Supported mixed bidentate rhodium and iridium complexes derived from phosphonate-phosphanes were studied in the methanol carbonylation and in the hydroformylations of ethylene and propylene. Heterobidentate complexes of rhodium showed higher activities than rhodium bisphosphane complexes in homogeneous and vapour-phase methanol carbonylation. The hemilabile behaviour of the mixed bidentate complexes may explain these findings. In ethylene hydroformylation, supported phosphonate-phosphane Rh-complexes did not show higher activities than supported rhodium-bisphosphane complexes. However, phosphonate-phosphane ligands suppressed the undesired ethane formation in this reaction. Excellent rhodium catalysts for vapour-phase carbonylations were obtained, when Rh phosphane complexes were anchored in lamellar zirconium phosphonate structures with mixed phosphonate anions. These catalysts were several times more active than rhodium supported on silica or on activated carbon, showed a superior stability, and produced butyraldehydes with up to 98% chemoselectivity in the vapour-phase hydroformylation of propylene.