Alkylaluminums oxygenation

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. 

Caut/on Alkylaluminum reagents must be handled under total exclusion of atmospheric oxygen and moisture (see Example 3-28). 

On account of the sensitivity of the catalysts to traces of moisture or oxygen, it is generally not suitable to operate with lower concentrations of alkylaluminum, because the latter acts also as a protector of the solid catalyst. However, by operating with very pure solvents and reagents, the concentration of A Rz can be reduced to lower values (10 — 10 mol/1.). 

However, Natta, Pasquon, Zambelli and Gatti (63) have shown that titanium trichloride-dialkylaluminum chloride or titanium trichloride and alkylaluminum dichloride with nucleophilic materials are good catalysts for the polymerization of propylene to the isotactic structure. The titanium trichloride could also be made in situ from titanium tetrachloride and triethyl aluminum. Vesely, Ambroz, Vilin and Hamrik (64) showed the addition of the nucleophilic materials to diethylaluminumchloride-titanium trichloride polymerizations decreased the rate of polymerization and changed the stereospecificity. The more nucleophilic materials such as sulfur compounds were more effective than the less nucleophilic oxygen materials. 

Ethylene CH2=CH2 Acetylene, Cu,Fe,Al,W, Pt, petr oil Air (Oxygen) plus Ethylene Vap Limits Lo-2.75-4.1% Hi-13.7-36.3% < 100mm (vacuum) 500- 700 No sparks. Ethylene content over 25%, No Oxygen, and use of inert gas blanket 450 Use of Alkylaluminum compds... 

In 1992 Kobayashi et al. [47] reported the first catalytic and enantioselective cyclo-propanation using the Furukawa modification [48] of the Simmons-Smith reaction of allylic alcohols in the presence of a chiral bis(sulfonamide)-Zn complex, prepared in-situ from the bis(sulfonamide) 63 and diethylzinc. When cinnamyl alcohol 62 was treated with EtgZn (2 equiv.), CHgIg (3 equiv.), and the bis(sulfonamide) 63 (12 mol %) in dichloromethane at -23 °C, the corresponding cyclopropane 64 was obtained in 82 % yield with 76 % ee (Sch. 26). They proposed a transition state XXIII (Fig. 5) in which the chiral zinc complex interacts with the oxygen atom of the allylic alkoxide and the iodine atom of iodomethylzinc moiety. They also reported the use of the bis(sulfonamide)-alkylaluminum complex 65 as the Lewis acidic component catalyzing the Simmons-Smith reaction [49]. 

In commercial polyethylene operations, poisons may enter the process as trace (ppm) contaminants in ethylene, comonomer, hydrogen (CTA), nitrogen (used as inert gas), solvents and other raw materials. These poisons reduce catalyst activity. Most damaging are oxygen and water. However, CO, CO, alcohols, acetylenics, dienes, sulfur-containing compounds and other protic and polar contaminants can also lower catalyst performance. With the exception of CO, aluminum alkyls react with contaminants converting them to alkylaluminum derivatives that are less harmful to catalyst performance. Illustrative reactions of contaminants with triethylaluminum are provided in eq 4.9-4.11 ... 

Caution. Alkylaluminum compounds, products, and the by-products of this reaction are extremely air sensitive and must be handled in a rigorously oxygen-free atmosphere. 

First they treat such an olefin with an organoaluminum compound, obtaining the primary alkylaluminum then oxidation with air or oxygen leads to an aluminum alkoxide which on hydrolysis gives the primary alcohol, e.g. ... 

A similar catalyst based upon W(CO)6 was studied by Warwel and Buschmeyer/ " Adding isobutylaluminum and oxygen to the catalyst effected a 50% conversion of 3-heptene. Upon recycling the catalyst, the activity decreased dramatically. The tungsten was displaced from the polymer by the alkylaluminum compound, and the tungsten complex then performed as a homogeneous catalyst (see Table 10). 

Isotactic polymers can be obtained by the use of (Et)2AlCl, and other mixed alkylaluminum halides give crystalline polymers [77], One report asserts that the latter catalysts are effective only in the presence of a proton-active cocatalyst such as water or hydrochloric acid [78]. Sulfuric acid has been used as a cocatalyst for Al(/-Pr)3 to give stereoregular poly(vinyl 5 c-butyl ether) and poly(vinyl 2-methylbutyl ethers) [79]. Furukawa has also reported the use of diethylzinc with either oxygen, water, or alcohols as cocatalysts to give stereoregular poly(vinyl ethers) [80]. 

In general this reaction is very facile and is proposed to occur via an intermediate Lewis acid-base complex, i.e., AIRaOHL). Such alkylaluminum complexes with oxygen-based Brpnsted acids (e.g., H2O, HOR, and HO2CR) are very unstable... 

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