Sesquihalides

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

An obvious method to investigate the formation and the nature of the catalytically active nickel species is to study the nature of products formed in the reaction of complexes such as 3 or 4 with substrate olefins. This has been investigated in some detail in the case of the catalytic dimerization of cyclooctene to 1-cyclooctylcyclooctene (17) and dicy-clooctylidene (18) [Eq. (4)] using as catalyst 7r-allylnickel acetylacetonate (11) or 7r-allylnickel bromide (1) activated by ethylaluminum sesquihalide or aluminum bromide (4). In a typical experiment, 11 in chlorobenzene was activated with excess ethylaluminum sesquichloride cyclooctene was then added at 0°C and the catalytic reaction followed by removing... 

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 %. 

The most widely used preparative method of allylindium(m) or propargylindium(lll) compounds is the oxidative addition of metallic indium or indium(l) halides to allylic or propargyl substrates.4 26 27 Allylic bromides and iodides serve as good allylic sources without any other activation. In the case of allylic chlorides, a proper additive such as lithium iodide is required to promote the oxidative addition. Allylic indium compounds prepared by oxidative addition of metallic indium are considered to exist as the sesquihalide structure (allyl jImXj), which has been... 

Allylindium sesquihalides react with terminal epoxides to afford the corresponding bishomoallyl... 

Triorganogallium and -indium reagents react with a,/3-unsaturated nitrile, ketone, and ester to give 1,4-addition products regioselectively (Table 31). In contrast, the reaction of allylgallium and allylindium sesquihalides with a,/3-unsaturated carbonyl compounds proceed in a 1,2-addition mode, whereas 1,4-addition takes place with a,/3-unsaturated nitriles.294... 

No reaction occurs when triethylaluminum, aluminum chloride, stannic chloride, titanium tetrachloride, diethylzinc or triethylboron are used in lieu of an organoaluminum halide or sesquihalide. 

Since the styrene-methyl acrylate and styrene-methyl methacrylate copolymers could be prepared in toluene solution at 25°C., it became possible to investigate the influence of free radicals on the ethylaluminum sesquihalide complexed system. 2-Methylpentanoyl peroxide (Lucidol R-226), having a half-life of 10 hours at 27 °C. in 0.2M solution in mineral spirits was used as the free radical source at 25 °C. 

A classic synthetic route to alkylaluminum halides is reaction of aluminum metal with alkyl halides. This procedure affords alkylaluminum sesquihalides, equimolar mixtures of dialkylalu-minum halides and alkylaluminum dihalides (Equation (5)). 

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. 

CgHsBr 4- B— [CgHsBBr]CeHsBBrj CeHsBr -t- A1—> —>(C6Hs)3Al2Br3 For Al, the sesquihalide is the final product. ... 

Both Al and In slurries react with aryl halides . For Al, the sesquihalides are formed ... 

Aluminum sesquihalides " or even mixtures of metallic Al, alkyl halide and trialkoxy-borane, can also be used. Trialkoxyboroxines, from trialkoxyboranes and boron trioxide, are convenient boron substrates ... 

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 ... 

The RAlXj, R2AIX or sesquihalides (RXAIX2AIR2) are available by the reaction of metallic Al with organic halides (RX) (see 5.3.3.2.2.) Redistributions of these compounds, similar to Eqs. (a) and (b), take place smoothly between the sesquihalides and AIX3 to give RAIX2 ... 

The dehalogenation of organoaiuminum halides with active metals, such as Na, K is is still of importance considering the easy access to the organoaiuminum sesquihalides (see 5.3.3.2.2)i =. 

Modifications are possible -. Thus ethylaluminum sesquichloride can be converted quantitatively to Et2AlCl. Another advantage is the precipitation of finely divided and active Al metaU. This can again be utilized in the preparation of aluminum sesquihalides. 

The action of alkyl halides with In metal is slow and R3ln2X3 sesquihalides are... 

Propargyl alcohols add to allylic indium sesquihalides, but the mechanism of the process is not known. Molybdenum complexes have been used to cyclize enynes and dienynes . ... 

Organoaluminum sonochemistry is not yet well developed despite the synthetic and economic interest. Aluminum, a ductile metal, is easily activated by sonication, as evidenced by the use of foils to determine the energy of cleaning baths. Alkyl halides react with aluminum at room temperature in THF to give the sesquihalide, reduced to the trialkyl compound in the presence of magnesium. Examples are known with bromomethane or -ethane.1 2,183 reaction occurs with stirring under similar conditions. Triethylaluminum was used in sonochemical transmetallation reactions leading to zinc and boron alkyls (Eq. 38). 

While organoboron halides R BX and RBX are monomeric, like R B or BXj, the derivatives of Al, Ga and In associate through halogen bridges. Direct reaction between aluminium and methyl or ethyl halides gives the sesquihalides. 

The metal generally needs to be activated either with some preformed aluminium alkyl or with iodine or AICI3. Propyl and higher alkyl halides, however, give mainly AICI3 and hydrocarbons on reaction with aluminium. The sesquihalides disproportionate... 

A particularly active area of halide chemistry has been the investigation of the reduced halide systems. Dihalides of Sm, Eu and Yb have been known for years, but thorough examination of their properties has only recently been undertaken. Some of the most interesting reduced halides have been observed in the metal-rich chloride, bromide and iodide systems of normally trivalent rare earths. Numerous intermediate phases, RX ,(2solid state. The gaseous dihalides... 

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