Isolation of an σ-Alkyl Iridium Hydride Complex, Formed in the (Semi)hydrogenation of an β-Enamido Ketone

Abstract

σ-Alkyl iridium hydride complexes are generally postulated as intermediates in iridium-catalyzed hydrogenation. Fast reductive elimination results in the formation of the hydrogenation product. With an β-enamido ketone as unsaturated substrate, such an intermediate could be trapped because the semihydrogenated product coordinates trifold to the iridium, generating a stable 18e(-) complex, which does not eliminate.

Enantioconvergent and enantiodivergent catalytic hydrogenation of isomeric olefins

“…The Burgess group proposed a model involving the chelation of the carbonyl group to the Ir metal center and in following studies several pathways involving a chelation were suggested to explain the enantioselective outcome obtained from a,b-unsaturated molecules. [68][69][70] In 2016, Bolm and co-workers investigated the mechanism of the hydrogenation of a,b-unsaturated ketones using an Iridium sulfoximine catalyst by means of DFT studies. Substrate chelation was proposed in this case as well and, in contrast with previous studies, the coordination of the olefin was proposed to be trans to the ligand nitrogen atom.…”

Mechanistic Insights into the Iridium‐Catalyzed Hydrogenations of α,β‐Unsaturated Ketones

“…Kazmaier and Maurer isolated a σ‐alkyl iridium complex, which was suggested to be a possible intermediate in the hydrogenation of β‐enamido ketones with an iridium phosphinite oxazoline catalyst . Probably general for related complexes of this type, the compound showed a keto‐to‐Ir coordination.…”