One mechanism is sufficient to describe numerous organic and organometallic reactions if the nucleophiles and electrophiles are also regarded as electron donors and electron acceptors, respectively. The resulting free energy relationship for electron transfer (FERET) makes it possible, for example, to describe such different reactions of TCNE as the cycloaddition to anthracene () and the insertion into M-X bonds (⊙) by a common linear free energy relationship.

Low- and high-molecular-weight clusters having unusual structures and valence-electron concentrations are accessible by reactions between halide complexes and silylated chalcogen and pnictogen compounds. One example of the many clusters described is 1, in which sulfur displays three types of coordination. Such compounds provide information of importance to both solid-state and complex chemistry.

“By no means is it of merit to make an accidental discovery. Much more important is the recognition of possible consequences that might result from serendipity.” Trioxo(η⁵-pentamethylcyclopentadienyl)rhenium(VII) 1, prepared by chance several years ago, has proved to be a versatile compound, the methyl analogue of which, 2, has also borne fruit. These compounds have enhanced our understanding of olefin metathesis, the oxidative coupling of alkynes, and the oxidation of olefins. Perhaps it will soon be possible to synthesize the WO₃ and OsO₃ relatives, 3 and 4, respectively.

Laser chemistry can be employed in thin film deposition as well as in (structuring) ablation and etching. In general, reactions at surfaces can be initiated or assisted with lasers, as shown by the diverse examples in this article. One such possibility is the surface deposition of highly disperse powders, for example, silicon carbide, from the gas phase. Such powders are starting materials for high-performance ceramics.

The heteronuclear M₆S₈ cages A describe the structures of 1 and 2, which are formed from AgNO₃ and CuCl₂ or CuCl, respectively, ethanedithiolate (L), and [AuBr₂]^⊖. A homonuclear analogue of A is still unknown, since the combination of linear and trigonal-planar coordination is difficult to attain with a heavy element. The structure 3 can be regarded as a distorted sulfur icosahedron enclosing a likewise distorted silver cube with a further silver atom at the center.

Most likely, yes—at least, that is the answer based on the results of SCF calculations. The interconversion of the two equivalent bent equilibrium structures via the linear structure BOK requires an activation energy of only 2 kJ mol⁻¹, which is probably supplied by the zero-point vibrational energy.

Compound 1 may be viewed as a cyclic trimer of a tantalum nitride and provides support for the postulated stability of benzene-like metal nitride trimers. Compound 1 was obtained in 67% yield from [Cp^*TaCl₄] and N(SnMe₃)₃ and displays a six-membered ring, which, however, is not fully planar.

The amino(methylene)borane 1 can be complexed as an η² and as an η⁵ ligand. Whereas TiCl₄ coordinates in an η⁵ fashion to the five-membered ring (2) with transfer of a Cl atom to the B atom, reaction of 1 and Fe₂(CO)₉ gives compound 3 containing an FeBC ring; in 3, Fe is coordinated in a distorted trigonal-bipyramidal fashion.

Dissociative ionization of the tetrathiapentalenedione 1 and the dithiodiamide 2 affords the radical cation of ethylenedithione 3. C₂S can be neutralized in a collision experiment to give 3, whose existence has been predicted theoretically.

Analogous hexanuclear, paddlewheel complexes are formed by reaction of Ag^I and Cu^I precursors with the new ligand 3-tri-methylsilyl-2-pyridinethiol. MS₂N coordination has thus been achieved for the first time (see right, • = metal). The large Me₃Si group of the ligand prevents polymerization, which is observed for complexes of the parent compound. The ligand is accessible by silylation of 2-pyridinethiol.

A broad palette of organometallic compounds can be synthesized from the readily accessible 1, which exhibits two mutually reinforcing electrophilic centers, the isocyano unit and the halogenated α-C atom. The high synthetic potential of 1, as well as its 2-azaalleniumylidene and dichlorocarbene nature, are exemplified by preparation of 2–4.

A sixfold alkyl chain extension, the reaction of 1 with tBuOK and H₂CCHCH₂Br in THF to give 2, was achieved in one step in quantitative yield. The Fe^II center of 2 can be completely and reversibly reduced but not oxidized (with Br₂). Instead, bromine adds in a 1,3 fashion to all terminal CC bonds. The hexaalkylbenzene ligand can be released from 2 by irradiation. [Fe] = [(η⁵-C₅H₅)Fe]^⊕.

The title reaction 1a → 1b takes place between −78 and +55 °C, the rearrangement temperature depending on the substituents. The nitrile imines 1a can be characterized in solution by NMR and IR spectroscopy. Compounds 1a, E = SiMe₃ and SiPh₃, have also been trapped with methanol and with methyl acrylate (cycloaddition).

The unsaturated cyclic N,O-acetals 1 and 2 are promising starting materials for the synthesis of further valuable chiral intermediates. They were prepared from serine and threonine, respectively, by electrochemical decarboxylation. Acylation and addition reactions as well as catalytic hydrogenation were used to convert 1 and 2 into the mono-, bi-, and tricyclic compounds of type 3, in a regio- and stereoselective fashion.

