Alkylaluminum cocatalysts

In the polymerization of butadiene, Teyssie (52-54) has shown that certain electron donors, such as alcohols or phosphines, can convert tt-allylnickel chloride from a catalyst which forms c/j-polybutadiene to one which produces frans-polybutadiene. These ligands presumably block a site on the nickel atom, forcing the butadiene to coordinate by only one double bond. While alcohols cannot be added directly to the hexadiene catalyst (as they deactivate the alkylaluminum cocatalysts), incorporation of the oxygen atom on the cocatalyst places it in an ideal position to coordinate with the nickel. The observed rate reduction (52) when the cri-polybutadiene catalyst is converted into a fra/w-polybutadiene catalyst is also consistent with the observed results in the 1,4-hexadiene synthesis. 

In the literature there are many reports of the formation of active catalyst for the 1 1 codimerization or synthesis of 1,4-hexadiene employing a large variety of Co or Fe salts, in conjunction with different kinds of ligands and organometallic cocatalysts. There must have been many structures, all of which are active for the codimerization reaction to one degree or another. The scope of the catalyst compositions claimed to be active as the codimerization catalysts is shown in Table XV (69-82). As with the nickel catalyst system discussed earlier, the preferred Co or Fe catalyst system requires the presence of phosphine ligands and an alkylaluminum cocatalyst. The catalytic property can be optimized by structural control of these two components. 

Olefin Polymerizations and Copolymerizations with Alkylaluminum-Cocatalyst Systems... 

Figure 2. Effect of alkyl size in tri-n-alkylaluminum cocatalyst on activity as measured by bottle polymerization rates...

Figure 7. Effect of groups in alkylaluminum cocatalyst on activity of aged catalyst preparations X—diisobutylaluminum chloride catalysts aged for five weeks at room temperature.

When [Tl(Tpx)] (Tpx = TpMs or TpMs ) reacts with NiCl26H20, [NiCl(TpMs)] and [NiCl(TpMs )] are formed in good yields. [NiCl-(TpMs )] undergoes an isomerization process, giving [NiCl(TpMs )]2 (TpMs = HB(pzMs)(pz5Ms)2. Treatment of [NiCl(TpMs)] and [NiCl(TpMs )] with alkylaluminum cocatalysts such as MAO and trimethylaluminum in toluene generates active catalysts for ethylene oligomerization.169... 

Oligomerization and polymerization catalysis by metal complexes comprises three steps initiation, propagation, and termination. Chain growth proceeds at a coordinatively unsaturated see Coordinative Saturation Unsaturation) center having a metal-carbon or metal-hydride see Hydride Complexes of the Transition Metals) bond, usually generated by the interaction of a metal complex with an activating species such as an alkylaluminum cocatalyst. The first insertion of an alkene monomer into the metal-carbon or metal-hydride bond (chain initiation) is followed by repeated insertions... 

Alkylaluminum cocatalysts such as AlMea and MAO generate less active catalysts (1—8 kg PE/mol... 

Titanocene- and zirconocene-catalyzed alkene polymerization involves initial alkyl group transfer from alkylaluminum cocatalyst to Ti or Zr centers and subsequent multiple insertion of monomer into the metal-carbon bond. Zr complex catalyzed carbomagnesation shown in Eq. 5.33 [128-136] also involves alkyl ligand transfer between the main group metal and Zr. 

Supported metallocene catalysts were combined with KIO montmorillonite by Weiss et al. During preparation of the clay, bentonite was treated with mineral acid, causing some of the octahedral alumina sheet to dissolve. This created dendritic silica, whose hydroxyl termination served to immobilize an alkylaluminum cocatalyst (either AlMes or Al Bus). The supported cocatalysts activated the simple metallocene dichlorides II and XI,... 

Lieber, S. Brintzinger, H.-H. Rropene polymerization with catalyst mixtures containing different an a-zirconocenes Chain transfer to alkylaluminum cocatalysts and formation of stereoblock polymers. Macromolecules 2000,33, 9192-9199. 

AIR3 = alkylaluminum cocatalyst R = alkyl group (methyl, ethyl)... 

Early studies [103-110] on spectroscopies and kinetics predicted the formation of (alkyl) titanocene complexes (Cp2Ti(R)Cl) (R=Me or Et) by ligand exchange reaction of alkylaluminum cocatalyst... 

Xia W, Liu B, Fang Y, et al Multinuclear soHd-state NMR smdy of the coordinative nature of alkylaluminum cocatalyst on PhrUips CrOx/Si02 catalyst, Appl Catal A Gen 389(1-2) 186-194, 2010. 

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