Aluminum trihalides

The aluminum trihalides are particularly important Lewis acids in the chemical industry. They promote or catalyze a large variety of reactions. One of the most important applications is the Friedel-Crafts reaction, in which two molecules combine, forming a new C—C bond. For example, aluminum chloride or some other Lewis acid catalyzes the reaction between an acid chloride and benzene to form acetophenone ... 

Scheme 15. Reaction of 1 with aluminum trihalides A1X3(X = Cl, Br).

Photocycloadditions of naphthalene derivatives to alkcnes have been recently reviewed.60 Examples of such reactions are the photocycloaddition of naphthalene to 2,3-dihy-drofuran,61 of 4-methoxy-l-naphthonitrile to acrylonitrile62 and of 2-trimethylsiloxynaph-thalene to methyl acrylate.63 2-Naphthols undergo cycloaddition with ethene in the presence of aluminum trihalides only.64 Other bicyclic aromatic compounds, e.g. A-acylindoles65-67 and /V-methylphenanthrene-9,10-dicarboximide,68 have also been studied in detail. Irradiation of 5/f-dibenzo[u,i7]cyclohepten-5-one (21) and dimethyl 2-methylfumarate (22) in dioxane gives the cyclobutane adduct 23 in 73% yield.69... 

The formation of molecular complexes between aluminum trihalides and pyridine or alkylpyridines has been the subject of systematic studies.35,36 Calorimetric data yield bond dissociation energies D(X3Al—py) of 323, 308 and 264 kJ mol-1 for X = C1, Br and I, respectively, and this same order is found for alkylpyridine adducts, although the A1—N bond is weakened in the case of lutidine by the effects of steric hindrance. For gallium halides the values of D(X3M—py) are smaller 248, 237 and 195 kJ mol-1 for chloride, bromide and iodide adducts, respectively. 

These compounds are easily hydrolyzed and decompose at temperatures above — 15°. They are soluble in polar solvents. Reactions between bis[trifluoromethyl] tellurium dichloride or dibromide with boron trihalides or aluminum trihalides resulted in decomposition1. 

In contrast to the aluminum trihalides, which form A12X6 dimers and thereby complete the valence octet on Al, the boron trihalides are strictly monomeric, trigonal... 

AIF3 is made by reaction of AI2O3 with HF gas at 700 °C (equation 17), while the rest of the trihalides may be prepared by the direct combination of the elements, a highly exothermic process. Of the four aluminum trihalides, AIF3 is unique in being nonvolatile, insoluble, and in possessing a much higher heat of formation (Table 5). 

AIX3 (Aluminum trihalides, especially AICI3, AlBr3, their complexes with alkali metals, or onium halides). 

The widely applicable Fischer-Hafner method has been used to prepare arene complexes of most of the transition metals. The method involves the reaction of metal halide, aromatic hydrocarbon, aluminum trihalide, and aluminum metal, e.g. 53, 7576)(M = Cr, V),... 

Bisarene cations of Cr, Mo, and W are best synthesized by the reaction of aromatic hydrocarbon, metal halide, aluminum trihalide and aluminum metal at elevated temperature. Aromatic hydrocarbons, such as benzene, toluene, mesitylene, and hexamethylbenzene have been employed (Table III). The method is not applicable, however, when the aromatic hydrocarbon is itself reactive under Friedel-Crafts conditions. The bisarene cations are readily reduced to the neutral compounds by aqueous dithionite or, in the case of Mo and W, by alkaline disproportionation, e.g. 152),... 

Bisarene chromium compounds have been shown to undergo reversible exchange with aromatic hydrocarbons in the presence of aluminum trihalides (207). The exchange reaction has been used to improve the preparation of the bisbenzene chromium cation via the more readily prepared bismesitylene chromium cation 157b). 

