Aluminum-transition metal complexes

Acetonitrile also is used as a catalyst and as an ingredient in transition-metal complex catalysts (35,36). There are many uses for it in the photographic industry and for the extraction and refining of copper and by-product ammonium sulfate (37—39). It also is used for dyeing textiles and in coating compositions (40,41). It is an effective stabilizer for chlorinated solvents, particularly in the presence of aluminum, and it has some appflcation in... 

Ziegler-Natta catalysts-—there are many different formulations—are organometallic transition-metal complexes prepared by treatment of an alkyl-aluminum with a titanium compound. Triethylaluminum and titanium tetrachloride form a typical preparation. 

The racemization mechanism of sec-alcohols has been widely studied [16,17]. Metal complexes of the main groups of the periodic table react through a direct transfer of hydrogen (concerted process), such as aluminum complexes in Meerwein-Ponn-dorf-Verley-Oppenauer reaction. However, racemization catalyzed by transition metal complexes occurs via hydrogen transfer processes through metal hydrides or metal dihydrides intermediates (Figure 4.5) [18]. 

In summary, many attempts have been made at achieving enantioselective reduction of ketones. Modified lithium aluminum hydride as well as the ox-azaborolidine approach have proved to be very successful. Asymmetric hydrogenation catalyzed by a chiral ligand-coordinated transition metal complex also gives good results. Figure 6-7 lists some of the most useful chiral compounds relevant to the enantioselective reduction of prochiral ketones, and interested readers may find the corresponding applications in a number of review articles.77,96,97... 

Since the discovery by Ziegler and Natta that transition metal complexes, in the presence of aluminum alkyl compounds, can efficiently catalyze the polymerization of ethylene and propylene, significant efforts have been devoted to the development of new catalytic systems for polymerization of olefins. One of the... 

A limitation of aluminum-containing ionic liquids arises from their moisture sensitivity. Moreover, most transition metal complexes and organic reactants are not unreactive in the presence of the chloroaluminate compounds. These ionic liquids react with water in a highly exothermic manner, with the formation of hydrogen chloride and a white precipitate. 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

The development of mesoporous materials with more or less ordered and different connected pore systems has opened new access to large pore high surface area zeotype molecular sieves. These silicate materials could be attractive catalysts and catalyst supports provided that they are stable and can be modified with catalytic active sites [1]. The incorporation of aluminum into framework sites of the walls is necessary for the establishment of Bronsted acidity [2] which is an essential precondition for a variety of catalytic hydrocarbon reactions [3], Furthermore, ion exchange positions allow anchoring of cationic transition metal complexes and catalyst precursors which are attractive redox catalytic systems for fine chemicals [4]. The subject of this paper is the examination of the influence of calcination procedures, of soft hydrothermal treatment and of the Al content on the stability of the framework aluminum in substituted MCM-41. The impact on the Bronsted acidity is studied. 

Aluminum—tetradentate ligand catalyst system, in epoxide homopolymerization, 11, 601 Aluminum(I) tetrahedra, synthesis, 9, 262 Aluminum(III)-tin exchange, process, 9, 265 Aluminum-transition metal bonds, characteristics, 9, 264 Amavadine, for alkane carboxylations, 10, 234—235 Ambruticin S, via ring-closing diene metathesis, 11, 218 Amide-allenes, cyclizations, 10, 718 Amide ether complexes, with Zr(IV) and Hf(IV), 4, 783 Amide hybrid ligands, in organometallic synthesis, 1, 64 Amides... 

Organoaluminum compounds also have applications in the synthesis of inorganic and organometallic complexes of the transition metals. Since aluminum is more electropositive than most of the transition metals, aluminum alkyls are excellent alkylating agents for transition metal complexes. Alkylation followed by subsequent -hydrogen and reductive elimination (e.g. equation 32) is a convenient means of reducing transition... 

It has been reported that several transition metal complexes catalyze the hetero-Diels-Alder reaction between a variety of aldehydes, in particular benzaldehyde, and Danishefsky s diene (Sch. 52). With the [CpRu(CHIRAPHOS)] complex the ee is modest (25 %) (entry 1) [192]. The chiral complex VO(HFBC)2 performs better in this reaction (entry 2) [193]. In experiments directed towards the synthesis of anthra-cyclones, this complex was used in cycloadditions between anthraquinone aldehydes with silyloxy dienes. One example is shown in Sch. 53 [194]. Compared with the chiral aluminum catalyst developed earlier by Yamamoto and co-workers [195], the vanadium catalyst results in lower enantioselectivity but has advantages such as ease of preparation, high solubility, stability towards air and moisture, and selective binding to an aldehyde carbonyl oxygen in the presence of others Lewis-basic coordination sites on the substrate. 

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