ORGN 37 |
| Alkynes have been found to play several roles in palladium catalysis. Under ligand free conditions alkynes can act as stabilizers of active monomeric palladium(0). DFT calculations show that alkynes are as good ligands for palladium(0) as phosphines. The obvious drawback of alkynes is that they will react with Pd-C intermediates, yet in reactions involving alkynes they can act as both ligands and substrates. As substrates, alkynes have been found to react differently compared to the alkene analogues e.g. yielding &alpha-addition products from carbopalladation of &alpha,&beta-acetylenic carbonyl compounds rather than the more intuitive &beta-addition analogues. Resulting from DFT-calculations a rationale for the unexpected reactivity is presented. Finally, in reactions with the bulky P(tBu)3 ligand vinyl-palladium intermediates have been found to rearrange yielding linear products from branched vinyl-tosylate and vinyl-phosphate substrates. A mechanism involving beta-hydride elimination at a vinyl-palladium intermediate to yield an acetylene-palladium-hydride intermediate is proposed.
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
8:00 AM-11:40 AM, Sunday, 10 September 2006 Moscone Center -- Room 133, Oral
Division of Organic Chemistry |
