Alkyl aluminum compounds

Organochromium Catalysts. Several commercially important catalysts utilize organ ochromium compounds. Some of them are prepared by supporting bis(triphenylsilyl)chromate on siUca or siUca-alumina in a hydrocarbon slurry followed by a treatment with alkyl aluminum compounds (41). Other catalysts are based on bis(cyclopentadienyl)chromium deposited on siUca (42). The reactions between the hydroxyl groups in siUca and the chromium compounds leave various chromium species chemically linked to the siUca surface. The productivity of supported organochromium catalysts is also high, around 8—10 kg PE/g catalyst (800—1000 kg PE/g Cr). 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

Al Ti in the range of 0.9—1.0 appeared optimum for i7j -l,4-polyisoprene yield (20). Other factors such as catalyst preparation temperature, influence of the R group in the alkyl aluminum compound (R Al), and catalyst aging have been extensively studied (16,17). Another variable studied was the effect of... 

Nickel(O) reacts with the olefin to form a nickel(0)-olefin complex, which can also coordinate the alkyl aluminum compound via a multicenter bond between the nickel, the aluminum and the a carbon atom of the trialkylaluminum. In a concerted reaction the aluminum and the hydride are transferred to the olefin. In this mechanistic hypothesis the nickel thus mostly serves as a template to bring the olefin and the aluminum compound into close proximity. No free Al-H or Ni-H species is ever formed in the course of the reaction. The adduct of an amine-stabihzed dimethylaluminum hydride and (cyclododecatriene)nickel, whose structure was determined by X-ray crystallography, was considered to serve as a model for this type of mechanism since it shows the hydride bridging the aluminum and alkene-coordinated nickel center [31]. 

Natta A process for polymerizing propylene and other higher olefins, catalyzed by crystalline titanium trichloride and an alkyl aluminum compound such as triethyl aluminum. The polymer can exhibit various types of stereoregularity, depending on the catalyst and the conditions. Invented in 1954 by G. Natta at the Istituto de Chimica Industrial del Politecnico di Milano, Italy, and commercialized in 1957. Now used widely, worldwide. See also Ziegler, Ziegler-Natta. 

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

Another interpretation that may be taken into consideration, kinetically equivalent to the former one, is a total substitution of the polymeric alkyl-aluminum compound which is bound to a catalytically active complex containing the transition metal, as follows ... 

C.S.Marvel et al, JACS 7% 5408-9( 1950) Alkyl-Aluminum Compounds. See Aluminum Alkyls... 

Telraorganotins, RaSn, prepared either by alkylation of tin halides with Grignard Reagents or alkyl lithium by reaction of an organic halide with a tin-sodium alloy by direct reaction of tin with an organic halide or by reaction of stannic chloride with alkyl aluminum compounds. 

Terpolymers of CO, C2H4 and propylene have been prepared using Ziegler-Natta type catalysts consisting of a combination of alkyl aluminum compounds and vanadium oxyalkoxides47>. The same procedure was also used to incorporate methyl vinyl ketone as the fourth component in the polymers. 

When dienones such as 55 are subjected to the epoxidation conditions the electron-poorer C=C double bond is selectively epoxidized. The other C=C bond can be functionalized further, for example, it can be dihydroxylated, as shown in the synthesis of the lactone 56 (Scheme 10.11) [82]. Stannyl epoxides such as 57 (Scheme 10.11, see also Table 10.8, R1 = n-Bu3Sn) can be coupled with several electrophiles [72], reduction of chalcone epoxide 58 and ring opening with alkyl aluminum compounds provides access to, e.g., the diol 59 and to phenylpropionic acids (for example 60). Tertiary epoxy alcohols such as 61 can be obtained with excellent diastereoselectivity by addition of Grignard reagents to epoxy ketones [88, 89]. 

These observations are for the pure compounds, but the association of alkyl aluminum compounds also occurs in solution. As described earlier in connection with the association of Grignard reagents, the association metal alkyls often gives different types of aggregates depending on the nature of the solvent. 

The filtrate obtained after collecting the crude product contains highly reactive alkyl aluminum compounds, and contact with water should be avoided. The alkyl aluminum compounds may be decomposed by the dropwise addition of 200 ml. of ethanol to the cooled solution followed by the cautious addition of water. 

Elastomeric copolymers are made by either solution or suspension process using a vanadium based catalyst along with alkyl aluminum compound as cocatalyst. In the suspension process propylene is used as a diluent, whereas in the solution process hexane is used as diluent. Superior catalysts based on supported titanium compounds have further improved the suspension process in recent years. In the conventional suspension process, ethylene, propylene and catalysts are fed continuously to a stirred reactor at 20 °C and 12 kg cm total pressure. Diethylzinc is used to control molecular weight. 

The combined use of a wide variety of tri alkyl aluminum compounds and alkylidene iodide serves as a highly convenient and versatile method for cyclopropanation of simple olefins under mild conditions. For example, treatment of 1-dodecene with CH2I2/R3AI (R = Me, Et, i-Bu) in dichloromethane at room temperature for 3-8 hr gave decylcyclopropane. in 96-98 6 yields. 

Alkyl aluminum compounds are known to be radical initiators. Kabalka and coworkers reported fhe first unequivocal example of a free-radical process in which the classical organoaluminum reagent PrsAl was used in fhe presence of O2 or under UV irradiation [203]. In modern studies, modified alkylaluminum reagents enabled more practical improvement in fhe control of diastereo- and enantioselectivity in radical initiation and reactions. 

Substituents in the alkyl chain of alkyl aluminum compounds, such as halogens, alkoxy, alkylmercapto, or dialkylamino groups, have varying effects on the stability of the aluminum alkyls to extents which depend on the position of the group in relation to the aluminum. Interaction between the substituents and aluminum leads to activation of both the A1—C and the C-substituent bonds. If, in the case of dialkyl halomethylalanes, the substituent (Cl, Br, or I) and the aluminum are linked to the same carbon atom, the compound is especially reactive. These compounds, since their etherates are stable, may be prepared readily in ethereal solution from dialkyl aluminum halides and diazomethane 97, 98) ... 

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