Bifunctional Lewis acids for the activation of organic carbonyls /
The double activation of ketones and aldehydes by bidentate Lewis acids is attracting considerable interest. It has often been proposed that the unusual activity of bifunctional Lewis acid catalysts in reactions involving organic carbonyls results from their ability to chelate the carbonyl oxygen a...
| Main Author: | |
|---|---|
| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
2002.
|
| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=765073251&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The double activation of ketones and aldehydes by bidentate Lewis acids is attracting considerable interest. It has often been proposed that the unusual activity of bifunctional Lewis acid catalysts in reactions involving organic carbonyls results from their ability to chelate the carbonyl oxygen atom of the substrate, thus providing a double electrophilic activation. However, structural characterization of such chelate complexes remains extremely scarce. In an effort to provide a more complete understanding of the coordination chemistry of polydentate Lewis acids toward carbonyl substrates, the complexation of aldehydes to 1,2-bis(chloromercurio)tetrafluorobenzene (3) and 1,2-bis(cyanomercurio)tetrafluorobenzene (23) has been studied. While 3 does not complex acetaldehyde, compound 23 forms an adduct containing a terminally ligated acetaldehyde ligand. Both complexes form terminal adducts with aromatic aldehydes such as benzaldehyde. In addition, a series of adducts formed by the interaction of trimeric perfluoro-ortho-phenylene mercury, 2, with various aldehydes and ketones have been prepared and characterized. Interestingly, structural characterization of these adducts indicates that the oxygen atom of the carbonyl functionality is triply coordinated to the mercury atoms of 2. In these complexes the Hg-O bonds range from 2.813(6) and 3.056(14) [A] and are within the sum of the van der Waals radii of oxygen and mercury. In all cases, the carbonyl stretching vibration of the carbonyl substrate is shifted to lower wave number which suggests a weakening of the C=O bond. Inspection of the solid state structures of these adducts indicates that various supramolecular forces govern aggregation of the molecular components. In addition to intermolecular arene-perfluoroarene, Hg···Cl, Hg···N, and Hg···F interactions, short metal-metal distances have been detected. Particularly, the structure of [2·[]₃-acetone] reveals the existence of cofacial dimers in which the monomeric units are assembled via short mercurophilic interactions of 3.512 [A]. Efforts to use 23 as a Lewis acid catalyst in the cyanosilylation of benzaldehyde have also been carried out. While pure 23 does not appear to be a very potent catalyst, its combination with TMSCl leads to the formation of a highly active catalytic species. Kinetic studies suggest that 23 behaves as a halophilic bidentate Lewis acid that efficiently induces the formation of a catalytically active silicon species. |
|---|---|
| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xvi, 214 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 135-145). |