Operando Spectroscopy and Kinetic Modelling Reveal Dynamic Catalyst Species During Auto‐Oxidation of a Palladium Phosphine System

Ligand oxidation is a reoccurring catalyst deactivation mechanism in catalytic systems containing phosphine ligands. Here we report the use of operando FTIR spectroscopy for the investigation of the aerobic oxidation of the common Pd‐triphenylphosphine catalytic system using [Pd(OAc) 2 ] and [Pd(PPh 3 ) 4 ] as precursors. Kinetics reveal a faster triphenylphosphine consumption than triphenylphosphine oxide formation for low ratios of triphenylphosphine:Pd. With the use of o perando FTIR in combination with hard modeling factor analysis we were able to identify four main catalytic species. A fast transition from a monomeric to a dimeric species was observable starting at triphenylphosphine:Pd of 2.5. Hard‐modelling of the FTIR data exposed two catalytic species: the η 1 and η 2 palladium oxo‐species. It was observed that, the oxidation state of palladium in the precursor used (Pd 0 vs Pd II ) also influenced how protic solvents such as palladium acid affected the oxidation reactions. Kinetic modeling of the Pd 0 experiment further showed that the formed η 1 oxo‐species could be part of the catalytic cycle, while η 2 complex was most likely a resting state.