Complexes containing the unsubstituted 1,3-butadiene-1,4-diyl ligand C₄H₄ are very rare. Such a complex, 1, has now been generated, surprisingly, by the unusual title reaction. In 1, the C₄H₄ ligand is linked unsymmetrically to three Cp^*ClHf moieties; the two remaining Cl atoms each bridge two Hf centers (Cp^* = η⁵-C₅Me₅).

The first isolable reduction products of white phosphorus, the title compounds, are formed upon reaction of P₄ with naphthalenelithium or -sodium/potassium in protic solvents. They contain the HP ion 1, which, according to its NMR data, displays an unusual electronic structure. Intramolecular exchange of the endo hydrogen atom does not occur.

The pentalene derivative 2 is only inductively stabilized. It was obtained by reaction of the dihydro derivative 1 with nickel peroxide. Comparison of the spectroscopic data with the results of MNDO calculations indicates that the Kekulé structure shown here dominates; that is, the bonds are fixed.

Methyl substituents—and the temperature—influence the Ni^II-catalyzed isomerization of 1,5-cyclooctadienes. For example, reaction of isoprene in refluxing hexane leads, via 1, to the bicyclic compound 2 and reaction of isoprene and trans-piperylene leads, via 3, to the highly strained tricyclic cyclopropane derivative 4. The structures of the carbon frameworks were established by 2D INADEQUATE NMR experiments.

Fused-ring arenes such as naphthalene can be subjected to considerable deformation. This is exemplified by the structures of the two title compounds. They also provide further support for the suggested stability of such molecules as the three-dimensional, sphere-shaped cluster C₆₀ (“Buckminsterfullerene” or “Footballene”), which consists of 60 sp²-hybridized carbon atoms. The phane-diene is shown on the right.

A largely solvent-separated ion pair 3 is the presumed intermediate in the hydroxylation of cyclohexenes with SO. Radical anions like 1 and 2 are formed in a nearly diffusion-controlled step. They are subsequently hydrolyzed via 3. The axial/equatorial selectivity of the reaction of H₂ O with 3 is much greater than that observed in the reaction of OH^⊙ with 4-tert-butylcyclohexene (90:10 vs. 58:42).

The characterization of paramagnetic compounds in water by ENDOR spectroscopy was achieved by the use of special capillary tubes and optimal concentrations. This extension of the scope of application of this method is of great value for the study of biological redox reactions. The method was exemplified by determining the spectrum of the radical cation 2, R = n-dodecyl. This compound was obtained by reduction of the viologen 1.

The first two dications having a [HBP₃]^{2 ⊕} framework (1 and 2)—the boron atom is surrounded by three phosphonium centers and a hydrogen atom—were isolated as dibromides and characterized by X-ray structure analysis. The stability of the two salts toward air and moisture is remarkable. The boron-bonded H atom is exchanged for a D atom in alkaline D₂O.

Reaction of the long-known cyclotetrasilzane derivative 1 was accomplished for the first time without ring-opening, namely by treatment with nBuLi to afford the dimer [2]₂, in which two eight-membered rings are joined through an (LiN)₂ four-membered ring. Depending on the molar ratios used, reaction of 2 with PhSiF₃ results in either disubstitution or bridging to give 3.

Azirineimine, formally an HCN dimer, was obtained for the first time as derivative 1. Compound 1 is formed upon reaction of 1,2-O-isopropylidene-3,5,6-tri-O-p-toluenesulfonyl-α-D-glucose with KCN in nitromethane/water under phase-transfer conditions. Theoretical studies have shown that azirineimine may have played a role in the prebiotic formation of organic compounds.

Compound 1 has an azagallapropellane structure in which the GaR₃ unit is stabilized intramolecularly by the N atom. Ga has a trigonal-pyramidal environment. Compound 1 is formed from GaCl₃ and the Grignard derivative of tris(3,3′,3″-chloropropyl)amine. Despite the coordinatively unsaturated pyramidal base, 1 is remarkably stable, for example toward oxygen.

A [3]radialene having strong electron-donor properties, the title compound 1, was formed upon reaction of lithium thioxanthenide with hexachlorocyclopropane after addition of BuLi. Cyclic voltammetry in CH₂Cl₂ gave two pairs of reversible waves corresponding to the formation of 1^⊙⊕ and 1^2⊕. A thermally accessible triplet state, only 0.07 eV higher in energy than the singlet state, was established for dark blue 1^2⊕·2CF₃CO by ESR spectroscopy. Thus, 1 might serve as a donor component for the preparation of organic ferromagnets.

