Diethylaluminum chloride, catalyst

Ziegler, Gellert, Holzkamp, Wilke, Duck and Kroll (72) have shown that the hydride transfer reaction of alkylaluminum occurs much more easily with trialkylaluminum than with the more electrophilic diethylaluminum chloride. Catalysts must be more anionic in order to produce oligomers which involve large amounts of hydride transfer than with polymerization catalysts where hydride chain transfer must be minimized. Thus the oligomerization catalyst employed by Bestian and Clauss was more anionic, or less cationic, than the usual polymerization catalyst where anionic chain transfer is minimized. 

The titanium trichloride-diethylaluminum chloride catalyst converted butadiene to the cis-, trans,-trans-cyclododecatriene. Professor Wilke and co-workers found that the particular structure is influenced by coordination during cyclization between the transition metal and the growing diene molecules. Analysis of the influence of the ionicity of the catalyst shows effects on the oxidation and reduction of the alkyls and on the steric control in the polymerization. The lower valence of titanium is oxidized by one butadiene molecule to produce only a cis-butadienyl-titanium. Then the cationic chain propagation adds two trans-butadienyl units until the stereochemistry of the cis, trans, trans structure facilitates coupling on the dialkyl of the titanium and regeneration of the reduced state of titanium (Equation 14). 

Twelve-membered rings have been obtained using coordination catalysts. The trans,trans,cis-cyclododecatriene has been prepared with a tetrabutyl titanate—diethylaluminum chloride catalyst (48,49) and with a chromium-based system (50). The trans,trans,trans- somer has been prepared with a nickel system. 

Erom 1955—1975, the Ziegler-Natta catalyst (91), which is titanium trichloride used in combination with diethylaluminum chloride, was the catalyst system for propylene polymerization. However, its low activity, which is less than 1000 g polymer/g catalyst in most cases, and low selectivity (ca 90% to isotactic polymer) required polypropylene manufacturers to purify the reactor product by washing out spent catalyst residues and removing unwanted atactic polymer by solvent extraction. These operations added significantly to the cost of pre-1980 polypropylene. 

The eailiest Ziegler-Natta catalysts were combinations of titanium tetrachloride (TiCl4) and diethylaluminum chloride [(CH3CH2)2A1C1], but these have given way to more effective zirconium-based metallocenes, the simplest of which is bis(cyclopentadi-enyl)ziiconium dichloride (Section 14.14). 

The experimental isotope effects have been measured for the reaction of 2-methylbutene with formaldehyde with diethylaluminum chloride as the catalyst,27 and are consistent with a stepwise mechanism or a concerted mechanism with a large degree of bond formation at the TS. B3LYP/6-31G computations using H+ as the Lewis acid favored a stepwise mechanism. 

Materials. 5-Methyl-1,4-hexadiene was obtained by the codimerization of isoprene and ethylene with a catalyst (18) consisting of iron octanoate, triethylaluminum and 2,2 -bi-pyridyl. The product mixture which contained principally 5-methyl-1,4-hexadiene and 4-methy1-1,4-hexadiene was fractionated through a Podbielniack column to yield high purity (>99%) 5-methylxhexadiene, b.p. 92.80C,njj 1.4250 (Lit. (19) b.p. 88-89°C, np 1.4249). 1-Hexene (99.9% purity), 1-decene (99.6% purity), 4-methyl-1-hexene (99.5% purity) and 5-methyl-l-hexene (99.7% purity) were obtained from Chemical Samples Co. 6-TiCl3 AA (Stauffer Chemical Co.j contains 0.33 mole AICI3 per mole of TiClj). Diethylaluminum Chloride was obtained from Texas Alkyls (1.5 M in hexane). 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

The Lewis acid catalyzed reaction of furan (169) with ketovinylphosphonate 170 produced a mixture of adducts, both of which slowly underwent retro Diels-Alder reactions at room temperature121. When diethylaluminum chloride was used as the catalyst, the endo selectivity (with respect to the keto functionality) was enhanced from 171/172 = 58/42 to 78/22 by raising the reaction temperature from — 25 °C to 0°C (equation 47). This is in agreement with the FMO theory, since initial Lewis acid complexation is with the phosphonate group. 

