From Olefin Coordination to Rh─N Bond Formation and Oxidative Addition: pH Effects in Rhodium α‐Methyl‐β‐Amidoitaconate Complexes

The understanding of the nature of catalyst–substrate complexes is key for the optimization of catalytic transformations such as asymmetric hydrogenation of prochiral olefins. We present a crystallographic and NMR spectroscopic study of coordination of the prochiral olefin α‐methyl‐β‐amidoitaconate to two [Rh(diphosphine)] + fragments under varying pH conditions. While under neutral conditions substrate coordination is observed, yielding the expected Rh(I)–substrate complexes, the coordination under basic conditions results in the deprotonation of the amide group, giving neutral Rh(I) complexes that possess covalent Rh–N linkages. At low pH, oxidative addition of the acid induces 1,2‐insertion of the olefin functional group into the Rh hydride, resulting in the formation of Rh(III) alkyl complexes that are commonly regarded as catalytically inactive species for hydrogenation. The NMR spectroscopic aspects of these rare transformations are investigated using a combination of low‐field flow and high‐field NMR spectroscopy. Finally, the relevance of these observations for asymmetric hydrogenation of α‐methyl‐β‐amidoitaconate is discussed.