Aluminum complexes carbonates

A living radical polymerization mechanism was proposed for the polymerization of MMA23 -240 and VAc241 initiated by certain aluminum complexes in the presence of nilroxides. It was originally thought that a carbon-aluminum bond was formed in a reversible termination step. However, a more recent study found the results difficult to reproduce and the mechanism to be complex.242... 

A rather different allene cyclization that takes place in tandem with an alkylative process has been described by Trost and Urabe [66] (Eq. 13.52). Exposure of ketoal-lene 169 to divinylmethylaluminum 170 in dichloromethane solution leads to 171 in 60% yield. The mechanism of this alkylative cyclization involves complexation of the Lewis acidic aluminum to the carbonyl oxygen atom, followed by ring closure, leading to zwitterion 172. Intramolecular transfer of a vinyl group from aluminum to carbon completes the process. 

Its molecular structure (Figure 37) consists of a centrosymmetric dimer with a bridging H2Al(OR)( U-OR)2Al(OR)H2 entity. The Ta atoms are approximately square pyramidal, with the four phosphorus atoms forming the basal plane (Ta lies 0.64 A out of it). The relatively short Ta—A1 distances are comparable to those found in other transition metal aluminum complexes (Ta—Al 2.79-3.13 A). The hydrogen atoms have not been located, but were evidenced by chemical and spectroscopic techniques (IR 1605, 1540 cm 1 HNMR 16.30p.p.m.). The Ta—(ju-H2)A1 unit is relatively stable, and (54) is inert to carbon monoxide or trimethylamine. It is a poor catalyst in the isomerization of 1-pentene. Formation of complexes analogous to (54) may explain the low yields often obtained from alkoxoaluminohy-drides and metal halides. 

Reduction then proceeds by successive transfers of hydride ion, H e, from aluminum to carbon. The first such transfer reduces the acid salt to the oxidation level of the aldehyde reduction does not stop at this point, however, but continues rapidly to the alcohol. Insufficient information is available to permit very specific structures to be written for the intermediates in the lithium aluminum hydride reduction of carboxylic acids. However, the product is a complex aluminum alkoxide, from which the alcohol is freed by hydrolysis ... 

Ti—13Cp 40.1 ppm), and only weak signals of 13C-labeled alkyl groups at the aluminium were observed (see Fig. 6). These results indicate that an insertion of ethylene takes place into a titanium-carbon bond of a titanium-aluminum complex and no alkyl exchange between the bonds of titanium-alkyl and aluminum-alkyl occurs. 

The mechanism for both of these reactions is very similar to the mechanism for the reduction of acyl chlorides by LATB—H. The first step is an acid-base reaction between an unshared electron pair on oxygen or nitrogen with the aluminum atom of the DIBAL—H. The second step is the transfer of a hydride ion from the DIBAL—H to the carbon atom of the carbonyl or nitrile group. The last step is the hydrolysis of the aluminum complex to form the aldehyde. 

Concomitant with continued olefin insertion into the metal-carbon bond of the titanium-aluminum complex, alkyl exchange and hydrogen-transfer reactions are observed. Whereas the normal reduction mechanism for transition-metal-organic complexes is initiated by release of olefins with formation of hydride followed by hydride transfer (184, 185) to an alkyl group, in the case of some titanium and zirconium compounds a reverse reaction takes place. By the release of ethane, a dimetalloalkane is formed. In a second step, ethylene from the dimetalloalkane is evolved, and two reduced metal atoms remain (119). 

Sinn and Patat (59) drew attention to the electron-deficient character of those main group alkyls that afford complexes with the titanium compound. Fink et al. (51) showed by 13C NMR spectroscopy with 13C-enriched ethylene at low temperatures (when no alkyl exchange was observed) that, in the more highly halogenated systems, insertion of the ethylene takes place into a titanium-carbon bond of a titanium-aluminum complex. 

Aluminum Organometallic Chemistry Carbene Complexes Carbon-Carbon Carbon-Heteroatom Activation ... 

Existence of carboxylate-Al(ni)-OH dimers has been inferred from a large number of very careful potentiometric studies of aluminum complexation by organic acids (e g., oxalic acid—Sjoberg and Ohman 1985 lactic acid—Marklund and Ohman 1990 phthalic acid— Hedlund et al. 1987a carbonic acid—Hedlund et al. 1987b). None of these postulated dimeric structures have been yet confirmed by X-ray structural study of... 

Alexjto) Sodium Sodium polyhydroxyaluminum monocarbonate hoxuol complex aluminum sodium carbonate hexitol complex ActaL Probable structure and properties Gwilt et al, J. Pharm, Pharmacol 10 770 (1958). 

Aluminum(III) hydroxyfluorides minerals, 846 Alzheimer s disease aluminum removal, 770 Amberlite LA 2 solvent extraction palladium and platinum, 809 Americium breeder reactor fuels Purex process, 955 reprocessing, 954 Purex process, 946,950 sequestering agents, 962 Americium(III) complexes carbonates... 

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