English   español  
Please use this identifier to cite or link to this item: http://hdl.handle.net/10261/57986
Share/Impact:
Statistics
logo share SHARE logo core CORE   Add this article to your Mendeley library MendeleyBASE

Visualizar otros formatos: MARC | Dublin Core | RDF | ORE | MODS | METS | DIDL
Exportar a otros formatos:

Title

Iridium(I) complexes with hemilabile N-heterocyclic carbenes: Efficient and versatile transfer hydrogenation catalysts

AuthorsJiménez, M. Victoria ; Fernández-Tornos, Javier ; Pérez-Torrente, Jesús J. ; Modrego, Francisco J. ; Winterle, Sonja; Cunchillos, Carmen ; Lahoz, Fernando J. ; Oro, Luis A.
Issue DateSep-2011
PublisherAmerican Chemical Society
CitationOrganometallics 30(20): 5493-5508 (2011)
AbstractA series of neutral and cationic rhodium and iridium(I) complexes based on hemilabile O-donor- and N-donor-functionalized NHC ligands having methoxy, dimethylamino, and pyridine as donor functions have been synthesized. The hemilabile fragment is coordinated to the iridium center in the cationic complexes [Ir(cod)(MeImR)]+ (R = pyridin-2-ylmethyl, 3-dimethylaminopropyl) but remains uncoordinated in the complexes [MBr(cod)(MeImR)], [M(NCCH3)(cod)(MeImR)]+ (M = Rh, Ir; R = 2-methoxyethyl and 2-methoxybenzyl) and [IrX(cod)(MeImR)] (X = Br, R = pyridin-2-ylmethyl; X = Cl, R = 2-dimethylaminoethyl, 3-dimethylaminopropyl). The structure of [IrBr(cod)(MeIm(2-methoxybenzyl))] has been determined by X-ray diffraction. The iridium complexes are efficient precatalysts for the transfer hydrogenation of cyclohexanone in 2-propanol/KOH. A comparative study has shown that cationic complexes are more efficient than the neutral and also that complexes having O-functionalized NHC ligands provide much more active systems than the corresponding N-functionalized ligands with TOFs up to 4600 h–1. The complexes [Ir(NCCH3)(cod)(MeImR)]+ (R = 2-methoxyethyl and 2-methoxybenzyl) have been successfully applied to the reduction of several unsaturated substrates as ketones, aldehydes, α,β-unsaturated ketones, and imines. The investigation of the reaction mechanism by NMR and MS has allowed the identification of relevant alkoxo intermediates [Ir(OR)(cod)(MeImR)] and the unsaturated hydride species [IrH(cod)(MeImR)]. The β-H elimination in the alkoxo complex [Ir(OiPr)(cod)(MeIm(2-methoxybenzyl))] leading to hydrido species has been studied by DFT calculations. An interaction between the β-H on the alkoxo ligand and the oxygen atom of the methoxy fragment of the NHC ligand, which results in a net destabilization of the alkoxo intermediate by a free energy of +1.0 kcal/mol, has been identified. This destabilization facilitates the β-H elimination step in the catalytic process and could explain the positive effect of the methoxy group of the functionalized NHC ligands on the catalytic activity.
Description16 páginas, 5 figuras, 3 tablas, 3 esquemas.
Publisher version (URL)http://dx.doi.org/10.1021/om200747k
URIhttp://hdl.handle.net/10261/57986
DOI10.1021/om200747k
ISSN0276-7333
E-ISSN1520-6041
Appears in Collections:(ISQCH) Artículos
Files in This Item:
File Description SizeFormat 
Ir(I)ComplexesHemilabil.pdf630,8 kBAdobe PDFThumbnail
View/Open
Show full item record
Review this work
 

Related articles:


WARNING: Items in Digital.CSIC are protected by copyright, with all rights reserved, unless otherwise indicated.