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