SOLUBLE AND SUPPORTED CARBONYLATION CATALYSTS DERIVED FROM RHODIUM-PHOSPHONATE-PHOSPHANE COMPLEXES

Phosphonate-phosphanes form both chelate and open-chain complexes with rhodium, which can easily be converted into each other. This property has been used in the development of new and efficient carbonylation c atalysts. During the catalytic cycle, the phosphane group is assumed t o be coordinated to the transition metal, while the phosphoryl-oxygen of the phosphonate group is supposed to change between a free and a co ordinated state, thus vacating or occupying a coordination site. IR st udies support the hemilabile behaviour of surface Rh-complexes under t he reaction conditions. Activation enthalpies, obtained for hemilabile rhodium catalysts in homogeneous methanol carbonylation, increased si gnificantly with growing distance between phosphonate and phosphane gr oup. Attempts of preparing stable rhodium complex catalysts adsorbed o n silica or alumina for slurry-phase or vapour-phase carbonylations fa iled. Activated carbon has been shown to be a suitable support for hem ilabile rhodium complexes, but normal diffusion of reactants begins to limit the carbonylation rate over the supported catalysts.