Understanding Rh-catalysed Hydroformylation with Phosphite Ligands through Catalyst Speciation Analysis by Operando FlowNMR Spectroscopy

Phosphites are industrially important ligands for the Rh-catalysed hydroformylation of olefins because they produce more active catalysts than phosphines, which is mainly due to their strong pi-acceptor properties facilitating CO dissociation from the metal centre. Herein, the effect of three prominent phosphite ligands (triphenylphosphite, Alkanox and BiPhePhos) on catalyst speciation during turnover is investigated using multi-nuclear operando FlowNMR spectroscopy. The quantitative catalyst distribution maps derived explain activity trends across a range of catalytic reaction conditions that show how phosphites produce more active catalysts, including reduced formation of inactive Rh-0 dimers in the absence of substrate during pre-activation and at the end of the reaction. Additionally, [(alkanox)Rh(acac)] complexes have been found to be of high stability which can be exploited for post-catalytic Rh recovery by simple addition of 2,4-pentanediones.