Buchbesprechungen

Ohne Zusammenfassung     

The aromatic diboracyclopropenyl (diboriranyl) anion; CB2H3 −: An ab initio study

The most stable structure of CB₂H₃ ^–, as established computationally, is the aromatic diboracyclopropenyl (diboriranyl) anion (5), while open-chainC _2v, isomer H₂BCBH (7) is only 3 kcal/mol higher in energy at the QCISD(T)/6-311 +G^**//MP2/6-31+G^*+ZPE (HF/6-31 +G^*). The 47-kcal/mol barrier between cyclic,5, and open-chain,7, structures suggests that both of them may be observed. The aromatic stabilization energy of the diboriranyl anion (18 kcal/mol) is half the value in the isoelectronic cyclopropenium ion, C₃H₃ ⁺. The computed, by IGLO method (5a), and experimental (6a) chemical shifts,(¹³C) and(¹¹B), agree within 4 ppm range. The theoretical vibrational frequencies of the most stable isomers,5 and7, are presented for experimental verification of these species.     

Theoretical investigation of the apparently irregular behavior of pt-pt nuclear spin-spin coupling constants

One-bond Pt-Pt nuclear spin-spin coupling constants J(Pt-Pt) for closely related dinuclear Pt complexes can differ by an order of magnitude without any obvious correlation with Pt-Pt distances. As representative examples, the spin-spin couplings of the dinuclear Pt(I) complexes [Pt(2)(CO)(6)](2+) (1) and [Pt(2)(CO)(2)Cl(4)](2-) (2) have been computationally studied with a recently developed relativistic density functional method. The experimental values are (1)J((195)Pt-(195)Pt) = 5250 Hz for 2 but 551 Hz for 1. Many other examples are known in the literature. The experimental trends are well reproduced by the computations and can be explained based on the nature of the ligands that are coordinated to the Pt-Pt fragment. The difference for J(Pt-Pt) of an order of magnitude is caused by a sensitive interplay between the influence of different ligands on the Pt-Pt bond, and relativistic effects on metal-metal and metal-ligand bonds as well as on "atomic orbital contributions" to the nuclear spin-spin coupling constants. The results can be intuitively rationalized with the help of a simple qualitative molecular orbital diagram.     

Ueber die Bestimmung des Gerbstoffs in Gerbstoffmaterialien

Ohne Zusammenfassung     

Über Erdalkalimetalloxothallate. II. Darstellung und Kristallstruktur von Ba2Tl2O5

On Alkaline Earth Metal Oxothallates. II. Preparation and Crystal Structure of Ba₂Tl₂O₅ Ba₂Tl₂O₅ was prepared and investigated by X-ray single crystal methods (space group D? Pcmn, a = 6.264, b = 17.258, c = 6.05 Å) Ba₂Tl₂O₅ is isotypic with Ca₂Fe₂O₅.     

Über die Struktur von Bis-(dihydroxoboroxalendiamiddioximato)-nickel(II)-tetrahydrat

The space group of the sparingly soluble brown coloured bis-(dihydroxobor-oxalene-diamide-dioximato)-nickel(II)-tetrahydrate (C₄H₁₂N₈O₈B₂Ni · 4 H₂O) is P21/c with a = 9.25, b = 13.27, c = 6.61 Å and β = 92.7°. The structure was solved on single crystals. There are two molecules in the unit cell. Within the square planar complex the nickel atom is bonded to the four nitrogen atoms of the plane system of the two dioximato ligands (Ni? N = 1.84 ± 0.02 Å). Each of the boron atoms is tetrahedrally surrounded by two oxygen atoms belonging to the oxime groups and two hydroxyl groups (B? O = 1.50 ± 0.06 Å). Thus the complex has the conformation of a chair form. The water molecules participate in intermolecular hydrogen bonds. There is no interaction between Ni atoms.     

Kombination wirksamer Trennverfahren mit modernen analytischen Methoden in der Naturstoffchemie

Zusammenfassung Aus Crotonöl konnten durch Anwendung multiplikativer Verteilungs- und chromatographischer Verfahren die entzündlichen und cocarcinogenen Substanzen A1–A4 und B1–B7 rein dargestellt werden. Diese Substanzen sind Diester des polyfunktionellen Diterpenalkohols Phorbol, C₂₀H₂₈O₆ mit jeweils einer kurzkettigen (Essig-, (+)-S-2-Methylbutter-, Tiglinsäure) und einer langkettigen Fettsäure (Capryl-, Caprin-, Laurin-, Myristin-, Palmitinsäure). Die Teilsynthese einiger Substanzen wird angegeben. Aus den UV-, IR- und KMR-Daten und chemischen Befunden werden Teilformeln für Phorbol abgeleitet und diskutiert.

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Summary The compounds A1–A4 and B1–B 7 have been isolated from croton oil in pure state by multiplicative distribution and chromatography. These compounds are di-esters of the polyfunctional diterpene alcohol phorbol C₂₀H₂₈O₆ each with a short chain (acetic-, (+)-S-2-methyl-butanoic-, tiglic acid) and a long chain fatty acid (octanoic-, decanoic-, dodecanoic-, tetradecanoic-, hexadecanoic acid). The partial synthesis of some compounds is described. From ultraviolet-, infrared-, nmr-spectra and from chemical evidence partial structures for phorbol are being discussed.

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Für die Messung von KMR-, Massen- und CD-Spektren und anregende Diskussionen danken wir den Herren Dr. J. Sonnenbichler, München, Dr. J. Jochems, Heidelberg, Dr. A. Mannschreck, Heidelberg, Dr. H. Budzikiewicz, Braunschweig, Dipl.-Chem. C. Wünsche, Heidelberg, Doz. Dr. G. Snatzke, Bonn, und V. Scheidel, Heidelberg.

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Vorgetragen von H. Kubinyi.     

Stereospecific Synthesis of (E,E)-9, 11, 13-Tetradecatrienyl Acetate and Aldehyde (Geometrical Isoers of the Major Components of Two Sex Pheromones of Lepidoptera)

A stereospecific synthesis of (E,E)-9, 11, 13-tetradecatrienyl acetate and aldehyde is described. The key steps are two sequential palladium-catalyzed cross-coupling reactions between adequate organometalic reagents and the (E)-1,2-dibromoethylene.