Sudo and Saigo153 reported the application of ds-2-amino-3,3-dimethyl-l-indanol derived l,3-oxazolidin-2-one 231 as a chiral auxiliary in asymmetric Diels-Alder reactions. The TV-crotonyl and TV-acryloyl derivatives were reacted with cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethyl-l,3-butadiene, using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded the expected cycloadducts in moderate to high yields (33-97%) with high endo selectivities and high de values (92% to >98%). 

Carbohydrates have found widespread use as chiral auxiliaries in asymmetric Diels-Al-der reactions156. A recent example is a study conducted by Ferreira and colleagues157 who used carbohydrate based chiral auxiliaries in the Lewis acid catalyzed Diels-Alder reactions of their acrylate esters 235 with cyclopentadiene (equation 66). Some representative results of their findings, including the ratios of products 236 and 237, have been summarized in Table 9. The formation of 236 as the main product when diethylaluminum chloride was used in dichloromethane (entry 3) was considered to be the result of an equilibrium between a bidentate and monodentate catalyst-dienophile complex. The bidentate complex would, upon attack by the diene, lead to 236, whereas the monodentate complex would afford 236 and 237 in approximately equal amounts. The reversal of selectivity on changing the solvent from dichloromethane to toluene (entry 2 vs 3) remained unexplained by the authors. 

Cadogan and coworkers160 developed a fructose-derived l,3-oxazin-2-one chiral auxiliary which they applied in the Diels-Alder reactions of its iV-enoyl derivatives 246 with cyclopentadiene using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded mixtures of endo 247 and exo 248 (equation 68). The catalyst binds to the chiral dienophile in a bidentate fashion (co-ordination to both carbonyl groups). As a consequence, the dienophile is constrained to a rigid conformation which accounts for the almost complete diastereofacial selectivities observed. 

Taguchi and coworkers175 studied the Lewis acid catalyzed asymmetric Diels-Alder reactions of chiral 2-fluoroacrylic acid derivatives with isoprene and cyclopentadiene. When a chiral l,3-oxazolidin-2-one and diethylaluminum chloride were used as the chiral auxiliary and the Lewis acid catalyst, respectively, a de of 90% was observed for the reaction with isoprene. The reaction with cyclopentadiene afforded a 1 1 mixture of endo and exo isomers with de values of 95% and 96%, respectively. The endo/exo selectivity was improved by using 8-phenylmenthol as the chiral auxiliary. Thus, the reaction... 

Mayoral and colleagues210 studied the same reaction catalyzed by a menthoxyaluminum catalyst supported on silica gel and alumina. The catalyst was prepared by treatment of the solid support with diethylaluminum chloride and (—)-menthol. The silica-supported catalyst proved more active than the alumina-supported catalyst. The reaction rates and enantioselectivities depended strongly on the amount of (—)-menthol used. The highest ee obtained was 31% at 81% conversion (endo/exo = 10/90). 

Lewis acids such as zinc chloride, boron trifluoride, aluminum chloride, and diethylaluminum chloride catalyze Diels-Alder reactions.8 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the cycloaddition is still believed to be concerted, and high stereoselectivity is observed.9 10 Lewis acid catalysts also usually increase the regioselectivity of the reaction. 

The diethylaluminum chloride was also a catalyst for the polymerization of ethylene. Very similar products were obtained in parallel polymerizations carried out at 300° with diethylaluminum chloride and with a mixture of aluminum chloride and aluminum. The distillation curves showed marked plateaus for C6, Cs, and Cj0 hydrocarbons with complete absence of C5, C7 and C9. The bromine numbers indicated that these fractions were mixtures of paraffins and olefins. 

The actual polymerization takes place in an autoclave under inert atmosphere, where the supernatant liquid of the foregoing step is placed with the dried and rectified monomer and the second catalyst compound, namely diethylaluminum chloride in 1,2-dichloroethane solution (15). The polymerization is conducted at 70°C for 60 min while stirring well. According to this recipe, a series of cyclic monomers can be polymerized. Examples are shown in Table 1.3. 

