INSIGHT INTO Aluminum

T. Krahl, R. Stosser, E. Kemnitz, G. Scholz, M. Feist, G. Silly, J.-Y. Buzare, Structural insights into aluminum chlorofluoride (ACF), Inorg. Chem., 42,6474-6483 (2003). 

There has been little insight into potential decomposition pathways for the Ni(II) system due to sparse experimental evidence. Polymerization results with catalysts bearing different alkyl and fluorinated substituents have suggested that a C-H activation process analogous to that occuring with the Pd(II) catalysts is unlikely with Ni(TT) [28], Instead, side reactions between Ni and the aluminum coactivator, present as it is in such large excess, have been implicated. The formation of nickel dialkyl species and their subsequent reductive elimination to Ni(0) is one possible deactivation mechanism [68]. 

MacPherson GJ, Huss GR, Davis AM (2003) Extinct Be in type A calcium-aluminum-rich inclusions from CV chondrites. Geochim Cosmochim Acta 67 3615-3179 Matthews GJ, Cowan JJ (1990) New insights into the astrophysical r-process. Nature 345 491-494 McCulloch MT, Wasserburg GJ (1978a) Barium and neodymium isotopic anomalies in the Allende meteorite. Astrophys J 220 L15-L19... 

The object of this review is threefold (1) to discuss the various characterization techniques which have been applied to this catalyst system, (2) to relate what each technique reveals about the nature of the catalyst, and (3) to present an overall picture of the state of the catalyst as it now appears. We will not discuss the vast literature on catalyst activity testing, kinetics, or mechanisms here. These are subjects for review themselves. However, we will mention some selective catalyst activity tests which were designed to give some fundamental insight into the catalyst state or active sites present. Also, we will not discuss in detail the considerable work reported on pure compounds (unsupported) of molybdenum, cobalt, and/or aluminum but we will have occasion to compare some of their properties to our catalyst systems to assess to what degree they may be present in the catalyst. 

The siloxides of aluminum can be prepared in the same maimer as the alkoxides and exhibit similar stractural features. Interest in these compounds arose from a desire for sol-gel or polymeric precursors for aluminosilicates. Unfortunately, these compounds extensively hydrolyze, losing most of the silicon as the silanol. However, the investigation of the hydrolysis of (Et3SiO)3Al has generated considerable insight into the stracture and composition of aUcoxy- and siloxy-substitutedalumoxanepolymers, (ROAIO) These macromolecules are now believed to have a structure related to that of boehmite. 

In situ diffraction studies during the release of hydrogen allowed a comprehensive insight into the phase transformation processes taking place during the reversible storage ofhydrogen [113,114]. The decomposition mechanism for sodium aluminum... 

Independently generated low valent zirconocene and titanocene were demonstrated to be competent reagents for defluorination in the absence of terminal reductant. The critical role played by the metallocenes is best illustrated by noting that, in the absence of metallocene, Mg/HgCl2 causes exothermic reduction of perfluorodecalin to carbon. The milder aluminum system only functions in the presence of metallocene. Additional insight into the nature of this multistep process was obtained by showing that plausible flurocarbon intermediates react to afford perfluorodecalin [79]. 

Insight into another mode of formation of these by-products is furnished by the observation that l-chloro-3,3-dimethylpentane and 1-chloro-3,3-dimethylbutane are by-products of the condensation of ethylene with <-butyl chloride and <-amyl chloride, respectively, in the presence of aluminum chloride (Schmerling, 16). Partial conversion of either <-alkyl chloride into the other presumably occurs under the reaction conditions. It is apparent, then, that the alkyl chloride formed as indicated in step 3 of the three step chain mechanism may be converted into a chloride of higher or lower molecular weight before undergoing the condensation of... 

A good insight into the anodic oxide formation is gained from potentiostatic pulse measurements. Figure 19 shows current transients i t) of anodic oxide formation on aluminum at pH = 6.0. Various potential steps from 0 V (hess) were chosen to an oxide formation potential between 3.3 and 5.9 V [77]. This corresponds to an increase in field strength from 6.6 to 10.1 MVcm . The initial film thickness of 7.4 nm is given by a prepolarization to 3V (hess). Each experiment must be performed on a different sample with respect to the irreversible... 

In the growing plastics industry, there is often need to identify polymer formulations. Whether the analysis is done to reproduce the material, identify another supplier, or provide insight into the cause of failure, the filler is an important aspect. Fillers are used for several reasons to extend the amount of polymer for overall eost reduction, to add structural stability or impart specific physical characteristics to the polymer sueh as chemical, temperature, or flame resistance, or to add eolor to a polymer. Several commonly occurring fillers include silicates, aluminum trihydrate, ealcium carbonate, fiberglass, and tale. These fillers have eharacteristic FTIR bands whieh can be easily identified within a speetrum of the polymer. The amount of filler present in the formulation can be of great importanee to the performanee of the polymer. 

Kinetic studies on the dissociation of AlfCHsls from [Cp2M(/r-CH3)2Al(CH3)2] [B(C5H5)4] (M = Ti, Zr, Hf) have been conducted in an effort to provide insight into the mechanism of transfer of alkyl groups from M to Al. Transfer is expected to occur when Zr, for example, is used to catalyze chain growth in aluminum alkyls and when Zr is used to catalyze carboalumination of olefins. The catalytically active species is thought to be a coordinatively unsaturated cationic species Cp2Zr" -CH3, which can be trapped by aluminum alkyls to form the adduct, shown ... 

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