Impact of dioxygen and carboxylic acids on the transformation of rhodium(I) to rhodium(III) complexes

Abstract

The reaction of the hydroformylation catalyst precursor [Rh(acac)(CO)(PPh₃)](acac = acetylacetonate) with dioxygen and salicylic acid led to the formation of the rhodium(III) complexes [Rh(acac)(HOC₆H₄CO₂)₂(PPh₃)(H₂O)] and [Rh(acac)₂(HOC₆H₄CO₂)(PPh₃)]. The structures of the latter complexes were characterized spectroscopically (¹H and ³¹P NMR) as well as by X-ray crystallography. Dioxygen activation by Rh¹ proceeds through peroxo [Rh(O₂)(HOC₆H₄CO₂)(CO)(PPh₃)] and hydrogen dioxide [Rh(O₂H)(acac)(HOC₆H₄CO₂)(CO)(PPh₃)] complexes identified by IR UV/VIS and ³¹P NMR methods. Oxidation of CO to CO₂ occurs in the inner co-ordination sphere of rhodium.