Operando Infrared Spectroscopic and Quantum-chemical Studies on Iridium-catalyzed Hydroformylation

Hydroformylation of 1-butene using a triphenylphosphine-modified iridium catalyst was investigated by operando infrared spectroscopy. The spectra were interpreted by comparison with quantum-chemically calculated vibrational spectra at the density functional theory level. The processes during activation of the catalyst and hydroformylation were investigated in detail, and the results are discussed. The recently discovered phenomenon of activity enhancement in iridium-catalyzed hydroformylation by a preceding activation step, in which the reaction mixture is treated with synthesis gas containing an excess of carbon monoxide under pressure, could be correlated with the appearance of a complex HIr(PPh₃)(CO)₃. The similarities and differences between iridium- and rhodium-catalyzed hydroformylation are discussed.