Alkylaluminium compounds, reactions with

HL3 and HL4 were also reacted with [Ln N(SiHMe2)2 3(THF)2] via amine elimination to form the corresponding mono(aminopyridinato) complexes (Ln = Y (14 and 15), La (16 and 17)). Complexes 14-17 are not active for the polymerization of ethylene in the presence of alkylaluminium compounds. The reactions of the mono(aminopyridinato) complexes with aluminum compounds AlEts or AIH/BU2 showed a fast aminopyridinato ligand transfer to the aluminum atom. The products of the transfer reaction are aminopyridinato-stabilized dialkylaluminium compounds. The catalytic activity was believed to be prohibited by the ligand transfer reaction (Scheme 5) [41]. 

These kinetic features parallel very closely those already proposed by Tait and co-workers. The Yermakov scheme is based on evidence - arising from kinetics and active centre concentration determinations ( CO tagging with PHj addition to prevent copolymerization). These investigations demonstrated that the value of the rate constant for propagation did not depend on either the nature of the alkylaluminium compound (cf. ref. SO) or on the composition of the TiClj sample. Also, the effective activation energy, Eett, of the overall polymerization process in the presence of TiClj was higher than that of the propagation reaction, Ep, such that... 

This reaction is very limited in scope, but gives some useful products. It works well with methyl and ethyl halides, the chlorides being much the most important as they are so much cheaper than bromides and iodides. Aluminium generally needs activating, and one of the most effective ways is by means of some preformed alkylaluminium compound, though iodine or AICI3 can also be used. Phenylaluminium sesquichloride is formed, only with difficulty, when PhQ reacts with aluminium which has been... 

The reaction takes place at low temperature (40-60 °C), without any solvent, in two (or more, up to four) well-mixed reactors in series. The pressure is sufficient to maintain the reactants in the liquid phase (no gas phase). Mixing and heat removal are ensured by an external circulation loop. The two components of the catalytic system are injected separately into this reaction loop with precise flow control. The residence time could be between 5 and 10 hours. At the output of the reaction section, the effluent containing the catalyst is chemically neutralized and the catalyst residue is separated from the products by aqueous washing. The catalyst components are not recycled. Unconverted olefin and inert hydrocarbons are separated from the octenes by distillation columns. The catalytic system is sensitive to impurities that can coordinate strongly to the nickel metal center or can react with the alkylaluminium derivative (polyunsaturated hydrocarbons and polar compounds such as water). 

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