Trialkyl aluminium

Chirales Trialkyl-aluminium ist fur asymmetrische Reduktionen von Bedeutung6, und Alkoxy-aluminium-hydrid als selektives Reduktionsmittel7 (s.S.337 u. 416). 

Aus zwei Aquivalenten Benzonitril werden mit Trialkyl-aluminium und Tetrachlor- bzw. Te-trabrommethan 2-substituierte 4,5-Diphenyl-imidazole erhalten (s.Bd. XIII/4, S. 250). Zur Umsetzung von Blausaure in fliissigem Ammoniak zu 4,5-Dicyan-imidazol s. Bd. E5/2, S. 1555. 

Besonders interessant sind die hohen Konstanten von Trialkyl-Aluminium, die auf die Offnung von C-Al-Bindungen zuriickzufiihren sind. 

Usually the Zigler-Natta co-ordination initiator system is used to graft oc-olefins onto other polymers to give stereo block/graft copolymers, which contain isotactic/atactic sequences. In the Zigler-Natta co-ordination catalyst [69] system, the diethyl aluminium hydride reacts with pendant groups to form macromolecular trialkyl aluminium. The residual initiator is freed by extraction methods. 

A catalyst system composed of neodymium chloride/trialkyl aluminium is presumed to give living polymer of butadiene containing cis-1,4 units higher than 98%. This living... 

Dialkyl-beryllium und Trialkyl-aluminium bilden in der Haupt-sache dimere Assoziate. Trialkylaluminium mit voluminosen Resten, z. B. A1(CH2 CHRR)3 (Iso-butyl-Typ), ist dagegen praktisch uberhaupt nicht assoziiert 16). 

Katalysatorsystem Kobalt Oder Nickel- verbindungen/ Alkylaluminium-chloride ) Jodhaltige Titan-verbindungen/ Trialkyl-aluminium- verbindungen ) Nickel- verbindungen / Trialkyl-aluminium-verbindungen/ Borfluorid )... 

Synthesis of linear polyethylene and coordinate polymerisation (combination of trialkyl aluminium and titanium chloride as catalyst) by Ziegler Isotactic and syndiotactic polymerisation (polypropylene and polydienes) discovered by Natta... 

In reactions requiring palladium 0), formation of the active complex may be achieved more conveniently by reduction of a palladium(ll) complex, for example, Pd 0Ac)2- Any phdsphine may then be used in the reaction, without the need to synthesize and isolate the corresponding palladium 0)-phosphine complex. Only 2-3 equivalents of phosphine may be needed, making the palladium(O) complex coordinatively unsaturated and therefore very reactive. The reduction of palladium li)to palladium(o) can be achieved with amines, phosphines, alkenes, and organometailics such as DIBAL-H, butyl lithium, or trialkyl aluminium. The mechanisms are worth giving as they illustrate the basic steps of organometallic chemistry. 

By 1950 Ziegler had worked on the growth of alkyl chains by insertion of ethylene into the Al—C bond of trialkyl-aluminium, mainly focused in the field of polyethylene. Natta, from the beginning, attempted propylene polymerization, succeeding in... 

Polymerization of MMA with -C4H9Li in toluene at -78°C gave isotactic-rich PMMA with a broad but unimodal MWD.69,348 Addition of trialkyl-aluminium to -C4H9Li changes the initiator activity for MMA to syndio-... 

Auch Metallsalze wie Kupfer(I)-chlorid3, Antimon(III)-chlorid4 oder Uranyl-Verbin-dungen5 kommen als Katalysatoren in Frage. Praparativ und theoretisch interessant sind die cis-trans-Isomcrisierungen mit Tefcraalkyl-zinn-8 und Dialkyl- bzw. Trialkyl-aluminium-Verbindungen7. 

Alkyl aluminium hydrides are obtained by reaction 18.29. These compounds, although unstable to both air and water, are important catalysts for the polymerization of alkenes and other unsaturated organic compounds. Ziegler-Natta catalysts containing trialkyl aluminium compounds are introduced in Box 18.3. 

The author was interested in how much the conductivity of oriented polyacetylene films can be enhanced by stretching compared with that of as-grown films. Polyacetylene films were prepared by using both trialkyl aluminium and tetraalkyl titanate having long alkyl chains. Orientation and conductivity of stretched polyacetylene films have been reported here. 

Polyacetylene films were synthesized by a non-solvent polymerization method using a thermally aged Ziegler catalyst of trialkyl aluminium and tetraalkyl titanate [7]. Trialkyl aluminiums used were Trihexyl aluminium. Trioctyl aluminium and Tridecyl aluminium. Tetraalkyl titanates used were Tetrahexyl titanate. 

Table 1 Stretching ratio of polyacetylene films prepared by catalysts of trialkyl aluminium and tetraalkyl titanate.

Electrical conductivity of polyacetylene films depends on orientation of polymer chains. Figure 5 shows the relationship between relative electrical conductivity and dichroic ratio of polyacetylene films prepared by a mixture catalyst of Trihexyl aluminium and Tetradecyl titanate. Conductivity of fully stretched or oriented polyacetylene films showed twenty times higher than that of as-grown films. Conductivity of polyacetylene films, prepared by other catalysts systems of trialkyl aluminium and tetraalkyl titanate, showed similar relationship, although increment of the conductivity was lower. 

A general method of preparation of alkyl phosphonous dihalides is the reaction of phosphorus trihalide with a dialkyl mercury, a dialkyl cadmium or a trialkyl aluminium. 

The trialkyl aluminiums are strong Lewis acids and coordinate with electron donors to form complexes in which aluminium acquires a stable octet of electrons, as in the complexes above. The trialkyl aluminiums show a stronger tendency to complex formation than do the trialkyls of B, Ga, In or H. 

Trialkyl aluminium complexes with various degrees of stability are formed with phosphines, phosphine oxides, phosphites, phosphonates and phosphinates as well as with amines and other non-phosphorus ligands (9.130). 

Cyclophosphinoalanes can be obtained by heating the appropriate trimethyl aluminium-secondary phosphine adduct (or the trialkyl aluminium with the phosphine) (9.138, 9.139). If higher temperatures are used, glassy polymeric materials such as (Me2P-AlMe2) may be obtained. 

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