Isolation of an σ-alkyl iridium hydride complex, formed in the (semi)hydrogenation of an β-enamido ketone.

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.