Secondary Phosphane Oxides as Preligands in Rhodium-Catalyzed Hydroformylation

Four aryl-substituted secondary phosphane oxides (SPOs) were tested as preligands in the rhodium catalyzed hydroformylation of cyclohexene and 1-octene. Three of them form active hydroformylation catalysts through their phosphinous acid tau, tomers. n-Regioselectivities of up to 56% were achieved in the reaction with the linear olefin. The catalytic system with the electron-poor SPO showed exceptional behavior. In situ high-pressure IR spectroscopic investigations accompanied by DFT calculations provide an explanation of the observed inhibition of the catalytic reaction. Furthermore, proof is given that non-coordinated SPOs readily react with product aldehydes at room temperature to form alpha-hydroxyphosphinic acids. In contrast Rh-catalyzed hydrophosphination did not take place.