Acids Alkylaluminum halides

Aluminum(III) complexes are amongst the most common Lewis acids. In particular, aluminum halide species (e.g., A1C13, AlBr3) are commercially available and are widely used for various reactions. Other types of Lewis acid such as aluminum alkoxides, alkylaluminum halides, and trialkylaluminum species are also used for many kinds of Lewis-acid-mediated reactions. 

AICI3 is a moisture-sensitive and strong Lewis acid. It is a first choice for Friedel-Crafts-type reactions, which provide numerous important transformations in laboratory and industry. It can also be applied to the transformation of alkenes to ketones via alkylaluminum halides.303 Hydrozirconation of an olefin and subsequent transmetalation from zirconium to aluminum gives the corresponding alkylaluminum dichloride, and the subsequent acetylation by acetyl chloride affords the corresponding ketone in high yield (Scheme 66). 

B,) Treatment of an organo- or a hydrido-nickel(II) compound with a Lewis acid. Organometallic compounds, such as alkylaluminum halides, which have Lewis acid properties, can also be used. 

Not only phosphines or phosphites but also phosphoric acid trisdialkyl-amides (40), sulfoxides (41), etc. have been used as electron donors in the preparation of the catalyst. In addition, the catalytic activity of tetra-methylcyclobutadienenickel dichloride and alkylaluminum halides has been studied in detail (42, 43). 

The primary (7, 47) and most commonly used organonickel compounds have been the dimeric 7r-allyl- (or substituted Tr-allyl-) nickel halides (1) (Scheme 1) or their monophosphine adducts (2) in the presence of Lewis acids such as aluminum halides or alkylaluminum halides (4, 48-53). The... 

There can be little doubt that the active species involved in most or even all of the various combinations described in Section II is HNi(L)Y (see below), because the different catalysts prepared by activating the nickel with Lewis acids have been shown to produce, under comparable conditions, dimers and codimers which have not only identical structures but identical compositions. On modification of these catalysts by phosphines, the composition of dimers and codimers changes in a characteristic manner independent of both the method of preparation and the nickel compound (2, 4, 7, 16, 17, 26, 29, 42, 47, 76). Similar catalysts are formed when organometallic or zero-valent nickel complexes are activated with strong Lewis acids other than aluminum halides or alkylaluminum halides, e.g., BFS. 

Less clear is the sequence which leads to the formation of the active species in the case of catalysts prepared from zero-valent nickel complexes and aluminum halides or alkylaluminum halides (method C2). The catalytic properties of these systems, however—in particular, the influence of phosphines (76)—leaves no doubt that the active species is also of the HNiY type discussed above. In this connection, a recent electron spin resonance report that nickel(I) species are formed in the reaction of COD2Ni with AlBr3 (83 ), and the disproportionation of Ni(I) to Ni(II) and Ni(0) in the presence of Lewis acids (69) should be mentioned. 

VDC polymer degradation and, 25 717 2-Alkyl-alcohols. See Guerbet alcohols Alkylalkanolamines, 2 140 Alkylaluminum compounds, 2 285 Alkylaluminum halides, 2 358 Alkylaluminum reagents, in triorganotin preparation, 24 815-816 Alkyl amino acids, protonated, 17 780 Alkylaminomethanols, 12 112 AT-Alkyl amino propionates, 24 148... 

General considerations, 281 Intramolecular Alkylaluminum halides, 5 Dicarbonylcyclopentadienylcobalt, 96 Meldrum s acid, 172 Specific reactions 2-Acetoxy-l, 3-butadiene, 71... 

Upon completion of the reaction the reaction mixture was treated with a diluent which is a nonsolvent for PVC. Suitable diluents included aliphatic or aromatic hydrocarbons such as hexane, heptane, or benzene or compounds containing an active hydrogen atom such as acetic acid or a lower alkanol such as methanol or ethanol. Methanol was the preferred diluent by virtue of its miscibility with the preferred reaction medium (chlorobenzene), its ability to react readily with and deactivate an aluminum alkyl or alkylaluminum halide, and its low boiling point and water solubility. 

CLAISEN REARRANGEMENT Alkylaluminum halides. Lithium diisopropylamide. Potassium hydride. Sodium dithionite. Titanium(TV) chloride. Trifluoroacetic acid. Trimethylaluminum. 

Aryltetralin lignans. This ring system can be prepared in high yield by a Prins reaction of a 1,4-diaryl-1-butene with paraformaldehyde catalyzed by an alkylaluminum halide prepared from CHjAlCh and (CH,) A1C1 (1 1), which is more acidic than (CHO AICI alone. 