The cluster anion 1 may be described as a weak complex of the fragment Mo(CO)₃ and [Fe₃S₄(SEt)₃]^3⊖. An Fe oxidation state of + 2.67 was determined for 1 from the isomer shift in the Mössbauer spectrum. This finding indicates the presence of Mo⁰ in 1. In agreement with this conclusion are the positions of the CO stretching frequencies in the IR spectrum of 1.

α-Elimination from 1 and thermal or photochemical cleavages of 2 produce tBu₂Si:, the trapping or subsequent products of which can be isolated in good to very good yields. The silanediyl generated from 1a by α-elimination does not dimerize to tBu₄Si₂, but instead produces the four-membered ring compound 3 in 15% yield.

The simplest π complex of SO₂ with an organic molecule—C₂H₄ · SO₂—was formed by ultrasonic expansion of a C₂H₄SO₂Ne gas mixture. The structure derived from the microwave spectrum reveals that the SO₂ and C₂H₄ planes are nearly parallel (C_s symmetry) and separated by 3.509 Å. The splitting pattern in the spectrum indicates the existence of a tunneling process between equivalent structures.

The first species having a partial structure, the E/Z-isomeric diphosphabutatriene derivatives 1, were prepared according to a synthetic principle similar to the Wittig-Peterson condensation. Compound 1 is a stable, yellow, crystalline compound.

The crystalline sodium salt of calix[4]arene-sulfonate 1 consists of alternating organic and inorganic layers. Double layers of the basketlike pentaanions alternate with layers of sodium ions and water molecules; the similarity with the structures of clays is readily apparent. Acetone is bound in the cavity of 1, the O atom projecting into the hydrophilic layer (see right).

Saturated seven-membered rings containing an O atom—oxepanes— are found increasingly in nature. A new, highly promising strategy for the synthesis of oxepanes 3 starts from the dithionoesters 1, which, upon irradiation, cyclize with loss of S₂ to give the olefins 2. Regioselective hydrolysis with tautomerization leads finally to the oxepanes 3.

4-Alkoxybenzyl alcohol resins are suitable supports for the solid-phase synthesis of O-glycopeptides. This was shown by the syntheses of the hexapeptides 1 and 2 in 55 and 48% yield, respectively, based on the first amino acid to be coupled. β-Elimination, racemization, or glycoside cleavage were not observed.

Yes and no could be the answer to the question posed in the title. Although it was not possible to detect the diazaferrocene 1, the complex 1 · 2 C₄Me₄NH was in fact isolated and characterized. It was formed according to reaction sequence (a).

The Swern oxidation is ideal for the transformation of strained cis-1,2-cyclo-pentanediols such as 1 to α-diketones such as 2. Compound 2, the valene of o-benzoquinone, is thus readily accessible. Its synthetic potential is demonstrated by the construction of other valenes, such as 3 (reaction of 2 with diaminomaleonitrile).

The title compound 2 is characterized by many interesting features: 2 is the first dilithiomethane stabilized by two boryl substituents; NMR and X-ray data establish its 1,3-diborataallene structure. In contrast to known dilithio-methane derivatives, which are aggregated, 2 is monomeric (R = 2,4,6-Me₃C₆H₂).

The synthesis of nitrogen heterocycles such as 1 and 2 from cyanogen and oxalyl halides is possible in one step and in yields of 60–70% with the catalyst system NRX^⊖/HX, X = Cl, Br. Compound 1 can be easily cleaved to give functionalized imidazoles, and 2 is of interest owing to its bactericidal activity as well as its possible use as a synthetic building block.

The cyclic s-trans-1,3-dienes 3 are novel, highly promising synthetic intermediates. They may be obtained easily and selectively from the cyclic ketovinyl sulfoxides 2. This photoreaction is surprising, for the compounds 1 react completely differently upon irradiation. The photoisomerization of 2 presumably occurs via the diradical 4 as intermediate.

The bond between the new protecting group 1 and the amino groups of amino acids is very acid stable. However, it can be easily and quantitatively cleaved under almost neutral conditions by Pd⁰ catalysis. Further advantages of the protecting group 1 are its strong UV absorption and its stability in the Rh^I-catalyzed cleavage of “normal” allyl protecting groups; in addition, the amino acids containing these protecting groups are almost always crystalline.

The chemical and electronic properties of tetrathiafulvalene (TTF) change appreciably when the molecule is bent. In the title compounds 1, R = OPr or OHex, such a structure is present. The cage compound 1 is readily accessible and the (solubility-improving) substituents R may be varied.

Can enantiomerically pure oligooxymethylene helices induce chirality by means of stereoelectronic effects? This question was investigated by use of the model compounds 1, n = 1–4. The asymmetric induction—determined by nucleophilic methylation—occurred in the same direction in all cases. This finding indicates that paraformaldehyde may have been involved in the amplification of chirality during the course of chemical evolution.

Phosphorylphosphane complexes 1 are the ideal starting compounds for the preparation of “phospha-Wittig” reagents 2, which react with aldehydes and ketones to give the corresponding phosphaalkene complexes 3. These can be isolated directly or after trapping with, for example, MeOH or cyclopentadiene. Liberation of the phosphaalkene from 3 should also be possible. R = Me, Ph.