The polynuclear cation [(CeHe)3Co3(CO)2] has been reported from the reaction of Hg[Co(CO)4]a or Coa(CO)0 with benzene in the presence of an aluminum trihalide (66, 114). The cation is believed to have the structure (XXXI) analogous to (7r-C5H5)3Ni3(CO)a (289). Neutral polynuclear complexes of the type (arene)Co4(CO)g (arene = benzene, toluene, anisole, />-xylene, mesitylene, tetrahydronaphthalene) have been prepared by the reaction of (RC=CH)Co2(CO)e (R = H or Ph) with norbornadiene in the appropriate aromatic solvent or in some cases by simply warming Co4(CO)i2 with the arene (247, 365). The compounds are believed to have the structure (XXXII) derived from that of Co4(CO)i2 (435) by replacement of three apical CO groups by the arene. A normal coordinate analysis has been carried out on several of... 

The Fries rearrangement proceeds via ionic intermediates but the exact mechanistic pathway (whether it is inter- or intramolecular) is still under debate. There are many reports in the literature that present evidence to support either of the pathways, but it appears that the exact route depends on the structure of the substrates and the reaction conditions. The scheme depicts the formation of an ortho-acylated phenol from a substituted phenolic ester in the presence of aluminum trihalide catalyst. The photo-Fries rearrangement proceeds via radical intermediates. ... 

The reaction of organometallics with aluminum trihalides in a 2 1 stoichiometry leads to R AIX. A 1 1 stoichiometry gives M[RA1X3] rather than RAlXj. Adducts are obtained in the presence of ether. Complex formation is reversible only for weak bases such as phenyl ethers. Otherwise, ether cleavage may occur when the etherates are heated at > 100°C. However, with bulky organo groups the ether may be removed in vacuo ... 

Due to their close relationship with carbonic acid halides, cyanuric halides can undergo Friedel-Crafts-type reactions which lead to the formation of C-C bonds between the triazine ring and an aromatic compound. By analogy, the conversion is catalysed by Friedel-Crafts catalysts such as aluminum trihalides, heavy-metal salts, and protonic acids. Generally, the hydrogen halide formed is evaporated or trapped by a base96,91,113-124... 

The liquid clathrate phase will dissolve substances that act as olefin hydrogenation catalysts, creating homogeneous hydrogenation catalysts.Polymerization catalysts comprised of stable liquid clathrate aluminoxane, aromatic solvents, and organic, inorganic, or organometallic compounds were described.Liquid clathrate compositions comprised of a metal halide, a quaternary ammonium salt, a quaternary phosphonium salt, or a ternary sulfonium salt an aluminum trihalide and an aromatic hydrocarbon have proven useful as reusable aluminum catalysts in Friedel-Crafts reactions. 

The first instance of an aluminum trihalide adduct with an Af-heterocyclic carbene was reported in 2004 (phosphanylsilylcarbene adducts had previously been reported [128]). The adduct and its gallium analog were prepared from the reaction of ImMe4 with aluminum trichloride or gallium trichloride in toluene the aluminum complex was crystallographically characterized [129]. Later, NHC adducts of AII3 were also structurally characterized [130]. 

An alkyl group can replace a hydrogen atom of benzene in the Friedel-Crafis alkylation reaction. This reaction requires an alkyl halide, with an aluminum trihalide as the catalyst. The catalyst produces an electrophilic species, which may be a carbocation or a carbocation complexed with a counter ion. For simplicity in writing equations, we will show only the free carbocation. The reaction is commonly carried out only with alkyl bromides or alkyl chlorides. Aryl hahdes and vinyl halides do not react because the carbocations derived from these compounds do not form under usual reaction conditions. In contrast, tertiary carbocations, such as the ferr-butyl carbocation, readily form. 

AICI3], constitutes the only structurally characterized complex containing a dative Sn-Al bond [105]. In addition, the synthesis of Cp2Sn-AlX3 (X = Cl, Br) was reported [106]. In these complexes, the Sn(II) atom coordinates through its electron lone pair to the Lewis acidic aluminum trihalides. 

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