Triphenylaluminum

Organoaluminum compounds such as triphenylaluminum (527) are used for ketone synthesis[387]. On the other hand, the reaction of /-BuiAl affords the corresponding alcohol 528 by reductive carbonylation[388]. 

As observed with cyclohexanones, the diastereoselectivity of the addition reaction of trimeth-ylaluminum to 2-methylcyclopentanone depends on the stoichiometry of the reactants. Thus, addition of one equivalent of trimcthylaluminum proceeds via preferential tram attack whereas, due to the "compression effect , addition of an excess of the reagent leads to the formation of the equatorial alcohol via predominant attack from the cis side (Table 3)6. In contrast to the addition reactions with trimethylaluniinum, no reversal of the diastereoselectivity upon change of reagent stoichiometry was observed in the addition of triphenylaluminum to 2-methylcyclopentanone6. Even with an excess of the aluminum reagent trans attack predominates. However, the diastereoselectivity is lower than with the use of an equimolar amount of the reactants. 

Diphenylmercury, reaction with aluminum to give triphenylaluminum,... 

The flask is returned to the dry box, and the nearly dry solid that remains in it is transferred to an extraction thimble (123 mm. X 43 mm.) previously dried in a vacuum oven. The product is extracted in a dried Soxhlet apparatus (250 mm. x 50 mm.) with 250 ml. of dry ether (Note 5) in a carefully dried 300-ml. flask. The extraction is continued for 15-20 hours (Note 6), during which time white crystals of triphenylaluminum ctherate form in the flask. The flask and its contents are placed in a dry box, the ether is decanted, and the crystals are washed several times by decantation with small portions of dry ether. The tri-phenylalumimun etherate is dried at 25° under reduced pressure m.p. 126-130°. The ether of crystallization is removed by heating the etherate at 150° (0.1 mm.) for about 13 hours (Note 7). Pure triphenylaluminum, m.p. 229-232°, is obtained yield 23-27 g. (59-70%). 

Triphenylaluminum is useful as a component of catalyst systems for ionic or coordination polymerization of vinyl compounds. This preparation of the material in solid form enables the purity of the compound to be easily determined. The availability of solid triphenylaluminum permits the user a choice of solvents for a reaction, and a variety of concentrations of the reagent. Storage and dispensation of the reagent are more convenient in the solid form. 

Caution Triphenylaluminum and its etherate undergo decomposition in the presence of air and moisture. Upon contact with water, vigorous heat evolution and sparking have been observed. 

When aluminum Wool was substituted for strips of aluminum, foil, a 20% 5neld of triphenylaluminum was obtained. This yield... 

The reported addition of triphenylaluminum to diphenylacetylene to form 1, 2, 3-triphenylbenzaluminole 22) is another clear example of an acetylene insertion, this one being followed by a cyclization reaction. 

Fig. 16. NMR profiles in CD2CI2 at 25 °C of methyl methacrylate (MMA)-Lewis acid mixtures. Relationships between the chemical shift of the C=0 signal of MMA and the mole ratio of Lewis acid to MMA Lewis acids triphenylboron ( ), tris(pentafluorophenyl)boron ( ), tri-n-butylboron (A), triphenylaluminum (O), and methylaluminum bis(2,4,6-tri-tert-butylphenolate) ( )...

In the absence of an additive, tritylsodium polymerizes acenaphthylene (5). When the reaction is carried out in the presence of triphenylaluminum the reaction... 

Unsymmetric alkynylaluminum derivatives can be prepared by a) the reaction of sodium acetylides with dialkyl- or diaryluminum halides [92-94] (6) the reaction of terminal acetylenes with aluminum hydrides in donor solvents [95,96] and (c) the reaction of terminal acetylenes with triorganoaluminums, especially with trimethyl- or triphenylaluminum [91,97]. Where applicable, the last method gives an unsolvated product under mild, simple conditions. 

Triphenylaluminum etherate can be prepared from PhMgX (X = Cl, Br) in 50-75 % yield, although this is not a convenient procedure (see 5.3.3.3.4). In contrast to trialkylaluminums, the ether can be removed by heating the adduct in vacuo. Pure Ph3Al is also obtained from the reaction of ether-free PhMgBr with AICI3 in dodecane in 75 % yield after recrystallization from xylene . 

The reaction between triphenylaluminum and olefins requires drastic conditions (> 200°C). The hydrocarbons formed by subsequent hydrolysis are 2-phenyloctane (from oct-l-ene), 1,1,2-triphenylethane and triphenylethylene (from Ph2C=CH2), exo,exo-2,5-diphenylbicyclo[2.2.1]heptane and exo-5-phenylbicyclo[2.2.1]hept-2-ene (from bicyclo-[2.2.1]hepta-2,5-diene) . 

Tribenzyl- and triphenylaluminum give the cis-addition products with PhC=CPh. With other phenylacetylenes, PhC=CR (R = Me , Bu-t ) and PhjAl regioselective cis addition takes place ... 

Triethyl- and triisobutylaluminum as well as triethyl-, triisobutyl- and triphenylaluminum-etherates undergo addition to cyclic and acyclic nitroalkenes in hexane at 0° or 60 °C, respectively to give the adducts 9 in good yield. In the case of 1-nitrocyclohexene and 1-nitrocyclopcn-tene the clv-isomers of 9 are favored over the trans-isomers128 with the diastereoselectivity increasing with an increase in the steric demand of the alkyl group R. 

The enhancement of migratory insertion is effected by a variety of Lewis acids, including triphenylaluminum (207), in addition to the aluminum halides and boron trifluoride discussed above. An alternative to these molecular Lewis acids is an alumina surface. The dehydration of y-Al203 at elevated temperatures exposes both Lewis acid sites, Al3+, and Lewis base sites, O2- [Eq. (43a)]. When Mn(CO)s(CH3) adsorbs on such a surface an... 

An interesting reaction is that of the salt Na[Al(C2H5)4Cl] with benzene in the presence of sodium alkoxide this gives ethane and sodium tetraphenyl-aluminate Na[Al(C6H5)4], from which triphenylaluminum can be obtained by means of dimethylaluminum chloride. This opens the way to obtain phenyl-aluminum compounds from the ethylaluminum compounds that are readily accessible by direct synthesis.261... 

---