Oxidation and ß-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands

Jiménez, M. V. (Universidad de Zaragoza) ; Fernández-Tornos, J. ; Modrego, F. J. (Universidad de Zaragoza) ; Pérez-Torrente, J. J. (Universidad de Zaragoza) ; Oro, L. A. (Universidad de Zaragoza)

Resumen: The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for C-C bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and ß-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex Ir(NCCH3)(cod)(MeIm(2- methoxybenzyl))]BF4] (cod=1, 5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0) of 1283 h-1, and also in the ß-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new C-C bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.

Idioma: Inglés

DOI: 10.1002/chem.201502910

Año: 2015

Publicado en: Chemistry - A European Journal 21, 49 (2015), 17877-17889
ISSN: 0947-6539

Factor impacto JCR: 5.771 (2015)

Categ. JCR: CHEMISTRY, MULTIDISCIPLINARY rank: 24 / 162 = 0.148 (2015) - Q1 - T1

Factor impacto SCIMAGO: 2.461 - Chemistry (miscellaneous) (Q1)

Financiación: info:eu-repo/grantAgreement/ES/MINECO-FEDER/CTQ2013-42532-P

Tipo y forma: Artículo (PostPrint)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)