期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 20, 期 35, 页码 10982-10989出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201403022
关键词
carbonylation; chemoselectivity; density functional calculations; palladium; reaction mechanisms
资金
- Ministerio de Economia y Competividad (MINECO) of Spain (Ramon y Cajal fellowship) [CTQ2011-29054-C02-01, CTQ2011-27033, CTQ2010-14938/BQU, CTQ2011-22872BQU]
- Generalitat de Catalunya [2009SGR116, 2009SGR259, 2009SGR746, 2009SGR462]
- Generalitat de Catalunya (XRQTC)
- Generalitat de Catalunya (ICIQ Foundation)
The mechanism of the experimentally reported phosphine-free palladium-catalysed carbonylation of aryl iodides with amines in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base was investigated at the DFT level. Paths were identified for both di-and monocarbonylation, and the calculated selectivity for three different substrates was in agreement with experiment. In dicarbonylation yielding a-ketoamides, formation of the second carbon-carbon bond occurs through reductive elimination in the Pd acyl amide intermediate after DBU-assisted nucleophilic attack of an amine at a terminal CO ligand. This path yields the major product with iodobenzene and the almost exclusive product with p-methoxyiodobenzene. Two different possible pathways yield the monocarbonylated amide product. In one of them, which affords the minor product for iodobenzene, base-assisted nucleophilic attack of the amine takes place on a Pd-bound acyl ligand. For substrates with electron-withdrawing substituents, such as p-cyanoiodobenzene, aryl migration to the CO ligand is disfavoured, and this allows base-assisted amine attack at a terminal CO ligand early in the catalytic cycle. From the resulting Pd amide aryl complex, the subsequent reductive elimination occurs easily, and monocarbonylation becomes favoured.
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