Synthesis and ligand exchange reactions of P2Pd(II) and P2Pt(II) salicylaldimates

Reaction of (dppe)MCl(2)(dppe = 1,2-bis(diphenylphosphino)ethane) with 2-(N-phenyliminomethyl)phenol leads to air-stable (dppe)M(N,O) chelates (M = Pd, 1a; M = Pt, 1b). The N-4-methylphenyl derivative of 1a has been characterized by X-ray analysis. The N,O ligands are kinetically labile and exchange occurs in solution in the presence of other salicylaldimines. In the presence of anilines, a metal-mediated imine exchange process occurs. Hammett analysis reveals that the platinum complexes are sensitive to the electronics at N but not at O. Electron donating groups on the N-aryl ring stabilize the metal complex.     

Manual construction and mathematics- and computer-aided counting of stereoisomers. The example of oligoinositols

Two methods to obtain numbers of stereoisomers and of achiral stereoisomers of a given molecular structure are detailed on the example of di- and triinositols. The first method is manual exhaustive construction free of redundance of all stereoisomers, which is rendered feasible by symmetry considerations despite the large number of isomeric triinositols (82176). The second method is counting without constructing, made possible by use of a mathematical tool, the Cauchy-Frobenius lemma, which actually is a formalized manner of considering symmetry. The results are compared to those obtained by computer-aided stereoisomer generation using the program MOLGEN 3.5. It is demonstrated that in their results all three methods agree.     

Untersuchungen an zeolithischen Heptagermanaten mit Hilfe der Kernresonanzmethode

Zusammenfassung Zeolithische Heptagermanate der FormelMe ₃HGe₇O₁₆ ·x H₂O (Me=Li, K, Rb, Cs, Tl) mit verschiedenem Wassergehalt (x=0–6) wurden röntgenographisch, thermogravimetrisch und mit Hilfe von Kernresonanzmessungen bei verschiedenen Temperaturen untersucht. Während bei Raumtemp. der Großteil der Wassermoleküle beweglich ist, frieren diese Bewegungen bei Erniedrigung der Temperatur allmählich ein. Außerdem zeigen die Resonanzen einen Anteil, der isolierten Protonen zuzuordnen ist.

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NMR studies on zeolitic heptagermanates

Zeolitic heptagermanates with compositionMe ₃HGe₇O₁₆ ·x H₂O (Me=Li, K, Rb, Cs, Tl;x=0–6) were studied by means of X-ray, thermogravimetric and NMR measurements at various temperatures. At room temperature the largest part of the water molecules is mobile. The motion of these molecules is frozen in continuously by lowering the temperature. The resonances do also exhibit a part which can be correlated to the presence of isolated protons.

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Mit 8 Abbildungen     

KEu(CH3COO)3, das erste ternäre Europium(II)-acetat

KEu(CH₃COO)₃, the First Ternary Europium(II) Acetate On of EuCl₂ with a melt of dry potassium acetate yields pale greenish-yellow single crystals (300°C, sealed glass ampoule, EuCl₂ and K(CH₃COO) in a molar ratio of 1 : 3). The crystal structure determination (orthorhombic, P2₁2₁2₁ (no. 19), Z = 8, a = 1166.3(1) pm, b = 1288.4(2) pm, c = 1493.9(2) pm, R = 0.043, R_w = 0.032) revealed the composition KEu(CH₃COO)₃. The structure consists of one-dimensional chains built up by bridging acetate groups in the [100] and [001] directions in which potassium and europium alternate as central atoms. Eu²⁺ is surrounded by nine and eight and K⁺ by seven and six oxygen atoms, respectively. These chains are linked in the [010] direction so that a three-dimensional network is formed. The high coordination numbers of the acetate oxygen atoms of up to four are remarkable. Therefore, the acetate groups have highly bridging functions in addition to their chelating coordination of the cations.     

Polylithiumorganische Verbindungen: XVII. Splatung von 1,1′-Bicyclopropyliden (butterfly olefin) mit Lithiumpulver zu 1,6-Dilithio-3-hexin über (1,3-Dilithiopropyliden)cyclopropan als isolierbare Zwischenstufe

While for the reductive cleavage of a cyclopropane σ-bond usually two lithium atoms are necessary, with the same amount of lithium two σ-bonds of the “butterfly olefin” 4 are cleaved. On the way to 1,6-dilithio-3-hexyne (7) (1,3-dilithiopropylidene)cyclopropane (8) can be isolated provided that diethyl ether is used as the solvent.     

Thermooxidative degradation of compositions based on an epoxy oligomer

The work is devoted to studying the nonisothermal thermooxidative degradation of the composition of an epoxy oligomer cured with 4,4-diaminodiphenyl sulfone in a stoichiometric ratio of 30 wt % hardener per 70 wt % oligomer. The relationship between the structure of the composition and the kinetic parameters of the thermooxidation is established. The network structure was varied by changing the temperature and curing time. Specific features of the mechanism and kinetics of the nonisothermal degradation epoxyamine polymer are determined using the thermoanalytical method, namely, differential scanning calorimetry, and analysis of the oxidation products. The composition of the products, the values of the activation energy and preexponential factor for the reactions occurring in the nonisothermal mode at different rates of heating of samples with different structures of the network, showed that their mechanism is controlled by a time-temperature superposition. The rate of heating of the sample determines the participation of bonds of internodal links and network nodes at different stages of the overall process. An increase in the density of the network leads to a decrease in the rate of the thermooxidative degradation of internodal chains and an increase in the rate of decay of network nodes.     

Polylithiumorganic compounds. Part 29: C,C Bond cleavage of phenyl substituted and strained carbocycles using lithium metal

The reaction of phenyl substituted cyclopropanes phenylcyclopropane and 1,1-diphenylcyclopropane, phenyl substituted bicyclobutanes 1-phenylbicyclobutane, 1-methyl-3-phenylbicyclobutane, 1-methyl-2,2-diphenylbicyclobutane, as well as phenyl substituted spiropentanes phenylspiropentane and 1,1-diphenylspiropentane with lithium metal or lithium di-t-butylbiphenyl (LiDBB) was investigated. Under suitable reaction conditions and choice of solvent in all cases cleavage of the single bond next to the activating phenyl group was observed. The dilithiumorganic compounds thus obtained are sufficiently stable and can be trapped with electrophiles. Lithium hydride elimination is observed as follow-up reaction only in a few cases. The corresponding anions of the strained ring systems 1-lithio-2,2-diphenylcyclopropane, 1-lithio-3-phenylbicyclobutane, 1-lithio-3-methyl-2,2-diphenylbicyclobutane, and 1-lithio-4-phenylspiropentane, which can be obtained by lithium bromine exchange or by metalation of the unsubstituted carbocycle, do not show any cleavage upon reaction with lithium metal.