Lewis acid catalysts, eg. Fe3+, Ru3+, Zn2+, etc., for certain organic transformations - Thesis Proposal Example

te possesses a series of basic sites, reaction specificity is necessary for that particular interaction between acid and base so that the desired functionality is achieved and not the other. The Lewis acid predetermines the nature of the intermediate cationic specie. It can be an ion pair, a covalent compound with weak C-X bond or an intermediary compound (Suzuki 1557). Lewis acids found their applications in a range of carbon-carbon forming reactions. Usually, Mukaiyama aldol synthesis (Mukaiyama, Banno, and Narasaka 7503), Diels-Alder reactions (Clayden, Greeves, Warren, and Wothers 905) ene reactions and Friedel-Crafts reaction (Clayden, Greeves, Warren, and Wothers 920) are catalysed by commonly employed Lewis acids such as BF3, TiCl4, SnCl4 and AlCl3.

These compounds can activate a series of organic groups and usually exist as dimers, trimmers or oligomers. In most cases, such reactions are highly efficient but with little or no chemo, region or stereoselectivity. It was noted that only small changes in ligands, surrounding the central metal ion can lead to monomeric structures in organic solvents thus increasing their acidity and reactivity. Also, these changes in ligands change the way the newly formed Lewis acids interact with their substrates, thus manifesting new selectivity (Yamamoto and Saito 239).

As an example of the idea presented above, two compounds can be put forward: MAD (bis(2,6-di-tert-butyl-4methylphenoxide) methylaluminum) and ATPH (tris(2,6-diphenylphenoxide) tris(2,6-diphenylphenoxide)). Both compounds were prepared from Me3Al and the corresponding, highly substituted phenol according to the scheme below: Both compounds are highly useful in highly specific chemical transformation. It is possible to lower the activity of the Lewis acids prepared in a way that ATPH was by taking more electron donating organic substrates.

Comparing to conventionally employed Lewis acids, it was established that the steric effect of the presented above