NMR data show that the title compound 2 has a highly symmetrical structure—a propeller-like arrangement having D₃ symmetry is plausible. Compound 2 was prepared by cyclotrimerization of the ate complex 1. An explanation for the easy, reversible, two-step reduction of 2 to its dianion may be provided by the importance of the dipolar resonance structure 3 in describing the actual structure of the dianion.

The answer is probably no, even though it violates common expectations. Calculations on 1–3, taking into consideration electron correlation, gave 1 as the highest-energy species at all levels of approximation. This reflects once again the fact that—in contrast to the carbon analogues—Si₃ rings are more highly strained than Si₄ rings.

Generation of the thermally unstable 1,2-dilithioethane 1, which had eluded earlier synthetic attempts, has now been carried out under special conditions. Condensation of lithium vapor on a glass formed from ethylene and dimethyl ether at — 196°C yielded highly active lithium, which, upon melting of the glass, reacted with ethylene to afford 1. Compound 1 was identified by carboxylation and methylation to give the ester 2 and by stannylation to give the bis(stannane) 3.

“Organolithium-like” behavior of phenylmagnesium compounds is possible to achieve using the activating influence of the crown ether derivative 1. Halogen-metal exchange and metalation were previously considered to be reactions characteristic of organolithium (but not organomagnesium) compounds. The new reactions are also of preparative interest (X = Ph, Br; Y = H, Br).

The β-mannoside bond in the core region of N-glycoproteins is difficult to form. The epimerization at C-2 of β-glucosides, which is normally difficult to achieve, has now been accomplished by intramolecular nucleophilic attack of a carbamate substituent in the sense of neighboring-group assistance. It was possible in this way to prepare directly isomerically pure (protected) β-mannosides like 1 from menthol and cholesterol as well as β-mannosidic disaccharides.

The same educt, homologous reagents, products having analogous empirical formulas—yet totally different structures! Whereas Ge¹¹ is incorporated into the cyclodisilazane 1 to form the bis(germanediyl) 2 containing divalent Ge, 1 reacts with Sn¹¹ to form the stannate 3 containing trivalent Sn. These results are ascribed to ring-strain effects (R = tBu).

The synthetic carba(dethia) analogues of coenzyme A contain a —CO—CH₂—instead of a —CO—S— group and are therefore hydrolytically stable. The isobutyrylcarba(dethia) coenzyme A 1, whose synthesis is reported here, is isomerized to the n-butyryl derivative 2 by a cell extract from Streptomyces cinnamonensis (monitored by ¹H NMR). This new, coenzyme B₁₂-dependent structural rearrangement is similar in many ways to the long-known methylmalonyl-CoA mutase reaction.

Monomeric metalated sulfones like 1 are a rarity. In 1, K^⊕ is bonded only to the O atoms of the sulfonyl group. Accordingly, the negative charge is stabilized largely by polarization and negative anionic hyperconjugation. Comparison of the effect of metalation on the ¹J(¹³C, ²⁹Si) values of several carbanions stabilized by Si (and S) showed that these coupling constants are good probes for the structure of carbanions in solution.

Inorganic double helices having 2 and 2.5 turns are formed by the tetra- and penta(bipyridine) ligands 1 and 2, respectively, upon addition of Cu¹ salts. These polynuclear complexes, in which the copper ions are aligned like a string of pearls, are estimated to be about 22 and 27 nm long, respectively.

The biologically highly active calichemicin γ contains the benzoate 1 — glycosylated on the OH group and linked through the ester group (S instead of O), via sugar moieties, to other unusual organic fragments. Compound 1 has now been synthesized in five steps from 3,4,5-trimethoxytoluene and has proven to be very interesting. It undergoes spontaneous enantiomer resolution upon crystallization and exhibits second harmonic generation activity.

Direct comparison of the cyclopentadienyl ligand with its open-chain counterpart has been accomplished using complex 1, which contains both ligands. The Ti-C bonds to the acyclic ligand are 0.106 Å shorter than those to the cyclic ligand. Although this finding indicates that the bonds to the pentadienyl ligand are stronger, reaction of 1 with acetonitrile occurs nonetheless at this ligand. The aromatic character of C₅H offers a possible explanation for this apparent contradiction. The aromaticity results in resistance to chemical change; that is, both formation of stronger bonds and coupling with electrophiles are disfavored.

Triblattanes, such as the previously known 1—(+)-1 is shown here—are very promising, novel cage molecules. For example, 1 can be transformed efficiently into [2.2.2]-triblattatriene (+)-/(-)-2, a C₁₄H₁₄ pentacyclic compound, by means of a threefold ring expansion. Like its similarly obtained tribenzo derivative, 2 has D₃ symmetry. The chemical versatility of 2 and its precursors is exemplified by the generation of the hexaketone 3, which was trapped as its triquinoxaline derivative.