysts are photochemically generated from di- or trialkyl tungsten complexes. The photoactivity and latency of the new catalysts are demonstrated by photo-differential scanning calorimetric and viscosimetric measurements.

Diastereoselectivities at previously unattained levels. Aziridines 2 can be prepared from precursors 1 via the Ti or Al enolates in > 99% de. Further advantages of this approach are the easy access to 1 by AlMe₂Cl-catalyzed 1,4-addition of O-benzylhydroxylamine to α,β-unsaturated chiral imides, and the straightforward recovery of the chiral auxiliary by treatment with lithium benzyloxide. R = Me, Et, nPr; M = TiCl₄, AlMe₂Cl.

Functionalization of a phosphane ligand facilitates intercalation of the free ligand and its tungsten pentacarbonyl complex (example shown bottom right) in α-zirconium phosphate (section of structure shown bottom left). Syntheses of intercalated products with the stoichiometry [Zr(HPO₄)₂(Q)_x·yH₂O] (Q = Ph₂PCH₂CH₂NMe₂, x = 0.46, y = 1.1; Q = (OC)₅W(Ph₂PCH₂CH₂NMe₂), x = 0.51, y = 1.5) are reported.

Smoothly and in good yield, the reaction of 1,2-disilylbenzene 1 and the palladium complex 2 affords the silylpalladium(IV) complex 3. Compounds like this might be intermediates in catalytic transformations of silanes.

Trigonal-bipyramidal and octahedral coordination is found in transition metal complexes 1 and 2 (M = Co, Ni, Cu, Zn; X = Cl, NO₃, NCS (or SCN)) with dendrimeric ethyleneimine ligands of the first (¹ = H; R² = CH₂-3,4-C₆H₃[O(CH₂)₉CH₃]₂) and second generation (R¹ = R² = CH₂CH₂NHCO-3,4-C₆H₃[O(CH₂)₉CH₃]₂). These complexes form a novel class of metallomesogens. With a second generation dendrimer as the ligand or with Zn^II as the central atom, a hexagonal-columnar phase is formed. Otherwise, lamellar mesophases are obtained.

In the absence of strong π acceptors or soft Lewis bases (PR₃) acting as competing ligands, the aminoalkyl-functionalized Cp ligand unfolds its full potential in coordination chemistry. This is exemplified by the synthesis of the unusual silanediyl(silyl) complex 1.

Only the convex face of the chiral, cyclic nitrone 1 is accessible to dipolarophiles 2 in [3 + 2] cycloadditions. Since in addition Z² dictates the orientation of the dipolarophiles by directing the smallest substituent (H) of 2 into the most demanding space, the cycloadducts 3 are obtained with almost perfect stereocontrol.