title: Pd-catalysed mono- and dicarbonylation of aryl iodides: insights into the mechanism and the selectivity.
abstract: 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 α-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.
authors.affiliation: Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, C/Marcel.li Domingo s/n, 43007 Tarragona (Spain), Fax: (+34) 977-559-563; Institute of Chemical Research of Catalonia (ICIQ), Av Països Catalans 16, 43007 Tarragona, Catalonia (Spain), Fax: (+34) 977-920-231.
authors.forename: Victor M
authors.initials: VM
authors.lastname: Fernández-Alvarez
authors.forename: Verónica
authors.initials: V
authors.lastname: de la Fuente
authors.forename: Cyril
authors.initials: C
authors.lastname: Godard
authors.forename: Sergio
authors.initials: S
authors.lastname: Castillón
authors.forename: Carmen
authors.initials: C
authors.lastname: Claver
authors.forename: Feliu
authors.initials: F
authors.lastname: Maseras
authors.forename: Jorge J
authors.initials: JJ
authors.lastname: Carbó
keywords: carbonylation; chemoselectivity; density functional calculations; palladium; reaction mechanisms