Dialkylaluminum halide

Dialkylaluminum halides, alkylaluminum dihalides, and alkylaluminum sesquihalides will be referred to henceforth as alkylaluminum halides. ... 

Chlorine, bromine, and iodine act as cationogens in the presence of the more active Lewis acids such as trialkylalumi nu tn or dialkylaluminum halide [DiMaina et al., 1977 Magagnini et al., 1977]. The initiating species is the halonium ion X+ present in low concentration via the equilibrium reaction between Lewis acid and halogen. 

Recently, Kunz reported that dialkylaluminum chlorides add in a 1,4-mode to N-(a,f3-unsaturated acyl)oxazolidones (9 Scheme 3),12 while high enantioselectivity is obtained with the chiral N-(a, 3-un-saturated acyl)oxazolinone (11). Typically, higher dialkylaluminum halides (R = ethyl, isobutyl) do not... 

The catalyst for the reaction between PVC and the high cis-1,4-polybutadiene was a dialkylaluminum halide—e.g., Et2AlCl—or sesquihalide. The catalyst could be added from an external source or could be generated in situ—e.g., by the reaction of an aluminum alkyl with either titanium tetrachloride or a reactive organic halide such as benzyl chloride or tert-butyl chloride. The concentration of Et2AlCl was varied from 0.2-5% by weight based on PVC, although the preferred concentration was between 0.5 and 1.5 wt %. 

A Theory of Initiation and Propagation of Carbonium Ion Polymerizations with Trialkylaluminum Catalysts. Trialkylaluminums or dialkylaluminum halides in conjunction with suitable cocatalysts in polar solvent are active polymerization catalysts. For example, when cocatalytic amounts of tert-butyl chloride are added to a quiescent mixture of trialkylaluminums or dialkylaluminum halides in methyl chloride solvent in the temperature range —30° to —100°C., immediate polymerization commences (2, 3, 4, 5, 6). 

Figure 11. Catalytic activity of 0.9 Al/Ti separated solids and their combinations with dialkylaluminum halides. I. i-Bu Al-TiCh solid O without activation activated with i-Bu2AlCl ...

Figure 12. Catalytic activity of 0.9 i-BusAl-TiCh separated solid activated with dialkylaluminum halides.. modified with i-Bu2AlCl O, modified with EtoAlCl polymerization time—22 hours.

Dialkylaluminum hydrides, important reagents industrially, are prepared by treatment" of dialkylaluminum halides with LiH, e.g., diisobutylaluminum hydride (or deuteride) may be prepared by treatment of (i-C4H,)jAlCl with LiH in ether LiH or LiD in ether is cooled to 0°C and (i-C,H,)jAlCl is added dropwise under N so that an xs of LiH exists. The mixture is heated to reflux for 48 h or until a Cl test shows negative. After workup (i-C,H,)2AlH is obtained in 67% yield. 

Type (a) behavior is shown by many first generation catalyst systems, e.g., a-TiCla, VCI3, etc., when used with dialkylaluminum halides as co-... 

In sum, dialkylaluminum halides are more reactive than trialkyl-aluminums. The effect of temperature is different for each initiator system and overall conversions are affected by the extents of both initiation and termination. 

Dialkylaluminum halides, RjAlX, X = Cl, Br, I, are prepared in the same way (neglecting association). For X = Cl slight xs of AICI3 is used, and the small amount of RAICI2 thus formed is trapped by adding NaCl as NaRAlCls ... 

Dialkylaluminum halides, alkoxides, phenoxides and thiolates react with ethylene only in the presence of R3AI (via alkyl group exchange and growth of the trialkylaluminum) ". The strong association in R2AINR2 prevents reaction with ethylene even in the presence " of R3AI. 

Trimethylaluminum (strongly associated) and dialkylaluminum halides do not react with HC=CH under these conditions. 

The alkinyl group bridges strongly ". Consequently, RjAlCSCR are dimeric and stable. Although the alumination of alkynes (see 5.3.3.5.2) or the reaction between dialkylaluminum halides and metallated alkynes is the preferred method of preparation, disproportionation of R3AI with (R C=C)3A1 in ether can also be used. ... 

Dialkylaluminum halides react with diazomethane at low temperatures, yielding nitrogen and very unstable dialkyl(halomethyl)aluminums.237... 

This hypothesis is made quite probable by the isolation of the complex between gallium chloride and diethylaluminum chloride. Moreover, inclusion of potassium chloride in the reaction mixture to complex with the dialkylaluminum halide and free the gallium chloride raises the yield to 90% of triethylgallium (142). 

The mechanism of polymerization-initiation with dialkylaluminum halides in conjunction with Bronsted acids may be visualized as follows First the Bronsted acid and the AIR2X interact to provide the true initiating species, H A1R2X2 ... 

CHART 3 Dialkylaluminum halide/hydride based initiator systems. 

SCHEME 7 Initiation by charge transfer complexes derived from dialkylaluminum halides in conjimction with electron acceptors. 

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