Cationic iridium diolefin complexes as alkene hydrogenation catalysts and the isolation of some related hydrido complexes

Crabtree, Robert H.; Felkin, Hugh; Morris, George E.

doi:10.1016/s0022-328x(00)92273-3

Cited by 348 publications

(170 citation statements)

References 22 publications

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“…Crabtree and co-workers 6,8 showed that deactivation is a consequence of the conversion of the metal complex to hydride-bridged dimers and trimers, which are catalytically inactive. It has also been suggested that deactivation may follow the dissociation of a phosphine ligand from the active species, even where the ligand is bound to a polymeric support.…”

Section: Resultsmentioning

confidence: 99%

Catalyst stability as a factor in iridium‐mediated ortho‐deuteration

Herbert

2007

Labelled Comp Radiopharmac

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Crossover experiments show that iridium complexes such as Ir(cod)(Py)(PCy 3 ).PF 6 (1) and Ir(cod)(PPh 3 ) 2 .BF 4 are inactivated after a comparatively short period during deuterium exchange reactions. This effect can be limited to some extent by optimizing the concentration at which exchange is performed, but altering physical parameters and adding labile ligands in an effort to stabilize reactive intermediates does not improve matters. Complexes of bidentate arsines and PN ligands and, in some cases, bidentate phosphines, exhibit better stability. Unexpectedly, following hydrogenolysis, 1 is able to mediate deuterium exchange from deuterium oxide into amides and N-heterocycles at room temperature.

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Section: Resultsmentioning

confidence: 99%

Catalyst stability as a factor in iridium‐mediated ortho‐deuteration

Herbert

2007

Labelled Comp Radiopharmac

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“…Through the simple exchange of the PF 6 À counterion with the even more weakly coordinating anion tetrakis [3,5-bis(trifluoromethyl)phenyl]borate (BAr F ) [C] it was found that the Ir complexes were more robust and allowed catalyst loading as low as 0.02 mol %. [7,28] Ligands Since this first report by Pfaltz there have been many reports of variations to the N,P-ligand utilised in [B] which have been successfully employed in the hydrogenation of olefins ( Table 1, entries [1][2][3][4][5][6][7][8]. [8] Phosphine-oxazoline ligand I, originally employed by Pfaltz in asymmetric hydrogenation, [7] has evolved into many different classes of successful ligands.…”

Section: Ir-catalysed Hydrogenation Of Olefinsmentioning

confidence: 99%

Ir‐Catalysed Asymmetric Hydrogenation: Ligands, Substrates and Mechanism

Källström¹,

Munslow²,

Andersson³

2006

Chemistry A European J

182

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Relatively air and moisture tolerant cationic iridium complexes, with chiral non-racemic N,P-ligands and weakly coordinating counter ions, are efficient catalysts in the asymmetric hydrogenation of olefins. Unfunctionalised olefins are particularly difficult substrates because, in general, a polar group adjacent to the alkene bond is required for high catalytic activity and enantioselectivity. The applicability towards a variety of substrates and choice of ligands reported thus far in the literature, as well as the mechanism, selectivity issues and the importance of the anion are also discussed.

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“…Utilising related chalcone 1h resulted in ad ecrease in selectivity,p otentially due to aw eaker directing-group complexation (Table 3, entry 3). The weakly coordinating acid 1m showedamoderate selectivity,w hereas the related ester 1n showed ar everse in selectivity to favourt he reduction of 4 (entries [4][5]. This reverse in selectivity can be attributed to the lack of coordinaScheme2.Hydrogenation of enone 1a in different reaction media.…”

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confidence: 97%

“…The foremosth omogeneous catalysts in this area, established by Wilkinson and co-workers [3] and Crabtreea nd co-workers, [4] are applied extensively in organic synthesis. Having stated this, Crabtree's catalyst, although ablet of acilitate mild hydrogenation processes, is thermally unstable and prone to deactivation by the formation of inactivec lusters.…”

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confidence: 99%