Klaus Mehler

Metallotropie des allylmagnesiums; Struktur und NMR-linienformanalyse von cyclopentadienyl(2-methylallyl)-magnesium

Abstract Low temperature 1H and 13C NMR spectra at 9.4 T of cyclopentadienyl(2-methylallyl)magnesium (1) dissolved in THF confirm that the allyl group is σ-bonded to Mg. 1 is fluxional: in THF solutions for the equilibration of the terminal allyl-carbon atoms the activation parameters Ea 13.0 kcal/mol and ΔS≠ +6.5 e.u. were obtained by line shape analysis of the 13C1H spectra. The mechanism of rearrangement is discussed.

Deposition of Aluminum–Magnesium Alloys from Electrolytes Containing Organo-Aluminum Complexes

Organo-aluminum compounds have been used for many years as electrolytes in the coating industry. In this communication the development of a galvanic process for generating aluminum-magnesium coatings from organometallic electrolyte systems is reported as well as results on physical properties like adhesion, ductility and corrosion resistance. (orig.)

Elektrolytische Abscheidung von Aluminium-Magnesium-Legierungen aus aluminiumorganischen Komplexelektrolyten

Anknupfend an die Weiterentwicklung der galvanischen Reinaluminium-Abscheidung aus fluoridhaltigen, aluminiumorganischen Elektrolyten ist es jetzt erstmalig gelungen, Aluminium und Magnesium aus Toluollosungen von halogenfreien, aluminiumorganischen Komplexelektrolyten abzuscheiden. Die Magnesium-Einbauraten sind durch entsprechende Zusammensetzung der Aluminium-Magnesium-Legierungsanoden oder durch getrennte anodische Aluminium- bzw. Magnesium-Stromkreise in einem weiten Bereich wahlbar. Die anodischen sowie kathodischen Stromausbeuten liegen bei 100%. Die erhaltenen Schichten sind optisch ansprechend und liegen je nach Magnesiumgehalt bzw. angewendeter kathodischer Stromdichte mit seidenmatter bis glanzender Oberflache vor. Elektronenmikroskopische Untersuchungen zeigen im Gegensatz zur Reinaluminiumabscheidung eine deutliche Kugelstruktur. Die Aluminium-Magnesium-Schichten sind hervorragend als Schutz gegen Kontaktkorrosion an Magnesiumbauteilen geeignet. Elektrochemische Untersuchungen zeigen z. B. bei einer Magnesium-Einbaurate von ca. 25 Gew.-% ein ausgepragtes Passivitatsintervall gegenuber der Legierung AZ91hp. Praxisorientierte Untersuchungen in zyklischen Korrosionstests (simulierte 10 Jahre Feldbelastung) zeigen im Vergleich zu galvanisch verzinkten und zusatzlich silikatisch versiegelten Testschrauben keinerlei Korrosion. Electrolytic Deposition of Aluminium-Magnesium-Alloys from Electrolytes Containing Organo-Aluminium Complexes The galvanic deposition of pure aluminium from fluoride-containing electrolytes has been developed further and for the first time aluminium and magnesium have been deposited from a toluene-solution of a halide-free organo-aluminium complex electrolyte. The rate of incorporation of magnesium can be controlled over a wide range by either adjusting the composition of the aluminium-magnesium anode or by using separate aluminium or magnesium anodic circuits. The current efficiency for both anode and cathode approaches 100%. The resulting coating is optically attractive and, depending upon the magnesium-content or the cathodic current density, can be formed as a dull or polished surface. Investigations using an electron microscope show that the surface, in contrast to that of pure aluminium, consists of spherical particles. The aluminium-magnesium coating provides excellent protection against the corrosion of magnesium components. Electrochemical investigations using, for example 25% by weight magnesium incorporation, indicate a pronounced passivity interval compared to the alloy AZ91hp. In contrast to galvanic zinc-plated and silicate-sealed examples, cyclic corrosion tests on screws simulating 10 years of exposure, show no corrosion.

Strukturvergleich bei 9,10-Dihydro-9,10-anthrylen-Verbindungen des Magnesiums und des Alkylaluminiums / Comparison between the Structures of 9,10-Dihydro-9,10-anthrylene Compounds of Magnesium and Alkylaluminium

In magnesium as well as in aluminium derivatives of anthracene (1−4, 8) and its trimethylsilyl derivatives (5, 6 and 11), the metals occupy the axial positions at C9 and CIO, to form five-, seven- or ten-membered metallacycles, respectively, in 1−3, 5, 6 and 11. It appears that the metalla-ring size, and thus the coordination geometry of the bridging metal is of influence upon the chemical behaviour.

The Cooperate Effect of Organomagnesium and Nickel Compounds in the Catalytic Oligomerization of 1.3-Dienes

Crotylmagnesiuin halide and nickelocene (molar ratio Mg/Ni~100) catalyze the dimerization of butadiene to 3-methyl-1.4.6-heptatriene arid the triroerization to 1-exo-methylene-2-methyl-4.6-divinyl-cyclohexane. Isoprenylmagnesiuinhalide and nickelocene catalyze the dimerization of isoprene to a mixture of 3.3.6- and 2.3.6-trimethyl-1.4.6-heptatriene. On the basis of model reactions, the catalytic processes are suggested to occur through a sequence of Mg-C addition to C=C, exchange of allyl groups between Mg and Ni followed by displacement reactions in CpNi-П-allyl complexes or CpNi-alkyl intermediates by the 1.3-diene.