Aluminum compounds interactions

The adhesion of metal and ink to polymers, and the adhesion of paint and other coatings to metal, are of vital importance in several technologies. Aluminum-to-alu-minum adhesion is employed in the aircraft industry. The strength and durability of an adhesive bond are completely dependent on the manner in which the adhesive compound interacts with the surfaces to which it is supposed to adhere this, in turn, often involves pretreatment of the surfaces to render them more reactive. The nature and extent of this reactivity are functions of the chemical states of the adhering surfaces, states that can be monitored by XPS. 

Stereoelectronic factors are also important in determining the stmcture and reactivity of complexes. Complexes of catbonyl groups with trivalent boron and aluminum compounds tend to adopt a geometry consistent with directional interaction with one of the oxygen lone pairs. Thus the C—O—M bond angle tends to be in the trigonal (120-140°) range, and the boron or aluminum is usually close to die carbonyl plane. ... 

If substantial stabilization results from metal-metal interactions, then the large A1—Al separation (approximately 3.0 A) observed in the phenylethynyl-bridged aluminum compound is of major importance since it would lead to greatly reduced metal-metal interaction. This would require that the estimate of tt - metal interaction is far too low and would, in fact, have to be of the order of 15 kcal/mole to account for the stability of the dimeric species. 

XXXVII we also see a bridging group with Al—C distances very close to that observed in other bridged aluminum compounds. The distance between the metal centers in this compound is similar to that observed in the simpler aluminum derivatives but greater than the sum of the covalent radii of the two metals (2.54 A), which may be an indication that Ti—Al interactions do not increase the stability of the bridged system. Structures on Cp2MMe2AlMe2 (M = Y, Er, and Yb) have been recently completed and clearly show stable electron-deficient bonds between the aluminum and the transition metal moiety (XXXVIII) (12). 

Weberg and Berstad 1986 Yokel and McNamara 1988). The effect has been shown with a variety of aluminum compounds and several forms of citrate in both experimental and clinical studies. The combination of citrate and aluminum has been responsible for a number of deaths in uremic patients, and the clinical implications of the interaction has led some investigators to advise against concomitant exposure to aluminum and citrate in any form (e.g., antacids and orange juice), especially to patients with impaired renal function. As discussed in Sections 2.3.1.2 and 2.4.1, citrate complexes with aluminum to form a species that is particularly bioavailable in the near-neutral pH conditions of the intestines. 

Several animal studies have examined potential age-related differences in the distribution, neurotoxicity, skeletal toxicity, and interactions of aluminum. However, conflicting results have been found and the database is not adequate to assess whether these differences are due to the animal species tested, the aluminum compound used, or the route of exposure. Additionally, there are no studies on the influence of immature renal function on aluminum retention in the body and no studies on the long-term effects of aluminum exposure on skeletal maturation or neurotoxicity. Multiple species studies examining a wide range of effects in immature, mature, and older animals would be useful in assessing the children s susceptibility to the toxicity of aluminum. 

Two types of publications are presented herein. The first set outlines the toxic effects of aluminum compounds on various living systems. The second set, comprised of two papers, deals with the formation and activity of aluminum fluoride compounds. The Volume begins with a chapter by Berend Acute Aluminum Intoxication that outlines the myriad toxic effects aluminum can have once it has by-passed an organisms protective barriers. This occurs in humans, for example, when aluminum salts are used in medicine (a practice that has now been eradicated). The in-depth coverage of this topic provides an excellent background for understanding the chemical interactions associated with aluminum that are described subsequently in Chapters 2-4. 

Substituents in the alkyl chain of alkyl aluminum compounds, such as halogens, alkoxy, alkylmercapto, or dialkylamino groups, have varying effects on the stability of the aluminum alkyls to extents which depend on the position of the group in relation to the aluminum. Interaction between the substituents and aluminum leads to activation of both the A1—C and the C-substituent bonds. If, in the case of dialkyl halomethylalanes, the substituent (Cl, Br, or I) and the aluminum are linked to the same carbon atom, the compound is especially reactive. These compounds, since their etherates are stable, may be prepared readily in ethereal solution from dialkyl aluminum halides and diazomethane 97, 98) ... 

Because of its high localized dipole moment, sulfolane is a very good solvent for inorganic salts, and its effect on the acylation activity of Y(9) is ascribed to the formation of a homogeneous catalyst system consisting of dissolved aluminum compound that interacts with BC. Blank experiments and Al NMR analysis of the solution confirm the activity after filtration of the catalyst. These results are not so negative and confirm that a catalytic amount of aluminum species are transferred into solution in sulfolane and catalyzes the quantitative conversion of BC. 

There is ample evidence, however, that certain alkynyl- and alkenyl-aluminum compounds do exhibit inter- or intramolecular interactions between their w-bonds and aluminum centers (62, 87). 

Carboxyl mononiers have been protected in several ways for Z-N polymerization. In one method, the carboxyl functionality is first converted to an ester group and subsequently precon lexed with an aluminum compound to further mute its reactivity with Z-N catalysts . The precomplexed ester monomer (29) is stable to Z-N conditions and is removed during work-up. Of course, the ester groups can be further hydrolyzed to carboxylic acids or salts, which can associate via hydrogen bonding or ionic interactions. 

The general consensus on the mechanistic details of transition metal-catalyzed polyethylene formation is that the active site comprises a metal with an alkyl group as active chain end and a free coordination site, with the metal incorporated in a ligand or in a salt crystal [32]. Ethylene is inserted in a syn fashion into the metal-carbon bond. Iron bis(iminoaryl)pyridyl dichloride (BI P FeCl2, where R denotes the ortho substituents on the aryl entity Fig. 1) in combination with MAO or (tri)alkyl aluminum compounds (AIR3) yields active ethylene polymerization systems [23]. Both the free coordination site and the alkyl group of the iron center thus originate from the interaction with the aluminum compounds. 

Ketones a-Olefins bearing keto functionalities show also only weak interactions with aluminum compounds resulting in insuffident proteaion for the successful polymerization by transition metal catalysts. Additionally, undesired side reactions, for example, the keto-enol tautomerization of 2,2-dimethyl-11-dodecen-3-one in combination with MAO were reported. ... 

This chapter seeks to update the recent literature concerning organometallic compounds of Al(III) [1-19]. Heterobimetallic systems are essentially excluded from the present contribution, even where there is no inter-metal interaction and the aluminum is in the +111 oxidation state. Some of these aspects are discussed in detail in [286]. Whilst this eliminates the extensive subsection of heterometallic aluminum compounds known as ate complexes, these have been reviewed elsewhere [20]. 

B(C6p5)3, the monomeric compound HC C(Me)NDipp 2Al formed a Lewis adduct that features a short Al—F interaction with one of the o-fluorines of the B(C6F5)3 group (Fig. 5) [90]. The fluorine atom essentially donates electron density to the formally empty p-orbital located on the aluminum center, as supported by theoretical calculations [90,91]. This is the first example of an aluminum compound containing an Al center behaving as a Lewis amphoter. 

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