Excess nucleophile is often needed in polymerization of more nucleophilic monomers. For example, esters, ethers, and amines afe used in large excess over aluminum halides and alkylaluminum halides to control polymerization of vinyl ethers [269]. The original Lewis acid is no longer available and covalent species are activated by the Lewis acid/nucleophile complex. Carbenium ions are additionally deactivated by excess nucleophile. 

Several of the trialkylaluminum and alkylaluminum halides and hydrides mentioned above are commercially available. Alkynyl, alkenyl, cyclopentadienyl, and aryl derivatives are, in general, not commercially available and must be synthesized for laboratory use. Alkynyl derivatives can be prepared by salt metathesis, as in the reaction of Et2AlCl with NaC=CEt to give Et2AlC=CEt. The acidity of terminal alkynes is sufficient for preparation of alkynyl aluminum compounds by alkane or hydrogen elimination upon reaction with a trialkylaluminum or an aluminum hydride (equation 17), respectively. TriaUcynyl aluminum compounds are typically isolated as Lewis base adducts to stabilize them against otherwise facile polymerization. Alkenyl compounds of aluminnm have similarly been prepared. 

Alkyl derivatives of metals such as aluminum, boron and zinc are fairly active Friedel-Crafts catalysts. However, hyperconjugative effects result in a lowering of the electron deficiency. In the case of metal alkoxides this effect is even stronger, and, as a result, they are fairly weak Lewis acids. Metal alkyls, such as alkylaluminums, alkylaluminum halides and sesquihalides are also vital components of Ziegler-Natta catalyst systems which sometimes are utilized for Friedel-Crafts-type reactions. For example, alkylations of aromatics with alkenes in the presence of a Ziegler-Natta catalyst such as AIR3 -1- TiCU results in lower-chain alkylates. Even alkylaluminum halides and sesquihalides serve as Friedel-Crafts catalysts. 

The autocatalytic formation of alkanes, alkenes, poljfmers, AIX3 and HX prevents the use of higher alkyl chlorides or bromides for the synthesis of the corresponding sesquihalides in nonethereal solvents The electron-pair acceptor acid-catalyzed elimination of HX (X=C1, Br) cannot occur with CH3X and is unimportant for CjHjX provided T is as low as possible. To circumvent these problems, alkylaluminum sesquiiodides (weaker electron-pair acceptor acids) are used to initiate the reaction and EtjO is added to form adducts with the alkylaluminum halides ... 

Several important homogeneous catalytic reactions (e.g. hydroformylations) have been accomplished in water by use of water-soluble catalysts in some instances water can act as a solvent and as a reactant for hydroformylation. In addition, formation of aluminoxanes by partial hydrolysis of alkylaluminum halides results in very high activity bimetallic Al/Ti or Al/Zr metallocene catalysts for ethene polymerization which would be otherwise inactive. Polymerization of aryl diiodides and acetylene gas has recently been achieved in water with palladium catalysts. Finally, nickel-containing enzymes, such as carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase, operate in water with reaction mechanisms comparable with those of the WGSR or of the Monsanto methanol-to-acetic-acid process. ... 

The alkylaluminum halide-induced Friedel-Crafts acylation is a very general and synthetically useful reaction that allows the functionalization of unsaturated fatty compounds. Acylations were carried out with different acylating agents such as acyl chlorides, dicarboxylic acid dichlorides, cyclic anhydrides, unsaturated acyl chlorides, and aromatic and heteroaromatic carboxylic acid chlorides, yielding a large... 

Other examples are alkylation of the chain end in alkylaluminum halide coinitiated isobutylene polymerization (143). This type of counteranion exchange can also result in the formation of a Lewis acid that is too weak to ionize the chain end, as depicted in equation 15. 

ABSTRACT. Aldehydes, ketones and a,p-unsaturated aldehydes and ketones undergo a wide variety of reactions with unactivated alkenes in the presence of alkylaluminum halide catalysts. Ene reactions, Diels-Alder reactions, Prins reactions and cation-olefin addition reactions occur depending on the choice of substrate and Lewis acid. 

Addition of an electrophilic carbon species to alkenes is not difficult. The problem is controlling the reactions of the intermediate carbocation which is formed. Our initial approach to this problem was to explore Lewis acid catalyzed ene reactions as a means of controlling the reaction between a weakly nucleophilic alkene and a weakly electrophilic carbon-containing enophile.i During the course of these studies we have found that alkylaluminum halides have several unique properties which make them valuable catalysts for ene reactions and that by proper choice of reaction conditions, other classes of reactions can be induced to occur in synthetically useful yield. 2... 

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