Aluminum complexes crown ethers

Rhinebarger et al. [35] and Eyring et al. [36,37] have used lithium-7 nuclear magnetic resonance (NMR) chemical shift data to determine the stability constants for crown-ether complexes of Li+ in two IL systems consisting of 55/45 mole% N-butylpyridinium chloride-aluminum chloride and l-ethyl-3-methyl-imidazolium chloride-aluminum chloride. The stability constants for... 

While high polymers of /3-lactones can also be formed by cationic polymerization, most of the commercial production seems to be by the anionic route. Carboxylate salts such as sodium acetate or benzoate are commonly the initiators, but other nucleophiles, such as triethylamine, betaine, potassium f-butoxide, aluminum and zinc alkoxides, various metal oxides and tris(dimethylamino)benzylphosphonium chloride (the anion of which is the initiator), are of value. Addition of crown ethers to complex the counter cation increases the rate of reaction. When the reaction is carried out in inert but somewhat polar organic solvents, such as THF or ethyk acetate, or without solvent, chain propagation is very fast and proceeds without transfer reactions. 

X-Ray studies of crown ether complexes of Al reveal some variation in Al—O coordination with ring size. In particular, 15-crown-5 forms (Me3Al)4-crown with Al—O = 200.5 pm, whilst dibenzo-18-crown-6 gives (Me3Al)2-crown with Al—O = 196.7 pm.428 Other facets of crown ether coordination of aluminum are considered in Section 25.1.5.6. 

Primary alkyl amines. a-Alkoxy azides are reduced to primary amines by lithium aluminum hydride in ether. A side reaction noted occasionally, reduction to an ether, can be suppressed by addition of TMEDA. Sodium bis(2-methoxy-ethoxy)aluminum hydride cannot replace lithium aluminum hydride in this reductive amination. The a-alkoxy azides are available by reaction of aldehydes with azidotrimethylsilane, by addition of hydrazoic acid to an enol ether, or by reaction of ketals with the l8-crown-6 complex of sodium azide. 

By the reactions discussed in this manuscript, it is possible to build frameworks which contain aluminum in the presence of quite large numbers of oxygen atoms. For the larger crown ethers this method may allow the placement of more than one AlCl2 ion onto the ring. Cations of some size are envisioned. When these are coupled with aluminoxane anions such as [Aly05Me 5] [10], complexes which have a certain resemblance to zeolites can be foreseen. It remains in later contributions to show that these new compounds can be constructed with shape and size selectivity. 

Though their applications as polymerization catalysts fall outside the remit of the present chapter, a general discussion of the advent of cationic aluminum complexes supported by various ligands is warranted [46]. Over the last two decades cationic aluminum complexes have been very intensively investigated and promise enhanced substrate coordination and activation by virtue of their increased electrophilicity. Early systematic works focused on the use of crown ethers and the synthesis of complexes [Cl2Al(benzo-15-crown-5)][Me2AlCl2] and... 

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