Aluminum coordination

Selenoaldehydes 104, like thioaldehydes, have also been generated in situ from acetals and then directly trapped with dienes, thus offering a useful one-pot procedure for preparing cyclic seleno-compounds [103,104], The construction of a carbon-selenium double bond was achieved by reacting acetal derivatives with dimethylaluminum selenide (Equation 2.30). Cycloadditions of seleno aldehydes occur even at 0 °C. In these reactions, however, the carbon-selenium bond formed by the nucleophilic attack of the electronegative selenium atom in 105 to the aluminum-coordinated acetal carbon, may require a high reaction temperature [103], The cycloaddition with cyclopentadiene preferentially gave the kinetically favorable endo isomer. 

FIGURE 5 Stepwise synthesis of a triblock copolymer (PCL-PLA-PCL) of PCL and polylactic acid using aluminum coordination catalysts to minimize randomization of the block structure by transesterification. (From Ref. 43.)... 

We believe the initial site of attack is on a terminal CO which should be more susceptible than the more electron rich bridging CO s.— The formyl complex will not be "free" but will almost certainly have aluminum coordinated to the oxygen. Further reduction to a methyl could occur as was observed in NaBHi, reduction of CpRe(C0)2N0. We would concur with the statement that the intermediates will all have coordination of the aluminum to the oxygen during the reduction. We have demonstrated in a separate experiment that methane is formed when CH3FeCp(C0)2 is reacted with LAH. 

Instead of using high-temperature melting to make the precursor alloys, an alternative wet chemistry technique has been proposed where nickel(O) and aluminum coordination compounds are blended together and treated to give nanocrystalline NiAlx alloys with 1 < x < 3 [48], The alloys are leached in the same way as standard skeletal catalysts. Catalysts with higher activity than commercially available Raney nickel have been prepared by this technique, with the activity attributed to the finer structure and homogeneity of the alloys [48,49],... 

To investigate the hydration and dehydration processes of H-SAPO-34 and H-SAPO-37, H and Al MAS NMR spectroscopy was applied under CF conditions with the equipment shown in Fig. 12 (217). The chemical behavior and the change of the silicoaluminophosphate framework were monitored as nitrogen loaded with water or dry nitrogen was injected into the MAS NMR rotor filled with the silicoaluminophosphates. By this approach, the primary adsorption sites of water in silicoaluminophosphates and the variation of the aluminum coordination were observed. Furthermore, the formation of framework defects and the conditions of water desorption were characterized. 

It is necessary to pay attention to the fact that, during recent years, the bioinorganic properties of aluminum coordination compounds have become the objects of detailed study their general aspect [354], metabolism and toxicology [355,356], complex formation with nucleozides of di- and triphosphates and nucleo-zide-bound proteins [357], and x-ray analysis of biologically important complexes... 

NMR peaks in the range of -187 to -194 ppm (19F-NMR) and 49 to 52 ppm (27Al-NMR) were observed for the TFA salts prepared via anhydrous routes. Thus, they correspond to tetrahedral aluminum coordinated by four fluorine atoms. This is demonstrated, for example, in the coupling for [PSH] [TFA] in CD3CN, which was observed as a sextet from 19F-27Al in the 19F-NMR, and a quintet from 27Al-19F in the solid state 27Al-NMR. 

I). Actually, the highest regioselectivity is observed with organoalane derivatives, possibly because aluminum coordinates with both oxygens in the substrate. This reaction was useful in syntheses of prostaglandin analogs. 

Omegna, A., Prins, R. and van Bokhoven, J.A. (2005) Effect of temperature on aluminum coordination in zeolites H-Y, H-USY and amorphous silica-alumina an in-situ A1 K edge XANES study J. Phys. Chem. B, 109, 9280-9283. 

Gilbert et al. (1996) have shown that the aluminum ion prefers fluoride over chloride to such an extent that when Na3Alp6 is dissolved in NaCl, no chloride enters the aluminum coordination sphere and no evidence of mixed aluminum fluoro-chloro complexes is found. 

Bodor, A., Bdnyai, L, and Tdth, 1. (2002). H- and C-NMR as tools to study aluminum coordination chemistry aqueous Al(ni)-citrate complexes. Coord. Chem. Rev. 228. 175-186. 

BEt3 was clearly most effective when the catalyst P/Al ratio was low and when the catalyst was activated at low temperatures. The cocatalyst seems to counteract the effect of poor dehydroxylation and low P/A1 ratios. Because higher activation temperatures remove surface OH groups (potential ligands on the chromium), and because the average aluminum coordination shifts from octahedral to tetrahedral as P/Al increases, one interpretation of this trend is that cocatalyst may remove ligands from coordinating to the Cr site, as does the activation temperature or the P/Al ratio. 

Neighboring group effects can compete with steric effects, as illustrated by treatment of oxetane 142 with diethylaluminum-At-methylaniline. This elimination reaction gave a 99% yield of (E)-alkene 143 in a synthesis of humulene. The aluminum coordinated to the oxetane oxygen on the less hindered p face in 144 and 145, the two key rotamers. Rotamer 144 is lower in energy due to the severe nonbonded interaction... 

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