Examples of a-olefins include 1-pentene, 1-hexene, 1-octene, etc. A suitable catalyst is titanium trichloride with diethylaluminum chloride as co-catalyst. Hydrogen is a chain transfer agent. 

Hie study of effects of the catalyst components also help clarify the ionic factors in the steric control of isotactic polyvinylethers. Dall Asta and Bassi (15) studied the polymerization of butylvinylether with various alkylaluminum halides. They found that diethylaluminum chloride and ethylaluminum dichloride were the most effective catalysts for the production of isotactic polymer. Ethylaluminum dibromide and ethoxyaluminum dichloride were of questionable effectiveness, while diethylaluminum fluoride was completely ineffective. 

In their review, Natta and co-workers (6) were able to show that the highest content of crystalline polyvinylisobutylether was obtained with diethylaluminum chloride and ethylaluminum dichloride, and lesser amounts with aluminum bromide. Triethylaluminum was ineffective as a catalyst. 

Other effects of the ionicity of the catalyst on its activity has been studied by Natta, PaSQUON, Zambelli and Gatti (66). The polymerization of propylene was carried out with alpha titanium trichloride and diethylberylium or triethylaluminum. They found that catalysts from the alkylberylium were more stereospecific than those from alkyl aluminum. On the other hand their study of titanium trichloride with diethylaluminum iodide, diethylaluminum bromide, diethylaluminum chloride or triethylaluminum showed that the greater stereospecificity was produced by the iodide containing catalyst. The less electrophilic catalyst produced greater crystallinity than the corresponding bromide or chloride component. 

Diels-Alder catalysts Alkylaluminum halides, 5, 173 Boron trifluoride etherate, 43 Diethylaluminum chloride, 173 Dimethylaluminum chloride, 5 Sodium dodecyl sulfate, 281 Titanium(IV) chloride-Diethylaluminum chloride, 309... 

Alkylaluminum halides have been investigated as catalysts in the benzalaniline-diazomethane addition.342 Reaction occurs at — 78°C in the presence of diethylaluminum chloride to yield the triazoline adduct diethyl-aluminum iodide, however, leads only to an aziridine. 

The complex RhCl(ttp), where ttp = PhP(CH2CH2CH2-PPh2)2, in the presence of either triethylaluminum or diethylaluminum chloride, is an effective homogeneous catalyst for hydrogenation of 1-olefins and 1-octyne. The rates of hydrogenation of substituted olefins are considerably slower than for terminal olefins. H-l and P-31 NMR spectra were used to identify several different chemical species [including RhH(ttp)] in these catalyti-cally active solutions. The observed rate of hydrogenation of 1-octene to n-octane at 20 0.3°C and under a constant H2 pressure of 750 torr is 6.4 x min 9... 

Grafting by in situ Polymerization of Butadiene. The polymerization of butadiene to a high cw-1,4-polybutadiene with a catalyst system containing diethylaluminum chloride and a cobalt compound is now a well established technique (1, 9,15,18, 22). This catalyst system is particularly effective when the cobalt compound is soluble in the reaction medium. 

Cleavage of epoxides andoxetanes.5 In the presence of diethylaluminum chloride as catalyst, cyanotrimethylsilane reacts with epoxides and oxetanes regioselectively to give open-chain products in which the CN group is attached to the less substituted a-carbon of the cyclic ether. 

Debenzoylation of the ribose moiety in each of these compounds was also reported. The use of diethylaluminum chloride as a catalyst in the glycosylation of 293 by 294 led to the exclusive formation of /V-glycosylated thiophene 300. Heating 300 with methanolic ammonia at 75°C afforded 1-/3-D-ribofuranosylthieno[3,4-d]pyrimidin-4(l//)-one 301 as the main product (88TL3537 90MI7). 

The Ziegler-Natta catalyst used for the reaction consisted of 1.0% neodymium versatate dissolved in cyclohexane solution, IM of diethylaluminum chloride... 

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